mirror of
https://github.com/FunKey-Project/FunKey-Project.github.io.git
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change directory structure to match index
Signed-off-by: Michel-FK <michel.stempin@funkey-project.com>
This commit is contained in:
Michel-FK
78
docs/developer_guide/hardware_reference/architecture.md
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78
docs/developer_guide/hardware_reference/architecture.md
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@@ -0,0 +1,78 @@
|
||||
|
||||
## Block Diagram
|
||||
|
||||
Eventually, the design constraints listed in the previous section led
|
||||
to the following electronic diagram, featuring 3 main blocks:
|
||||
|
||||
- 1x main PCB (0.8 mm thickness) with components on both sides, the
|
||||
maximum component height above PCB on both sides is 1.5 mm. Current
|
||||
revision for this board is Revision E
|
||||
|
||||
- 1x 1.54” IPS TFT LCD screen with SPI interface and using a
|
||||
custom flex cable, containing a built-in screen controller chip
|
||||
|
||||
- 1x 420 mAh 402540 LiPo battery, containing an active protection
|
||||
circuitry
|
||||
|
||||
{.lightbox}
|
||||
|
||||
## 3D View
|
||||
|
||||
A 3D rendering of the PCBA done in KiCAD produces the images below:
|
||||
|
||||
{.lightbox}
|
||||
|
||||
{.lightbox}
|
||||
|
||||
## BOM
|
||||
|
||||
An interactive BOM is available in the [next section][1].
|
||||
|
||||
## Schematics and Layout
|
||||
|
||||
All the hardware design and production files required to build the
|
||||
[**FunKey S** retro-gaming console][2] electronic PCBA using the
|
||||
[KiCAD ECAD tools][3] are available as Open Hardware in the [FunKey S
|
||||
Hardware repository][4].
|
||||
|
||||
???+ note "Topological vs. logical schematic symbols"
|
||||
|
||||
The **FunKey S** schematics use symbols and placement that are as
|
||||
close as possible to their corresponding physical package and
|
||||
layout, instead of defining symbols that are conveniently arranged
|
||||
by logical properties. Even if this makes schematics more complex
|
||||
at first sight, the benefit of this approach is that the step to
|
||||
go from the schematics to the physical layout becomes much easier,
|
||||
and so is the debugging of the physical board, which is then very
|
||||
close to the schematics too.
|
||||
|
||||
???+ note "Explicit schematic wires"
|
||||
|
||||
Another habit that is used everywhere in the **FunKey S**
|
||||
schematics is that all signals (except power supplies and GND) are
|
||||
routed using explicit wires, rather than counting on invisible
|
||||
connection by net names and relying of the reader to search these
|
||||
names all over the place. This forces related components to be
|
||||
clustered in compact groups to shorten the wires, and put more
|
||||
focus on inter-cluster signals, with a natural inclination to
|
||||
unravel wire nests in the schematics before laying out the actual
|
||||
board.
|
||||
|
||||
???+ note "Power supply nets"
|
||||
|
||||
There are some "PWR_FLAG" symbols added here and there, which is
|
||||
the proper way in KiCAD to declare that a given net has a known
|
||||
supply and thus prevent the ERC (Electrical Rule Check) to throw
|
||||
an error.
|
||||
|
||||
The schematics will be discussed function by function in the following
|
||||
sections.
|
||||
|
||||
[1]: https://htmlpreview.github.io/?https://github.com/FunKey-Project/FunKey-S-Hardware/blob/master/BOM/ibom.html
|
||||
[2]: https://www.funkey-project.com/
|
||||
[3]: https://kicad.org/
|
||||
[4]: https://github.com/FunKey-Project/FunKey-S-Hardware
|
||||
|
||||
--8<--
|
||||
includes/glossary.md
|
||||
--8<--
|
||||
84
docs/developer_guide/hardware_reference/audio.md
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84
docs/developer_guide/hardware_reference/audio.md
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|
||||
Playing audio is absolutely part of the gaming experience!
|
||||
|
||||
So for a retro gaming console like the **FunKey S**, having a decent
|
||||
audio playback is a requirement, despite its lilliputian size.
|
||||
|
||||
We discarded the solution of using a piezo-electric buzzer: these can
|
||||
get a loud sound in a small volume, but only at their resonance
|
||||
frequency, so the sound quality is extremely poor.
|
||||
|
||||
Turning back to the solutions used in modern smartphones as an
|
||||
example, there are 2 paths to consider:
|
||||
|
||||
- playing audio internally by the mean of speaker(s)
|
||||
|
||||
- playing audio externally by using headphones, with or without a cord
|
||||
|
||||
The speakers used in today's smartphones are rather sophisticated and
|
||||
achieve very good performance. However, these are using
|
||||
made-to-measure speakers and cavities, such that they cannot be found
|
||||
and reused as standard parts in a design like ours.
|
||||
|
||||
As for the external audio solution, the **FunKey S** is so small that
|
||||
it is not possible to integrate an audio jack on the PCB to connect
|
||||
headphones! And despite our search, there is no simple and small
|
||||
enough way to integrate Bluetooth to output audio to cordless
|
||||
headphones either.
|
||||
|
||||
{: align=left }
|
||||
|
||||
The best solution we have found consists in using a single tiny [CUI
|
||||
CDM-10008][1] speaker, that is able to output 72 dB spl @ 1m from a
|
||||
0.3W input power, with relatively modest dimensions: 10 mm diameter
|
||||
and only a 2.9 mm thickness, out of which 1.4 mm can be inserted into
|
||||
a PCB hole, thus only having a height above PCB of only 1.5 mm.
|
||||
|
||||
Connections are not easy though, since this speaker is meant to have
|
||||
wires soldered to its pads, but we used 2x [castellated][2]
|
||||
(half-round plated holes) pads with a placement just over the speaker
|
||||
pads that enables manual soldering between the speaker and the PCB
|
||||
with a solder blob.
|
||||
|
||||
## Schematic
|
||||
|
||||
The audio schematic is simple, as the Allwinner V3s already
|
||||
contains an analog stereo audio codec (coder/decoder): we only have to
|
||||
take one of its headphone output channel (left or right) and feed it
|
||||
to a mono audio amplifier.
|
||||
|
||||
We chose the [Diodes Inc. PAM8301][3] chip because of its cheap price,
|
||||
good availability, its more than sufficient output power of 1.5W and
|
||||
its filterless operation, meaning that no bulky series capacitor is
|
||||
required to drive the speaker.
|
||||
|
||||
Here is the corresponding schematic:
|
||||
|
||||
{.lightbox}
|
||||
|
||||
We chose the right headphone channel HPOUTR that is fed to the audio
|
||||
amplifier **U2** through a coupling capacitor **C3**.
|
||||
|
||||
The audio amplifier /SD shutdown input is driven by one V3s GPIO (PF7
|
||||
on pin 100), with a pull-down resistor **R2** to disable the amplifier
|
||||
by default.
|
||||
|
||||
The audio amplifier power supply is filtered using a ferrite bead
|
||||
**L1** in order to eliminate high-frequency digital noise, and
|
||||
decoupled by 2 capacitors **C4** and **C5**, as recommended in the
|
||||
device datasheet.
|
||||
|
||||
The speaker **SP1** is driven in differential mode in order to get the
|
||||
maximum voltage swing and thus the maximum power available for a given
|
||||
output current.
|
||||
|
||||
Two ESD protection TVS diodes **D13** and **D14** are added, since the
|
||||
speaker may be accessible to the user through the enclosure grid in
|
||||
front of the speaker.
|
||||
|
||||
[1]: https://www.cui.com/product/resource/cdm-10008.pdf
|
||||
[2]: https://www.pcbdirectory.com/community/what-are-castellated-holes-on-a-pcb
|
||||
[3]: https://www.diodes.com/assets/Datasheets/PAM8301.pdf
|
||||
|
||||
--8<--
|
||||
includes/glossary.md
|
||||
--8<--
|
||||
137
docs/developer_guide/hardware_reference/buttons.md
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137
docs/developer_guide/hardware_reference/buttons.md
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|
||||
As a generic game console emulating many classic ones, the FunKey
|
||||
requires numerous buttons:
|
||||
|
||||
- A soft "ON/OFF" button
|
||||
- A "**+**" control pad with "Up", "Down", "Left" and "Right" buttons
|
||||
- A "**X**" control pad with "A", "B", "X" and "Y" buttons
|
||||
- "Start" and a "Fn" buttons
|
||||
- At least L1 and R1 shoulder buttons
|
||||
|
||||
As can be seen in the page on the [PMIC][1], the soft "ON/OFF" button
|
||||
is directly connected to the power management chip, so we are left
|
||||
with 4 + 4 + 2 = 12 buttons for game control.
|
||||
|
||||
After testing tactile domes in our [**FunKey Zero**][2] prototype, we
|
||||
decided to go back to integrated tactile switches, as their placement
|
||||
is much easier using a regular SMT pick & place machine like any other
|
||||
components on the PCB, whereas the separate tactile domes required an
|
||||
adhesive tape to be place manually with less accuracy.
|
||||
|
||||
{: align=left }
|
||||
|
||||
The [Mitsumi BYS-055A1x12][3] is the same footprint (2.5mm x 1.6mm x
|
||||
0.55mm) as the more expensive Panasonic EVBBBxAAB00 tactile switches,
|
||||
with a 1.2N actuating force for the "**+**" and "**X**" pads, and a
|
||||
1.6N actuating force for the "Start", "Fn" and "ON/OFF" buttons. We
|
||||
found these actuating force the best match to provide a good feedback
|
||||
to the user.
|
||||
|
||||
{: align=left }
|
||||
|
||||
For the rear left and right shoulder buttons, we exeperimented several
|
||||
models between PCBA rev. C, D and E, until we eventually decided for a
|
||||
[replacement for the expensive Panasonic EVP-AEBB2A-1][4]:
|
||||
|
||||
This one as an actuating force of 1.6N.
|
||||
|
||||
## GPIO Requirements
|
||||
|
||||
The Allwinner v3s CPU comes in a large 128-pin TQFP package, with a
|
||||
lot of exposed (51!) GPIO pins:
|
||||
|
||||
- PB0 to PB9 (10)
|
||||
- PC0 to PC3 (4)
|
||||
- PE0 to PE24 (25)
|
||||
- PF0 to PF5 (6)
|
||||
- PG0 to PG5 (6)
|
||||
|
||||
The FunKey specializes some of them for specific interfaces like
|
||||
SDCard, PWM, SPI and I2C buses, console UART, but most of them are
|
||||
left available for I/Os.
|
||||
|
||||
## GPIO Expander
|
||||
|
||||
But for the **FunKey S** device and given the small PCB size, wiring
|
||||
all the buttons directly to the V3s puts a lot of constraints on the
|
||||
PCB routing, at such a point that we decided to use a dedicated I2C
|
||||
GPIO expander chip to relieve the burden from the main V3s CPU.
|
||||
|
||||
We use a common chip for this purpose, that is well supported in the
|
||||
Linux kernel: the [NXP PCAL6416AHF.128][5]. It is marketed as a
|
||||
"low-voltage translating 16-bit I2C-bus/SMBus I/O expander with
|
||||
interrupt output, reset, and configuration registers" that just
|
||||
matches exactly our needs.
|
||||
|
||||
As a bonus, this chip features software-controlable internal
|
||||
pull-up/pull-down resistors, so we don't need to add external ones to
|
||||
fix the defaut button states.
|
||||
|
||||
The connection with the V3s CPU is achieved using standard I2C clock
|
||||
(SCL) and data (SDA) signals, plus an additional IRQ signal driven by
|
||||
the I/O expander when pre-programmed conditions are met, such as a key
|
||||
press / release event. A RESET signal is used to initialize the chip
|
||||
when required.
|
||||
|
||||
## Schematics
|
||||
|
||||
Here is the corresponding main schematic for the buttons:
|
||||
|
||||
{.lightbox}
|
||||
|
||||
The main component is of course the I/O expander **U1**, with the
|
||||
control signals to the CPU/PMIC on the north side.
|
||||
|
||||
The chip's /INT signal is pulled up to the +3V3 power supply by the
|
||||
resistor **R1**, such that the active-low interrupt signal is disabled
|
||||
by default.
|
||||
|
||||
The I/O expander chip features 2 separate power supplies VDD and VDDP
|
||||
for the core and peripheral respectively, each decoupled by a bulk
|
||||
capacitor **C1** and **C2**.
|
||||
|
||||
Except for the GPIO I/Os, the only remaining pin is the ADDR pin 18
|
||||
which provides the I2C address LSB bit, so that you can address 2
|
||||
PCAL6416AHF.128 chips on the same I2C bus by wiring this pin
|
||||
differently.
|
||||
|
||||
!!! tip
|
||||
|
||||
One oddity is that the pin 6 (P0_5) is connected to the /RESET
|
||||
signal: it is a routing trick to get this signal to go through
|
||||
this pin pad, as it was very difficult to access it otherwise...
|
||||
|
||||
The "Start" and "Select" buttons **S1** and **S2** are 2 low-profile
|
||||
SMT tactile switches, each featuring an ESD protection TVS diode
|
||||
**D8** and **D5**, as these buttons are of course accessible by the
|
||||
user!
|
||||
|
||||
The other buttons are wired in the same fashion:
|
||||
|
||||
{.lightbox}
|
||||
|
||||
The "U", "L", "D", "R", "A", "B", "X" and "Y" buttons **S3**, **S4**,
|
||||
**S5**, **S6**, **S8**, **S9**, **S10** and **S11** are of the same
|
||||
kind and also have a respective TVS diodes **D2**, **D3**, **D4**,
|
||||
**D5**, **D6**, **D7**, **D8**, **D9**, **D10** and **D11**.
|
||||
|
||||
The left (**S12**) and right (**S7**) shoulder buttons are right angle
|
||||
SMT tactile buttons, with their TVS diode **D1** and **D12**.
|
||||
|
||||
## Benefit
|
||||
|
||||
The main advantage of this solutions is that the 12 signals to wire
|
||||
the buttons to the CPU are replaced by only 4 signals, from which 3
|
||||
are shared with the other I2C peripherals (the PMIC) on the bus.
|
||||
|
||||
It is then much easier to route this dense PCB by delegating the
|
||||
button GPIO handling to a satellite chip.
|
||||
|
||||
[1]: /developers/hardware/power/pmic
|
||||
[2]: https://hackaday.io/project/134065
|
||||
[3]: https://github.com/FunKey-Project/FunKey-S-Hardware/blob/master/Datasheets/Replacement%20EVP-BB1AAB000-(Operating%20force%20120GF%EF%BC%89.pdf
|
||||
[4]: https://github.com/FunKey-Project/FunKey-S-Hardware/blob/master/Datasheets/replacement%20EVP-AEBB2A-1.pdf
|
||||
[5]: https://www.nxp.com/docs/en/data-sheet/PCAL6416A.pdf
|
||||
|
||||
--8<--
|
||||
includes/glossary.md
|
||||
--8<--
|
||||
223
docs/developer_guide/hardware_reference/cpu.md
Normal file
223
docs/developer_guide/hardware_reference/cpu.md
Normal file
@@ -0,0 +1,223 @@
|
||||
The main part in the **FunKey S** device is of course its CPU.
|
||||
|
||||
As discussed in the [Design Constraints section][1], a CPU with
|
||||
external DRAM chips would take too much real-estate on the PCB, so we
|
||||
had to find a CPU with integrated DRAM.
|
||||
|
||||
There are [several options][2] for integrating RAM in a SoC:
|
||||
|
||||
- use SRAM: not possible because of the small amount of memory
|
||||
available (64Mbit max.)
|
||||
|
||||
- embedded DRAM on the same chip: This is the solution used in the
|
||||
[Apple M1 chip][3], but this chip is not available for retail and
|
||||
no other solutions seems readily available
|
||||
|
||||
- Stacked Chip-on-Chip (PoP): This is the solution used on some
|
||||
Raspberry Pi boards, but this solution is only available for custom
|
||||
designs, with minimum order quantities not compatible with the
|
||||
**FunKey S** low volumes
|
||||
|
||||
- DRAM die in SiP: with capacities ranging from 64Mbit to 1Gbit
|
||||
|
||||
We found only 2 manufacturers providing the last option:
|
||||
[Microchip][4] and [Allwinner Technology][5]. Microchip solutions are
|
||||
too limited in term of CPU power for our needs (ARM926EJ-S or Cortex
|
||||
A5), so we did not consider them.
|
||||
|
||||
And with the exception of the mostly similar Allwinner S3 CPU which
|
||||
features the same characteristics but with 128MB DDR3 DRAM in an
|
||||
FBGA234 package, the [Allwinner V3s][6] is the CPU with integrated
|
||||
DRAM having the highest memory capacity (512Mbit / 64MB DDR2 DRAM):
|
||||
|
||||
|
||||
|
||||
Despite its larger package size (16mm x 16mm vs. 11mm x 11mm), we
|
||||
selected the V3s over the S3 because of its better availability and
|
||||
ease of soldering of the LQFP128 over the FBGA234 package for the
|
||||
prototypes.
|
||||
|
||||
The V3s features a rather powerful single-core ARM Cortex A7-A clocked
|
||||
@ 1.2GHz with an additional Vector Floating Point Version 4 (vfpv4)
|
||||
FPU extension and an SIMD NEON architecture with a 32 × 64-bit
|
||||
register file and 64-bit ALU, but unfortunately no GPU or 2D graphic
|
||||
engine containing a hardware scaler that could be extremely useful for
|
||||
the retro-gaming emulators.
|
||||
|
||||
As a bonus, as the V3s is based on an ARM Cortex A7-A low-power
|
||||
architecture, it also features a low power consumption which is
|
||||
required by our battery operation.
|
||||
|
||||
These characteristics do not look very impressive compared to a
|
||||
Raspberry Pi for example, but using many optimizations and after
|
||||
running many tests, we found them nevertheless satisfactory for our
|
||||
purpose.
|
||||
|
||||
## CPU Schematics
|
||||
|
||||
Here is the part of the schematics corresponding to the CPU core:
|
||||
|
||||
{.lightbox}
|
||||
|
||||
## SoC Blocks
|
||||
|
||||
As can be seen, there is not much besides the CPU chip **U3**
|
||||
itself... The CPU is in fact a SoC (System on Chip) containing a
|
||||
collection of built-in peripheral and memory blocks along with the CPU
|
||||
itself:
|
||||
|
||||
- the LCD / DSi display peripheral
|
||||
|
||||
- the GPIO port G / SDC1 (SD Card #1) interface
|
||||
|
||||
- the AUDIO codec
|
||||
|
||||
- the LRADC0 (Low-Resolution Analog to Digital Converter)
|
||||
|
||||
- the USB OTG controller
|
||||
|
||||
- the GPIO port F / SDC0 (SD Card #0) / UART0 interface
|
||||
|
||||
- the RTC (Real Time Clock) timer
|
||||
|
||||
- the EPHY (Ethernet PHYsical) interface
|
||||
|
||||
- the MIPI CSi camera interface
|
||||
|
||||
- the built-in 64 MB DDR2 DRAM
|
||||
|
||||
- the GPIO port C / SPI interface
|
||||
|
||||
- the GPIO port B / UART2 / PWM0 / PWM1 / TWI0 (I2C #0) / TWI1 (I2C
|
||||
#1)
|
||||
|
||||
Among these, the FunKey device only uses a few blocks:
|
||||
|
||||
- AUDIO
|
||||
|
||||
- USB (as device only)
|
||||
|
||||
- SDC0 (for SD Card)
|
||||
|
||||
- RTC
|
||||
|
||||
- DRAM
|
||||
|
||||
- SPI (for the LCD screen)
|
||||
|
||||
- PWM0 (for backlight)
|
||||
|
||||
- TWI0 (for I2C bus to control the GPIO expander and power management
|
||||
chips)
|
||||
|
||||
- A couple of GPIOs to power the audio power amplifier and get
|
||||
feedback interrupt signals from the the GPIO expander and power
|
||||
management chips
|
||||
|
||||
## CPU Power Supplies
|
||||
|
||||
What is remarkable though is that the V3s requires a lot of different
|
||||
voltages for its power supply:
|
||||
|
||||
- +3V3 for the I/O power supply
|
||||
- +3V3_AO for the Always-On power supply (RTC timer)
|
||||
- +3V0 for analog power supply
|
||||
- +1V8 for the DDR2 DRAM power supply
|
||||
- +1V25 for the core power supply
|
||||
|
||||
This profusion of different power supplies as well as the high power
|
||||
drawn by some of them (1.2A for +3V3, 1.6A for +1.25V) requires a
|
||||
sophisticated power management that will be detailed further.
|
||||
|
||||
## LRADC0
|
||||
|
||||
The LRADC0 (Low-Resolution Analog to Digital Converter #0) is designed
|
||||
to measure the voltage of a resistor ladder switched by keyboard keys:
|
||||
this single input is thus in theory able to manage a keyboard of up to
|
||||
10 keys @ 250 Hz.
|
||||
|
||||
Unfortunately, the FunKey has 12 keys (U/D/L/R, A/B/X/Y, RR/RL, Start
|
||||
and Fn), and the resulting key detection accuracy is not compatible
|
||||
with a gaming usage because of long term stability problems. This is
|
||||
the reason why it is not used in the FunKey and just terminated by a
|
||||
proper low-pass filter **R6**/**C9** to avoid picking up noise
|
||||
glitches.
|
||||
|
||||
## SD Card
|
||||
|
||||
The SD Card interface is almost a direct connection between the chip
|
||||
and the dedicated SD Card connector. Only a single series resistor
|
||||
**R8** is required on the high-speed clock line in order to [prevent
|
||||
ringing][7].
|
||||
|
||||
## Crystals
|
||||
|
||||
The V3s chips requires 2 crystals:
|
||||
|
||||
- one low-frequency [32.768 kHz crystal][8] **Y1** for the RTC clock
|
||||
|
||||
- one high-frequency [24 MHz crystal][9] **Y2** for deriving the 1.2
|
||||
GHz clock
|
||||
|
||||
The 24 MHz crystal is used by an internal oscillator to lock the phase
|
||||
of the 1.2 GHz oscillator using a PLL (Phase-Locked Loop).
|
||||
|
||||
The 32.768 kHz crystal is used by another internal oscillator to tick
|
||||
the RTC (Real-Time Clock) at a standard watch frequency.
|
||||
|
||||
These crystals require 2 load capacitors each (**C12**/**C13** and
|
||||
**C14**/**C15** respectively) in order to guarantee that the
|
||||
oscillators still start and work with a comfortable operation margin
|
||||
taking into account voltage, temperature and aging.
|
||||
|
||||
The 32.768 kHz crystal features an additional high-value resistor
|
||||
**R12** in order to limit the internal oscillator's output current and
|
||||
thus reduce further the RTC timer power consumption.
|
||||
|
||||
For more details on crystal oscillator design, please check [this
|
||||
application note from STM][10].
|
||||
|
||||
## DRAM
|
||||
|
||||
The DRAM within the V3s chip is a [DDR2 one][11], meaning that its
|
||||
data lines are clocked using both edges of an up to 400 MHz clock
|
||||
signal.
|
||||
|
||||
At these high frequencies, even short wires have a length that is of
|
||||
the same order of magnitude as the signal's [wavelength][12] and thus
|
||||
each signal should be considered as a [transmission line][13], for
|
||||
which impedance must be matched to avoid signal reflections, requiring
|
||||
termination resistors on the data lines DQx.
|
||||
|
||||
DDR2 or DDR3 DRAMs feature merged drivers and dynamic on-chip
|
||||
termination like this ("VDDQ/2" is labeled "SVREF" in our schematic):
|
||||
|
||||
{.lightbox}
|
||||
|
||||
The V3s DDR2 DRAM has an active termination calibration circuitry and
|
||||
procedure called "_ZQ Calibration_" requiring an accurate 1% 240 Ω
|
||||
resistor **R11** connected internally like this:
|
||||
|
||||
{.lightbox}
|
||||
|
||||
More information on the DDR2 DRAM ZQ Calibration subject can be found
|
||||
in this [Micron Application Note][14].
|
||||
|
||||
[1]: /developers/hardware/design/#design-constraints
|
||||
[2]: https://www.electronicsweekly.com/news/products/memory/how-to-guide-for-on-chip-memory-2012-06/
|
||||
[3]: https://www.apple.com/mac/m1/
|
||||
[4]: https://www.microchip.com/design-centers/32-bit-mpus/sip-som/system-in-package
|
||||
[5]: https://www.allwinnertech.com/
|
||||
[6]: https://linux-sunxi.org/images/f/f5/Allwinner_V3_Datasheet_V1.1.pdf
|
||||
[7]: https://electronics.stackexchange.com/questions/7709/why-put-a-resistor-in-series-with-signal-line
|
||||
[8]: https://github.com/FunKey-Project/FunKey-S-Hardware/blob/master/Datasheets/C55208_FC-12M32.768K12.5PF20PPM_2017-01-16.PDF
|
||||
[9]: https://github.com/FunKey-Project/FunKey-S-Hardware/blob/master/Datasheets/C270485_24MHZ18PF%C2%B110PPM4PIN-20_%2B70%E2%84%83_2018-08-14.PDF
|
||||
[10]: https://www.st.com/content/ccc/resource/technical/document/application_note/c6/eb/5e/11/e3/69/43/eb/CD00221665.pdf/files/CD00221665.pdf/jcr:content/translations/en.CD00221665.pdf
|
||||
[11]: https://en.wikipedia.org/wiki/DDR2_SDRAM
|
||||
[12]: https://en.wikipedia.org/wiki/Wavelength
|
||||
[13]: https://en.wikipedia.org/wiki/Transmission_line
|
||||
[14]: https://www.micron.com/-/media/client/global/Documents/Products/Technical%20Note/DRAM/TN4102.pdf
|
||||
|
||||
--8<--
|
||||
includes/glossary.md
|
||||
--8<--
|
||||
82
docs/developer_guide/hardware_reference/index.md
Normal file
82
docs/developer_guide/hardware_reference/index.md
Normal file
@@ -0,0 +1,82 @@
|
||||
The **FunKey S** is the world's smallest foldable retro-gaming console.
|
||||
|
||||
Holding a world's record is great, but we wanted a device that was
|
||||
_actually_ playable and that still could be attached to a keychain.
|
||||
|
||||
Reaching this goal required more than just the usual job to shrink
|
||||
everything you can: it required a radical change in the design itself.
|
||||
|
||||
## Foldable Design
|
||||
|
||||
The idea to use a foldable clamshell design came up rapidly as the
|
||||
only way to get _both_ a small form factor when closed, and offer the
|
||||
largest screen and keypads while playing.
|
||||
|
||||
But this solution also brings a lot of challenges, as the required
|
||||
hinge make connections between the 2 halfs of the shell more
|
||||
difficult.
|
||||
|
||||
However, this has been done before in the classic GameBoy Advanced SP,
|
||||
or in many clamshell cellphones from some years ago, so why can't we?
|
||||
|
||||
## Design Goals
|
||||
|
||||
Passed this first design decision, we fixed ourselves some additional
|
||||
goals in order to provide the user a good gaming experience:
|
||||
|
||||
- have a CPU that is powerful enough to be able to emulate most
|
||||
retro-gaming consoles, up to the PS1
|
||||
|
||||
- have a good quality screen with a resolution large enough to
|
||||
display even the games featuring small texts
|
||||
|
||||
- have a set of keys and pads large enough and complete enough to be
|
||||
able to play comfortably
|
||||
|
||||
- have a built-in audio capability (who can play without sound?)
|
||||
|
||||
- be able for a 6-year old child to add games and emulators
|
||||
|
||||
- as an extremely nomad device, be able to stop playing just by
|
||||
closing the console, and restart when opening it just where you
|
||||
left (we call this feature "**_Instant Play_**")
|
||||
|
||||
## Design Constraints
|
||||
|
||||
Besides the constraint brought by the hinge listed above, the main
|
||||
difficulty is due to the maximum device dimensions that should not
|
||||
exceed those of a (large) car key.
|
||||
|
||||
And because of the foldable design, the most constrained dimension is
|
||||
thickness: having a folding screen also means doubling the plastic
|
||||
enclosure around the screen and the other internal parts.
|
||||
|
||||
In order to meet these constraints, we had to take more
|
||||
(heart-breaking) decisions:
|
||||
|
||||
- a CPU with external DRAM chips would take too much real-estate on
|
||||
the PCB, so we had to find a CPU with integrated DRAM
|
||||
|
||||
- an audio Jack would be very difficult to integrate, so we decided
|
||||
to use an internal speaker instead
|
||||
|
||||
- an USB C connector is too thick and large, so we used a Micro USB
|
||||
connector instead
|
||||
|
||||
- a Micro SD connector with external access would be too large, as
|
||||
the required "push/push" mechanism, plus the mechanical design to
|
||||
make sure the card does not get loose make the solution much larger
|
||||
|
||||
- because of real-estate constraints on the PCB as well as power
|
||||
consumption constraints, we decided to not integrate Wi-Fi and/or
|
||||
Bluetooth
|
||||
|
||||
- the only keypad technology able to meet our thickness goal is using
|
||||
integrated tactile switches
|
||||
|
||||
- battery capacity had to be adjusted to the maximum available
|
||||
internal volume, using standard battery dimensions
|
||||
|
||||
--8<--
|
||||
includes/glossary.md
|
||||
--8<--
|
||||
42
docs/developer_guide/hardware_reference/magnetic_switch.md
Normal file
42
docs/developer_guide/hardware_reference/magnetic_switch.md
Normal file
@@ -0,0 +1,42 @@
|
||||
The **FunKey S** features no ON/OFF switch. Instead, a small magnet
|
||||
placed near the LCD screen in the lid is detected using a magnetic
|
||||
sensor that is placed in front of it when the lid is closed.
|
||||
|
||||
The magnetic sensor controls the PMIC N_OE (Negative logic Output
|
||||
Enable) input, which turns off all voltage rails except the +3.3V
|
||||
Always On when the signal is at the high level.
|
||||
|
||||
We thus need a sensor that will close when a magnetic field is
|
||||
detected, and in order to reduce power consumption when the **FunKey
|
||||
S** is turned off and preserve its battery when stored on a shelf, it
|
||||
should be a fully passive device. This rules out magnetic Hall effect
|
||||
sensors, wich require some power for their operation.
|
||||
|
||||
The only practical solution is to use a "Reed switch", which is a
|
||||
relatively thin flexible piece of metal inside the switch envelope
|
||||
that is sensitive to a magnetic field, which opens or closes a contact
|
||||
accordingly.
|
||||
|
||||
Most of the Reed switch available are made of a tiny glass tube, which
|
||||
is rather fragile and may break if the device falls on the floor,
|
||||
something quite usual for a keychain...
|
||||
|
||||
We found only a unique plastic-molded model which almost meets our
|
||||
low-profile requirements of 1.5 mm (1.6 mm height!): the [Standex
|
||||
Meder MK24][1].
|
||||
|
||||
Here is the corresponding schematics, already covered in the PMIC
|
||||
discussion:
|
||||
|
||||
{.lightbox}
|
||||
|
||||
The global PMIC chip enable signal N_OE is activated by default
|
||||
through a 47kΩ resistor **R17** to GND, but the magnetic Reed switch
|
||||
**S14** can disable it by forcing its level to +VOUT, with a filter
|
||||
capacitor **C83**.
|
||||
|
||||
[1]: https://github.com/FunKey-Project/FunKey-S-Hardware/blob/master/Datasheets/MK24_V02.pdf
|
||||
|
||||
--8<--
|
||||
includes/glossary.md
|
||||
--8<--
|
||||
122
docs/developer_guide/hardware_reference/power/decoupling.md
Normal file
122
docs/developer_guide/hardware_reference/power/decoupling.md
Normal file
@@ -0,0 +1,122 @@
|
||||
## Capacitor Usage
|
||||
|
||||
So far, we already encountered capacitors for many different usages:
|
||||
|
||||
### Load Capacitors
|
||||
|
||||
We have seen load capacitors used with the 2 crystals in the
|
||||
discussion about [CPU][1].
|
||||
|
||||
A quartz crystal always provides both series and parallel resonance,
|
||||
the series resonance being a few kilohertz lower than the parallel
|
||||
one.
|
||||
|
||||
Crystals below 30 MHz like ours are generally operated between series
|
||||
and parallel resonance, which means that the crystal appears as an
|
||||
inductive reactance in operation, this inductance forming a
|
||||
**parallel resonant circuit** with externally connected parallel
|
||||
"load" capacitance. Any small additional capacitance added in parallel
|
||||
with the crystal pulls the frequency lower in the range between the
|
||||
series and parallel resonance frequencies, insuring crystal startup
|
||||
and stable operation.
|
||||
|
||||
For modern circuits, these load capacitors have a typical small value
|
||||
< 20 pF.
|
||||
|
||||
### Bulk Capacitors
|
||||
|
||||
Bulk capacitors are used to prevent a power supply from dropping too
|
||||
far during the periods when current is not available. At the same
|
||||
time, they help to reduce the power supply voltage ripples by
|
||||
smoothing their output voltage.
|
||||
|
||||
Many such capacitors are used at both the input and output of the
|
||||
numerous linear and switched mode power supplies in the [PMIC
|
||||
discussion][2].
|
||||
|
||||
The main bulk capacitor value is generally high (some µF), but there
|
||||
may be smaller parallel capacitors added for stability.
|
||||
|
||||
### Coupling Capacitors
|
||||
|
||||
As you probably know, capacitors are made of 2 parallel conductive
|
||||
electrodes separated by a (thin) isolating dielectric material (even
|
||||
if these electrodes are rolled or layered to reduce the component
|
||||
size). Thus by construction, no DC (Direct Current) can flow from one
|
||||
electrode to the other, but by influence using the electric field, AC
|
||||
(Alternative Current) still can go through. This is how coupling
|
||||
capacitors are used to link 2 circuits while removing any DC bias
|
||||
voltage on one side or the other of the capacitor.
|
||||
|
||||
We use such a coupling capacitor in the [Audio schematic
|
||||
description][3] for feeding the audio power amplifier from the CPU
|
||||
audio output.
|
||||
|
||||
### Filter Capacitors
|
||||
|
||||
We have seen many examples where capacitors are used within passive
|
||||
filter circuits along with resistors or inductors, mainly to remove
|
||||
unwanted frequencies from a power supply or a signal.
|
||||
|
||||
### Decoupling (Bypass) Capacitors
|
||||
|
||||
We use some decoupling capacitors in the [buttons circuit][4].
|
||||
|
||||
Active components such as transistors and chips are connected to their
|
||||
power supplies through conductors featuring a (small) common impedance
|
||||
made up of complex (resistive, capacitive and inductive)
|
||||
value. Because of these parasitic components, a device that suddenly
|
||||
draws some current in spikes will generate a drop in its voltage power
|
||||
supply. If many devices are sharing the same power supply and
|
||||
impedance, the state of one device will be coupled to the other ones
|
||||
through the common impedance of the power supply conductors and may
|
||||
affect their operation.
|
||||
|
||||
In order to decouple the devices, capacitors placed as close as
|
||||
possible to the device power supply input pins are used, which act as
|
||||
local energy storage. These capacitors are also named "bypass
|
||||
capacitors" as they shunt transient energy from the power supplies
|
||||
past the device to be decoupled, right to the GND return path.
|
||||
|
||||
There may be different capacitors values placed on the same power
|
||||
supply pins in order to filter transients at different frequencies:
|
||||
the bigger the capacitor value, the lower the frequency. A typical
|
||||
value is 100 nF, and values from 1 µF to 10 µF are used for lower
|
||||
frequencies and / or higher current draws, while lower values of a few
|
||||
nF are used for filtering higher frequencies.
|
||||
|
||||
In essence, decoupling capacitors are not very different in their
|
||||
function from bulk capacitors: the only difference is one of scale,
|
||||
both of current and of transient duration. Bulk capacitors deal with
|
||||
large currents and periods of 10s of ms, whereas decoupling capacitors
|
||||
are used for much lower currents and much briefer periods (typically
|
||||
10s of ns for TTL or CMOS devices) .
|
||||
|
||||
## Schematics
|
||||
|
||||
The last part of the FunKey schematics merely contains only decoupling
|
||||
capacitors:
|
||||
|
||||
{.lightbox}
|
||||
|
||||
One exception is the Allwinner V3s CPU HPR/HPL circuit which features
|
||||
an RC-to-ground circuit between the amplifier and the preamplifier
|
||||
input with the resistor **R27** and capacitors **C79** and **C81**, as
|
||||
recommended in the [V3s hardware design guide][5].
|
||||
|
||||
The only other remarkable point left in this schematic is the resistor
|
||||
divider **R25**/**R28** which provides a reference voltage at half the
|
||||
DRAM power supply voltage level, which is used for the integrated DDR2
|
||||
DRAM merged drivers and dynamic on-chip termination already discussed
|
||||
at the end of the previous [CPU schematic description][6].
|
||||
|
||||
[1]: /developers/hardware/cpu
|
||||
[2]: /developers/hardware/power/pmic
|
||||
[3]: /developers/hardware/audio
|
||||
[4]: /developers/hardware/buttons
|
||||
[5]: https://github.com/Squonk42/V3s_Documentation/blob/master/V3s%20hardware%20design%20guide%20V1.0_20150519%20EN%20Non%20Official.pdf
|
||||
[6]: /developers/hardware/cpu
|
||||
|
||||
--8<--
|
||||
includes/glossary.md
|
||||
--8<--
|
||||
46
docs/developer_guide/hardware_reference/power/dram_power.md
Normal file
46
docs/developer_guide/hardware_reference/power/dram_power.md
Normal file
@@ -0,0 +1,46 @@
|
||||
A separate [Sylergy SY8088][1] Buck DC/DC SMPS chip is used to provide
|
||||
the DDR2 +1V8 DDR2 DRAM power.
|
||||
|
||||
This is because the AXP20x is originally the PMU (Power Management
|
||||
Unit) used by most Allwinner SoCs (A10, A13 and A20), which do not
|
||||
integrate SDRAM, so the board designer has a wide choice of memory
|
||||
option: DDR2, DDR3, DDR3L, LPDDR3, LPDDR4 with various voltage
|
||||
requirements.
|
||||
|
||||
But no specific PMIC was created for the Allwinner V3s used in the
|
||||
FunKey device which however integrates a fixed SiP (System In Package)
|
||||
512Mbit (64MB) DDR2 SDRAM.
|
||||
|
||||
We thus have to design a separate SMPS (DC-DC) power supply for
|
||||
providing the +1.8V 1A required for the DDR2 DRAM power supply.
|
||||
|
||||
For this purpose, we followed closely the [Allwinner Reference
|
||||
Design][2].
|
||||
|
||||
Here is the corresponding DRAM Power schematics:
|
||||
|
||||
{.lightbox}
|
||||
|
||||
Nothing very fancy here: the SMPS chip **U4** has its required input
|
||||
filter capacitor **C37** and output capacitors **C65** and **C73**.
|
||||
|
||||
The low-profile ferrite-core power inductor **L6** (rated with a
|
||||
saturation current of 1.76A and low < 0.1 Ω resistance) provides the
|
||||
DC-DC energy storage element.
|
||||
|
||||
The **R20**/**R23** precision voltage divider provides the required
|
||||
+0.6V feedback voltage from the +1.8V output voltage by having a 1/3
|
||||
resistor ratio.
|
||||
|
||||
The last component is a pull-up resistor **R19** which ties the SMPS
|
||||
chip enable input to its active level permanently. The pull-up voltage
|
||||
is +3.0V (just as in the original reference design), probably as it is
|
||||
the next higher voltage available, in order to limit the current in it
|
||||
to its lowest possible value.
|
||||
|
||||
[1]: https://github.com/FunKey-Project/FunKey-S-Hardware/blob/master/Datasheets/C79313_SY8088AAC_2017-03-29.PDF
|
||||
[2]: https://github.com/Squonk42/V3s_Documentation/blob/master/V3S_CDR_STD_V1_0_20150514.pdf
|
||||
|
||||
--8<--
|
||||
includes/glossary.md
|
||||
--8<--
|
||||
@@ -0,0 +1,113 @@
|
||||
Looking back at the section on the [CPU schematics][1], the **FunKey
|
||||
S** device clearly needs a sophisticated power supply in order to
|
||||
fulfill the CPU power requirements. They are recalled below, along
|
||||
with the maximum current requirements found in the [Allwinner V3s
|
||||
reference design][2] (page 3):
|
||||
|
||||
- +3.3V / 1.2A for the I/O power supply
|
||||
- +3.3V_AO / 30 mA for the Always-On power supply (RTC timer)
|
||||
- +3.0V / 200 mA for the analog power supply
|
||||
- +1.8V / 1A for the DDR2 DRAM power supply
|
||||
- +1.25V / 1.6 A for the core power supply
|
||||
|
||||
But why in the first place are there so many different power supply
|
||||
voltages required?
|
||||
|
||||
## Power Efficiency
|
||||
|
||||
A first answer is: for better power efficiency.
|
||||
|
||||
As P = U x I (Electrical power is the product of voltage level by
|
||||
current intensity), you can reduce power by decreasing the required
|
||||
current or by reducing the operating voltage. Assuming you already do
|
||||
your best to reduce the required current, you can still reduce power
|
||||
by reducing the voltage.
|
||||
|
||||
## Reducing Power Supply Voltage
|
||||
|
||||
### Voltage Drop
|
||||
|
||||
But how far can you go? Over long distance, you have the voltage drop
|
||||
from the conductor linear resistance, but this effect can be neglected
|
||||
for small boards.
|
||||
|
||||
### Noise Margin
|
||||
|
||||
You have inductive and capacitive coupling between conductive wires
|
||||
and planes too, but within a PCB, these coupling only have a limited
|
||||
direct effect on voltage. However, these coupling play a role in that
|
||||
they will pick up external electromagnetic noise from the surroundings
|
||||
and inject it into the circuit.
|
||||
|
||||
And with digital circuits, a critical limit when lowering the
|
||||
operating voltage is the "noise margin" or difference in absolute
|
||||
voltage levels between a logical '0' and logical '1', which determines
|
||||
the maximum amplitude of spurious voltage spikes that a conductor can
|
||||
pick up that will trigger an erroneous logic level change.
|
||||
|
||||
This phenomenon mostly depends on the circuit scale: a long-distance
|
||||
circuit between boards will require higher voltages (typically +12V or
|
||||
+24V) to limit this effect, whereas a circuit between boards a few
|
||||
meters apart or using through-hole chips on the same board wile
|
||||
require a lower voltage (typically +5V like the old Arduinos). Using
|
||||
SMT chips will allow even smaller boards and lower voltages (+3.3V is
|
||||
typical today), and with wires running on the same silicon die, it is
|
||||
possible to go down to +1.2V, given the current technological limits.
|
||||
|
||||
### Voltage Swing
|
||||
|
||||
There are other reasons why you should try to minimize voltages: the
|
||||
core CPU for example needs to run as fast as possible, and lowering
|
||||
its operating voltage will shorten the signal rise and fall duration
|
||||
as the voltage swing is reduced.
|
||||
|
||||
## Other Power Supply Considerations
|
||||
|
||||
Besides reducing the operating voltage, there are other considerations
|
||||
that may push to multiply the number of power supplies in a design:
|
||||
|
||||
### Quiescent Current
|
||||
|
||||
As for power supply used for standby operation providing small
|
||||
currents, a very-low leakage current ("quiescent current") is required
|
||||
as it can no longer be neglected compared to the current required by
|
||||
the light load and even more importantly because this current
|
||||
consumption is permanent.
|
||||
|
||||
### Ripple Voltage
|
||||
|
||||
For sensitive circuits such as ADCs (Analog to Digital Converters) or
|
||||
PLLs (Phase-Locked Loops) which rely on comparing very small voltage
|
||||
differences, a "clean" power supply featuring very low ripple voltage
|
||||
amplitude is required to achieve a good resolution and/or
|
||||
accuracy. This characteristic is only possible to obtain using LDOs
|
||||
and not SMPS, and the figure to pay attention to is then the PSRR
|
||||
(Power Supply Rejection Ratio) or how much a variation in the input
|
||||
voltage will affect the output voltage: the higher, the better! A
|
||||
value > 50 dB is a good starting point.
|
||||
|
||||
## Application to the FunKey Design
|
||||
|
||||
Based on these considerations, it is now clear that each V3s power
|
||||
supply voltage has a good reason to exist:
|
||||
|
||||
- +3.3V / 1.2A is used for powering the I/Os to connect between chips
|
||||
on the board. Given the required current, a SMPS is required for
|
||||
reaching a good efficiency
|
||||
- +3.3V_AO / 30 mA for the Always-On power supply (RTC timer)
|
||||
requires a low quiescent-current, so an LDO is used
|
||||
- +3.0V / 200 mA for the analog power supply also requires an LDO,
|
||||
this time to minimize the ripple voltage
|
||||
- +1.8V / 1A for the DDR2 DRAM power supply: this strange voltage
|
||||
level is typical for DDR2 DRAM memory chips, and is the result of
|
||||
driving the large memory array inside the chip
|
||||
- +1.25V / 1.6 A for powering the CPU core to minimize the voltage
|
||||
swing and increase the possible CPU frequency. Given the required
|
||||
current, a SMPS is required for reaching a good efficiency, too
|
||||
|
||||
[1]: /developers/hardware/cpu#cpu-schematics
|
||||
[2]: https://github.com/Squonk42/V3s_Documentation/blob/master/V3S_CDR_STD_V1_0_20150514.pdf
|
||||
|
||||
--8<--
|
||||
includes/glossary.md
|
||||
--8<--
|
||||
298
docs/developer_guide/hardware_reference/power/pmic.md
Normal file
298
docs/developer_guide/hardware_reference/power/pmic.md
Normal file
@@ -0,0 +1,298 @@
|
||||
From the previous section, we can summarize the V3s power supply
|
||||
requirements to:
|
||||
|
||||
- SMPS for +3.3V / 1.2A for the I/O power supply
|
||||
- LDO for +3.3V_AO / 30 mA for the Always-On power supply (RTC timer)
|
||||
- LDO for +3.0V / 200 mA for the analog power supply
|
||||
- SMPS for +1.8V / 1A for the DDR2 DRAM power supply
|
||||
- SMPS for +1.25V / 1.6 A for the core power supply
|
||||
|
||||
On the [LicheePi Zero board][1] used in our **[FunKey Zero][2]**
|
||||
prototype, a triple SMPS [EA3036][3] is used for generating these
|
||||
+3.3V, +1.8V and +1.2V voltages, with an additional [XC6206][4] LDO
|
||||
for the +3.0V (the +3.3V Always On is connected directly to
|
||||
+3.3V). Although compact (the EA3036 is a tiny 3 mm x 3 mm QFN20
|
||||
package), this solution is not ideal as it does not provide a battery
|
||||
charger and monitoring capability, which is a requirement for the
|
||||
**FunKey S** device.
|
||||
|
||||
## PMICs
|
||||
|
||||
As it is generally the case with such a complex SoC requiring multiple
|
||||
voltages, high current and proper voltage sequencing, all major
|
||||
manufacturers provide dedicated companion chips called PMICs (Power
|
||||
Management Integrated Circuits), in charge of these tasks. Allwinner
|
||||
is not an exception through its sister company [X-Powers][5].
|
||||
|
||||
Their AXP20x products are highly-integrated PMICs that are optimized
|
||||
for applications requiring single-cell Li-battery (Li-Ion/Polymer),
|
||||
multiple output DC-DC converters and LDOs. Here is a block diagram:
|
||||
|
||||
{.lightbox}
|
||||
|
||||
The AXP20x features:
|
||||
|
||||
- A wide choice of input power source, the best source is output as
|
||||
IPSOUT inside the IPS (Intelligent Power Select) block:
|
||||
|
||||
- USB VBUS
|
||||
|
||||
- Battery BAT
|
||||
|
||||
- ACIN wall plug (not used in the **FunKey S**)
|
||||
|
||||
- BACKUP battery (not used in the **FunKey S**)
|
||||
|
||||
- A 1.8A fast PWM battery charger (also called DC/DC1) with battery
|
||||
voltage / current sense and programmable charge indication LED
|
||||
|
||||
- A soft key power-on/off logic with timer (just as in smartphones!)
|
||||
|
||||
- An I2C interface with interrupt signal to communicate with the CPU
|
||||
|
||||
- An optional battery temperature monitoring if the battery is
|
||||
equipped with an NTC resistor (not used in the **FunKey S**)
|
||||
|
||||
- A reference voltage
|
||||
|
||||
- A built-in 12-channel 12 bit ADC that measures various voltages and
|
||||
currents data, as well as feeding an internal Coulomb counter and
|
||||
fuel gauge system (more on this later)
|
||||
|
||||
- A "power OK" output used to generate the global RESET signal for the
|
||||
**FunKey S**
|
||||
|
||||
- 5x GPIOs (not used in the **FunKey S**), GPIO0 can be programmed as
|
||||
LDO5 output
|
||||
|
||||
- 2x DC/DC SMPS DC-DC2 and DC-DC3
|
||||
|
||||
- 5x LDOs (only 2 are used in the **FunKey S**, LDO5 is optionnaly
|
||||
output to GPIO0)
|
||||
|
||||
Looking at their datasheets, it is difficult to tell the difference
|
||||
between the [AXP202][6], [AXP203][7] and [AXP209][8] (any hint
|
||||
welcome!). In the **FunKey S** design, we use an AXP209 because it is
|
||||
the one that comes along with the V3s when you buy it on AliExpress.
|
||||
|
||||
## AXP20x Application Diagram
|
||||
|
||||
For complex dedicated chips like this, the best option is to follow as
|
||||
much as possible the application diagram and reference design given by
|
||||
the manufacturer, as the internals of the chips are seldom fully
|
||||
disclosed, so you need to take their word on some of the external
|
||||
component values to use.
|
||||
|
||||
The [Allwinner V3s Reference Design][9] contains on page 6 the
|
||||
schematics for using an AXP203 to supply the power to a V3s-based
|
||||
dashboard camera design. It follows closely the application diagram
|
||||
provided in the AXP20x datasheets:
|
||||
|
||||
{.lightbox}
|
||||
|
||||
More hints are provided in our self-translated [V3s Hardware Design
|
||||
Guide][10] (page 7) too.
|
||||
|
||||
## PMIC Schematics
|
||||
|
||||
The **FunKey S** device uses all of the **U5** AXP209 integrated SMPS:
|
||||
|
||||
- the PWM charger DC-DC1 for the battery
|
||||
- the DC-DC2 for providing the +1.25 V / 1.6A to the core
|
||||
- the DC-DC3 for providing the +3.3V / 1.2A to the I/Os
|
||||
|
||||
But compared to the sophisticated reference design above, the **FunKey
|
||||
S** device only uses 2 out of the 5 integrated LDOs:
|
||||
|
||||
- LDO1 supplies the +3.3V / 30 mA Always On for the RTC
|
||||
- LDO2 provides the +3.0V / 200 mA for the analog power supply
|
||||
- LDO3 / LDO4 / LDO5 are not used in the **FunKey S**
|
||||
|
||||
Here are the PMIC schematics:
|
||||
|
||||
{.lightbox}
|
||||
|
||||
These schematics may look intimidating and complex, but they are in
|
||||
fact just a collection of simple basic elements, and it is actually
|
||||
very close to the manufacturer-recommended design.
|
||||
|
||||
Here are the details for each PMIC functions, one by one:
|
||||
|
||||
### Power Inputs (East side)
|
||||
|
||||
A wall-plug AC adapter input is not used in the **FunKey S** device,
|
||||
so +VIN is just filtered using C75 on pins 32 and 33.
|
||||
|
||||
The USB power input +VUSB on pin 31 is filtered using **C70**, and the
|
||||
best (between +VUSB and +VBAT) available voltage is output to +VOUT on
|
||||
pins 34 and 35 and filtered using **C78**.
|
||||
|
||||
The BACKUP supply on pin 30 is not used and is left unconnected.
|
||||
|
||||
### Internal Connections (All sides)
|
||||
|
||||
Some AXP20x signals are externally available and should be connected
|
||||
to external components:
|
||||
|
||||
- The BIAS connection on pin 23 is connected to a precision 200k 1%
|
||||
resistor **R22**, as recommended
|
||||
|
||||
- The reference voltage VREF on pin 24 is decoupled with **C64**
|
||||
|
||||
- The +2.5V internal logic voltage VINT on pin 26 is filtered using
|
||||
the recommended value for **C67**
|
||||
|
||||
Additionally, the AXP20x is actually made up of separate flexible
|
||||
blocks that require external interconnections to set their desired
|
||||
operation:
|
||||
|
||||
- All DC/DC inputs (VIN1 on pin 44, VIN2 on pin 7 and VIN3 on pin
|
||||
14), as well as LDO3IN input on pin 40 are connected to the best
|
||||
available voltage +VOUT with filter capacitors **C59**, **C23**,
|
||||
**C30**, and **C69**, respectively
|
||||
|
||||
- LDO1SET on pin 27 is used to set the initial voltage of LDO1, and
|
||||
according to the datasheets, setting it to VINT sets its voltage to
|
||||
the desired +3.3V for the +3.3V Always On power supply
|
||||
|
||||
- OTOH, combined LDO 2 and 4 input LDOIN24 on pin 13 is instead
|
||||
connected to +3.3V in order to minimize the voltage drop for LDO2
|
||||
to generate the +3.0V. Here too, there is a filter capacitor
|
||||
**C34**
|
||||
|
||||
- It is not clear what is the exact function of APS on pin 21 (it is
|
||||
described as "Internal Power Input"), but it must be connected to
|
||||
+VOUT, too
|
||||
|
||||
### DC-DC1 PWM Battery Charger (North East side)
|
||||
|
||||
The battery is connected to J5 (a [2-pin JST 1.0 mm pitch
|
||||
receptacle][11]) and uses **R21** as a precision current sense
|
||||
resistor, with **C53**/**C56**/**C60** filter capacitors and **L5** (a
|
||||
low-profile ferrite-core power inductor rated with a saturation
|
||||
current of 1.2A and low < 0.1 Ω resistance).
|
||||
|
||||
!!! Warning
|
||||
The battery is not protected on the board against reversing
|
||||
polarity, as the model used already contains a built-in
|
||||
protection.
|
||||
|
||||
**R24** is mounted to simulate a battery NTC resistor for measuring
|
||||
temperature, as the chosen LiPo battery does not feature this
|
||||
temperature sensor.
|
||||
|
||||
A user-programmable (through the I2C interface) charge [LED][12]
|
||||
**D30** is provided, with its current-limiting resistor **R26**, as
|
||||
well as a TVS diode **d31** to prevent ESD, as the LED body will be
|
||||
indirectly accessible to user.
|
||||
|
||||
### DC-DC2 +1.25V / 1.6A (West side)
|
||||
|
||||
This SMPS is built around the ferrite core power inductor **L3** and
|
||||
filter capacitors **C26** and **C29**.
|
||||
|
||||
### DC-DC3 +3.3V / 1.2A (South side)
|
||||
|
||||
This SMPS is built around the ferrite core power inductor **L4** and
|
||||
filter capacitors **C39** and **C43**.
|
||||
|
||||
### LDO1 +3.3V Always On 30mA (South East side)
|
||||
|
||||
The LDO output on pin 28 is filtered with capacitor **C72**.
|
||||
|
||||
### LDO2 +3.0V / 200mA (South West side)
|
||||
|
||||
The LDO output on pin 12 is filtered with capacitor **C33**.
|
||||
|
||||
### LDO3 (North side)
|
||||
|
||||
This LDO is not used and its output on pin 41 is nevertheless filtered
|
||||
with a capacitor **C63**.
|
||||
|
||||
### LDO4 (South West side)
|
||||
|
||||
This LDO is not used and its output on pin 11 is nevertheless filtered
|
||||
with a capacitor **C38**.
|
||||
|
||||
### Power Key (North West side)
|
||||
|
||||
The AXP20x features a soft power key with internal short and
|
||||
long-press detection with user-programmable time settings, which
|
||||
enables turning power ON or OFF much like the way it is done in
|
||||
cellular phones.
|
||||
|
||||
Only a few external components are required: the tactile switch
|
||||
**S13**, its ESD protection TVS **D29**, and a low-pass filter **R18**
|
||||
and **C42** for debouncing the switch.
|
||||
|
||||
### I2C Bus (North West side)
|
||||
|
||||
The AXP20x can be externally controlled by the main CPU using the I2C
|
||||
bus on pins 1 and 2. This bus has pull-up resistors to +3.3V **R14**
|
||||
and **R16**, and the IRQ/WAKEUP signal on pin 48 enables warning or
|
||||
waking up the CPU on a selection of AXP20x-generated events, with a
|
||||
pull-up resistor **R13** to +3.3V.
|
||||
|
||||
### GPIOs (South and West sides)
|
||||
|
||||
GPIO0-3 on pins 19, 18, 5 and 3 are not used in the **FunKey S** and
|
||||
are left unconnected.
|
||||
|
||||
### PWROK (South West side)
|
||||
|
||||
The PWROK signal on pin 25 is used to generate the global RESET signal
|
||||
for the whole board, with a pull-up resistor **R15** to the +3.3V
|
||||
Always On power supply and a filter capacitor **C18**.
|
||||
|
||||
### Enable Signals (West side)
|
||||
|
||||
The global chip enable signal N_OE on pin 4 is activated by default
|
||||
through a 47kΩ resistor **R17** to GND, but a magnetic Reed switch
|
||||
**S14** can disable it by forcing its level to +VOUT, with a filter
|
||||
capacitor **C83**. This circuit will be disscused later in the
|
||||
[Magnetic Switch section][13].
|
||||
|
||||
The USB enable signal N_VBUSEN on pin 6 is directly tied to GND to
|
||||
always enable power from the USB bus.
|
||||
|
||||
### Monitoring
|
||||
|
||||
Through the I2C bus and the numerous internal available registers, the
|
||||
AXP20x provides a very fine control of its operation, including many
|
||||
threshold and timing settings, but also many voltage and curent
|
||||
monitoring values.
|
||||
|
||||
### Coulomb Counters / Fuel Gauge
|
||||
|
||||
It is well known that battery discharge voltage curve over time is
|
||||
very flat, making it very difficult to estimate the real
|
||||
charge/discharge state of the battery. Moreover, this state will vary
|
||||
with temperature, load, and aging.
|
||||
|
||||
The only accurate way to monitor the battery status is to actually
|
||||
count the energy that is stored when charging, and the one that is
|
||||
consumed. This particularly important feature is achieved in the
|
||||
AXP20x using a dual Coulomb counter which continuously sums the
|
||||
current intensity over time for monitoring the battery accurate charge
|
||||
and discharge status, with user-defined alert thresholds.
|
||||
|
||||
This fuel gauge is providing the ability to precisely report the
|
||||
remaining battery capacity, just like people are used to with cellular
|
||||
phones.
|
||||
|
||||
[1]: https://licheepizero.us/
|
||||
[2]: https://hackaday.io/project/134065-funkey-zero
|
||||
[3]: http://club.szlcsc.com/article/downFile_D72C44885C60F9F1.html
|
||||
[4]: https://www.torexsemi.com/file/xc6206/XC6206.pdf
|
||||
[5]: http://www.x-powers.com/en.php
|
||||
[6]: http://www.x-powers.com/en.php/Info/down/id/55
|
||||
[7]: https://github.com/Squonk42/V3s_Documentation/raw/master/AXP203_Datasheet_V1.0.pdf
|
||||
[8]: https://github.com/Squonk42/V3s_Documentation/raw/master/AXP209_Datasheet_v1.0en.pdf
|
||||
[9]: https://github.com/Squonk42/V3s_Documentation/blob/master/V3S_CDR_STD_V1_0_20150514.pdf
|
||||
[10]: https://github.com/Squonk42/V3s_Documentation/raw/master/V3s%20hardware%20design%20guide%20V1.0_20150519%20EN%20Non%20Official.pdf
|
||||
[11]: https://github.com/FunKey-Project/FunKey-S-Hardware/blob/master/Datasheets/1811151533_JST-Sales-America-SM02B-SRSS-TB-LF-SN_C160402.pdf
|
||||
[12]: https://github.com/FunKey-Project/FunKey-S-Hardware/blob/master/Datasheets/C165977_%E8%B4%B4%E7%89%87LED%E8%93%9D%E8%89%B2_2018-01-26.PDF
|
||||
[13]: /developers/hardware/magnetic_switch
|
||||
--8<--
|
||||
includes/glossary.md
|
||||
--8<--
|
||||
@@ -0,0 +1,170 @@
|
||||
Simple DC electronic circuits can be powered by directly connecting a
|
||||
battery. However, more complex circuits usually require a constant
|
||||
input voltage for proper operation.
|
||||
|
||||
This page is a small sidetrack to explain the different regulated DC
|
||||
power supply topologies, before looking at the **FunKey S** power
|
||||
supply schematics in details.
|
||||
|
||||
If you are already comfortable with this subject, you can skip this
|
||||
section entirely!
|
||||
|
||||
## Linear Regulators
|
||||
|
||||
The easiest method to achieve a constant voltage viewed from the load
|
||||
despite a varying source voltage is to linearly control the resistance
|
||||
of the regulator in accordance with the load, resulting in a constant
|
||||
output voltage.
|
||||
|
||||
### Shunt Regulator
|
||||
|
||||
The simplest voltage regulator is the [shunt regulator][1], built
|
||||
around a Zener diode which most interesting characteristic is to
|
||||
maintain a constant voltage across itself when the current through it
|
||||
is sufficient to take it into the Zener breakdown region. A simple
|
||||
shunt regulator looks like this:
|
||||
|
||||
|
||||
|
||||
### Series Regulator
|
||||
|
||||
By adding a emitter-follower transistor to the simple shunt regulator,
|
||||
the small base current of the transistor forms a very light load on
|
||||
the Zener, thereby minimizing variation in Zener voltage due to
|
||||
variation in the load, resulting in a better regulation. Here is a
|
||||
schematic for this [series regulator][2]:
|
||||
|
||||
|
||||
|
||||
### Integrated Linear Regulator
|
||||
|
||||
In integrated voltage regulators, the discrete Zener diode is replaced
|
||||
by a more sophisticated (but easier to integrate) circuit built around
|
||||
a resistor divider feeding an operational amplifier, a voltage
|
||||
reference, and a transistor driving the emitter-follower pass
|
||||
transistor:
|
||||
|
||||
|
||||
|
||||
Usually, the pass transistor and its driving transistor are combined
|
||||
into a single Darlington transistor plus a controllable current source
|
||||
like this:
|
||||
|
||||
|
||||
|
||||
### LDO (Low Drop-Out) Regulator
|
||||
|
||||
The above circuit works well, but its drop-out voltage (the difference
|
||||
between the input and output voltage) is rather high because of this
|
||||
transistor cascade, around 1.5V to 2.5V.
|
||||
|
||||
By replacing the emitter-follower Darlington transistor by a PNP
|
||||
transistor in an open collector or open drain topology, the drop-out
|
||||
voltage is reduced to 0.7V or lower:
|
||||
|
||||
|
||||
|
||||
## SMPS (Switched-Mode Power Supply) or DC/DC Converters
|
||||
|
||||
A linear regulator provides the desired output voltage by dissipating
|
||||
excess power as heat in the Zener diode or in the pass
|
||||
transistor. Hence its maximum power efficiency is VOUT/ VIN since the
|
||||
voltage difference is wasted to heat the birds.
|
||||
|
||||
In contrast, a Switched-Mode Power Supply changes output voltage and
|
||||
current by switching non-linear storage elements, such as inductors,
|
||||
transformers and capacitors between different electrical
|
||||
configurations.
|
||||
|
||||
These elements are said to be non-linear because the inductor and
|
||||
transformer respond to changes in current by inducing its own voltage
|
||||
to counter the change in current, whereas a capacitor responds to
|
||||
changes in voltage by inducing its own current to counter the change
|
||||
in voltage.
|
||||
|
||||
Thus, depending on the way the components are arranged, it is possible
|
||||
to obtain SMPS circuits that either have an output voltage higher than
|
||||
the input voltage ("Boost Converters"), or lower than the input
|
||||
voltage ("Buck Converters", as is it subtracts or “Bucks” the supply
|
||||
voltage).
|
||||
|
||||
Because of technology, power inductors are easier to manufacture, take
|
||||
less space and are more stable over time than their counterpart
|
||||
capacitors. This is why most power DC/DC converters are built using
|
||||
inductors. Capacitor-based SMPS are generally used for lower power
|
||||
applications, such as for generating the +12V and -12V voltages
|
||||
required by true RS232 from a +3.3V or +5V power supply in the
|
||||
ubiquitous MAX232 drivers.
|
||||
|
||||
### Boost Converter
|
||||
|
||||
The most basic circuit for the Boost converter is the following:
|
||||
|
||||
|
||||
|
||||
If the switch is driven by a square wave, the peak-to-peak voltage of
|
||||
the waveform measured across the switch can exceed the input voltage
|
||||
from the DC source. This is because the non-linear characteristic of
|
||||
the inductor, and this voltage adds to the source voltage while the
|
||||
switch is open.
|
||||
|
||||
!!! warning
|
||||
In this converter, the output voltage is not isolated from the
|
||||
input voltage.
|
||||
|
||||
### Buck Converter
|
||||
|
||||
The corresponding basic circuit for the Buck converter is the
|
||||
following:
|
||||
|
||||
|
||||
|
||||
The way this converter works is described in details
|
||||
[here][3]. Basically, when the switch is closed, the inductor will
|
||||
produce an opposing voltage across its terminals in response to the
|
||||
changing current, reducing the output voltage, and meanwhile the
|
||||
inductor stores this energy in the form of a magnetic field. When the
|
||||
switch is opened, the current will decrease and will produce a voltage
|
||||
drop across the inductor, and now the inductor becomes a current
|
||||
source, where the stored energy in the inductor's magnetic field is
|
||||
restored and fed to the load.
|
||||
|
||||
!!! warning
|
||||
In this converter too, the output voltage is not isolated from the
|
||||
input voltage.
|
||||
|
||||
### Isolated SMPS
|
||||
|
||||
Isolated Switched-Mode Power Supplies use a transformer to isolate the
|
||||
input voltage from the output voltage, and thus can produce an output
|
||||
of higher or lower voltage than the input by adjusting the turns
|
||||
ratio.
|
||||
|
||||
## Pros and Cons
|
||||
|
||||
Linear regulators are simpler than SMPS, and their linear behavior
|
||||
produce a very clean output voltage, but their efficiency is directly
|
||||
proportional to the difference between the input and output voltage,
|
||||
which is dissipated as heat.
|
||||
|
||||
However, for light loads and/or when the voltage drop-out is low, LDOs
|
||||
are very useful.
|
||||
|
||||
OTOH, SMPS are more complex and require more components, but their
|
||||
efficiency is much better (typically 80-90%), resulting in less heat,
|
||||
with the drawback of a switching electrical noise pollution of both
|
||||
the input voltage (that may couple electrical switching noise back
|
||||
onto the mains power line) and the output voltage (with
|
||||
electromagnetic interference (EMI) and a ripple voltage at the
|
||||
switching frequency and all its harmonic frequencies).
|
||||
|
||||
SMPS are thus almost exclusively used when heavy loads are used and/or
|
||||
when the voltage drop-out is important.
|
||||
|
||||
[1]: https://en.wikipedia.org/wiki/Linear_regulator#Simple_shunt_regulator
|
||||
[2]: https://en.wikipedia.org/wiki/Linear_regulator#Simple_series_regulator
|
||||
[3]: https://en.wikipedia.org/wiki/Buck_converter#Concept
|
||||
|
||||
--8<--
|
||||
includes/glossary.md
|
||||
--8<--
|
||||
143
docs/developer_guide/hardware_reference/screen.md
Normal file
143
docs/developer_guide/hardware_reference/screen.md
Normal file
@@ -0,0 +1,143 @@
|
||||
The second most important part in the **FunKey S** is certainly its
|
||||
screen: in an overall form factor of roughly 45mm x 45mm x 15mm (1.75"
|
||||
x 1.75" x 0.6"), it has to be comfortable enough to provide a good
|
||||
gaming experience.
|
||||
|
||||
In theory, 1.75" would allows to shoehorn a 2.4" (diagonal) square
|
||||
screen, but in practice, 2.4" screens are seldom square and more
|
||||
rectangular in shape.
|
||||
|
||||
Unless you are a large manufacturer and selling millions of devices,
|
||||
you are limited to using the existing screen sizes that are available
|
||||
on the market, which most of the time were designed for a
|
||||
long-forgotten specific devices (think of PDAs, MP3 players,
|
||||
clam-shell phones, pods, etc.) and standard aspect ratio are either
|
||||
1:1, 5:3 or 16:9. Thus, for a given pixel technology, this results in
|
||||
rather standard screen sizes.
|
||||
|
||||
So the next available size down are 2" and 1.8", but these screens
|
||||
tend to be quite thick and based on an older technology, so their
|
||||
typical resolution is rather limited @ 128x160 pixels: too small for
|
||||
gamers.
|
||||
|
||||
Still going down in size, you can find 1.5" to 1.55" screens with an
|
||||
interesting resolution of 240x240 or even 320 x 320 ("Retina") pixels,
|
||||
but most of them use a fast MIPI DSi interface. These particular
|
||||
screens were popular as they were used in the 6th-generation "square"
|
||||
iPods, but unfortunately, they require a dedicated controller on the
|
||||
host side, which is only available in higher-end SoC.
|
||||
|
||||
Another important characteristic of the required screen is that it
|
||||
needs to have a narrow flex cable in order to be rolled into the hinge
|
||||
(like a _fly-paper_) in order to spread the mechanical flex constraint
|
||||
over several loop rather than at always the same section, resulting in
|
||||
less wear and an expected longer lifespan.
|
||||
|
||||
Fortunately, we found this 1.54" LCD screen on AliBaba:
|
||||
|
||||
|
||||
|
||||
What makes this screen special is its standard SPI interface, which
|
||||
only requires a few wires and thus a narrow flex cable like the MIPI
|
||||
DSi interface, so it is easy to roll into a hinge. But unlike the MIPI
|
||||
DSi one, the SPI interface is readily available on most of the SoC,
|
||||
including the Allwinner V3s.
|
||||
|
||||
This 1.54" display features a 240x240 16/18-bit full color pixel
|
||||
resolution and is an **IPS** display, so the color looks great up to
|
||||
80 degrees off-axis in any direction.
|
||||
|
||||
However, in order to achieve a 50 fps @ 240 x 240 pixel resolution in
|
||||
RGB565 (2 bytes / pixel), this requires a ~44 MHz SPI clock rate,
|
||||
which is rather high.
|
||||
|
||||
Once again, we were fortunate as both the V3s CPU and the screen
|
||||
built-in controller (a Sitronix [ST7789V][1]) both support this high
|
||||
clock speed (after checking with the manufacturer and despite the
|
||||
controller datasheet that specifies only a serial clock cycle (Write)
|
||||
of 66 ns or 15 MHz!).
|
||||
|
||||
We were even luckier as its backlight consists in 3 white LEDs in
|
||||
parallel and not in series, such that no additional step-up DC-DC
|
||||
converter is required, as a standard 3.3V / 60 mA (typical) power
|
||||
supply is sufficient. Of course, we won't be able to drive this
|
||||
current directly from a CPU GPIO and the backlight will require an
|
||||
additional transistor to interface to the LCD backlight.
|
||||
|
||||
Its flex cable requires a mating Hirose 0.4 mm pitch
|
||||
[DF37NB-24DS-0.4V][2] dual row SMT connector, out of which only one
|
||||
single row is actually used.
|
||||
|
||||
## Customization
|
||||
|
||||
Unfortunately, the flex cable for the stock LCD screen we found does
|
||||
not match our particular **FunKey S** mechanical design.
|
||||
|
||||
For the prototypes, we designed custom flex extension cables for a ~
|
||||
$100 cost, but we had to design [our own custom flex][3] and have this
|
||||
standard screen assembly attached to it for mass production, with a
|
||||
one-time tooling fee of ~ $800.
|
||||
|
||||
## Schematic
|
||||
|
||||
The schematic is quite simple:
|
||||
|
||||
{.lightbox}
|
||||
|
||||
The main component is of course the Hirose screen connector **J3**,
|
||||
with the following signals:
|
||||
|
||||
- LEDA: the backlight LED common Anode connection (+)
|
||||
- GND
|
||||
- +3V3 power supply
|
||||
- /SPI_CS: SPI Chip Select
|
||||
- SPI_MOSI: SPI Master Out / Slave In
|
||||
- SPI_CLK: SPI Clock
|
||||
- TE: Tearing Effect sync signal from the screen
|
||||
- RS: LCD-specific Register/Memory Select (or Data/Control Select)
|
||||
- LCD_RESET: LCD Reset
|
||||
|
||||
All data signals feature an ESD TVS protection diode **D19-D24** and
|
||||
**D37**, and except for the power supplies and LEDA + LCD_RESET and TE
|
||||
signals, all signals are directly connected to the V3s CPU's SPI
|
||||
interface, so there is not much to say about these.
|
||||
|
||||
The LCD_RESET signal is controlled by a V3s GPIO (PB2 on pin 41).
|
||||
|
||||
The TE signal from the screen controller is fed to an
|
||||
interrupt-enabled input pin PB1 (pin 40) in order to synchronize the
|
||||
sending of data to the screen with its inactive period in order to
|
||||
avoid the hardware tearing effect.
|
||||
|
||||
## Backlight PWM
|
||||
|
||||
The backlight control requires a few more components: a MOSFET-P
|
||||
transistor **Q1** and 2 resistors **R5** and **R7** to provide its
|
||||
polarization, more on this below.
|
||||
|
||||
As the backlight LEDs cathode (-) pin are directly tied to GND within
|
||||
the screen, we need to drive these LEDs "from the high-side",
|
||||
i.e. between the +3V3 power supply and the LEDA pin, so a MOSFET-P
|
||||
transistor is necessary:
|
||||
|
||||
{.lightbox}
|
||||
|
||||
As we want the backlight to be on by default, we need to drive it to
|
||||
GND by default: this is the role of **R7**. The role of **R5** is then
|
||||
to make sure that -Vgs is driven below its threshold voltage and turns
|
||||
off the transistor when the CPU drives a GPIO high.
|
||||
|
||||
As an ultimate sophistication, we can drive the backlight from the CPU
|
||||
using one of its built-in PWM controllers PWM0 with a varying
|
||||
duty-cycle, thus controlling the LCD backlight brightness
|
||||
accurately. For this purpose, the other end of the **R5** resistor is
|
||||
connected to the PB4 output (pin 43) on the V3s, wich provides this
|
||||
function.
|
||||
|
||||
[1]: https://www.numworks.com/shared/binary/datasheets/st7789v-lcd-controller-73f8bc3e.pdf
|
||||
[2]: https://github.com/FunKey-Project/FunKey-S-Hardware/blob/master/Datasheets/1811071030_HRS-Hirose-DF37NC-24DS-0-4V-51_C324720.pdf
|
||||
[3]: https://github.com/FunKey-Project/FunKey-S-Hardware/blob/master/Datasheets/DISPLAY%20-%20SF-TC154B-8737A-N%20-%20CUSTOM%20FLEX%20-%200.3.PDF
|
||||
|
||||
--8<--
|
||||
includes/glossary.md
|
||||
--8<--
|
||||
125
docs/developer_guide/hardware_reference/sd-card.md
Normal file
125
docs/developer_guide/hardware_reference/sd-card.md
Normal file
@@ -0,0 +1,125 @@
|
||||
The **FunKey S** game console uses the SD Card both as its boot device
|
||||
and its only storage device, so a good operation of this interface is
|
||||
absolutely mandatory.
|
||||
|
||||
The Allwinner V3s provides 2x 4-bit MMC / SD Card / SDIO
|
||||
interfaces. In the FunKey, only interface #0 is used.
|
||||
|
||||
If you look on the Web, you will find many contradictory SD Card
|
||||
interface designs, with a combination of pull-up / pull-down
|
||||
resistors, ESD devices and power supply filtering, with all pins wired
|
||||
or not, such that it is very difficult to know what is really
|
||||
required. To better understand the situation, we need to go back to
|
||||
the specifications.
|
||||
|
||||
## Specifications
|
||||
|
||||
The SD Card physical interface is provided in the "<i>SD
|
||||
specifications, part 1, Physical Layer Specification version 2.00, May
|
||||
9, 2006</i>", for which a simplified version is available [here][1].
|
||||
|
||||
The MMC phyiscal interface can be found in the "<i>Multi Media Card
|
||||
System Specification version 4.3, JESD84-A43, November 2007</i>",
|
||||
available [here][2] (registration required).
|
||||
|
||||
But a good summary of the requirements is given in the "_[AN10911
|
||||
SD(HC)-memory card and MMC Interface conditioning][3]_" application
|
||||
note from NXP, from which this schematic is taken:
|
||||
|
||||
{.lightbox}
|
||||
|
||||
!!! Warning
|
||||
This schematic does not include details concerning card-supply and
|
||||
typical power-supply decoupling capacitors.
|
||||
|
||||
## Write Protect (WP)
|
||||
|
||||
A mechanical write protect switch is provided in the full-size SD
|
||||
Card, but not in the mini or micro SD Card form factor. As we plan to
|
||||
use a micro SD Card only, it is not used for the FunKey, along with
|
||||
its pull-up resistor and ESD protection.
|
||||
|
||||
## Card Detection (CD)
|
||||
|
||||
As the SD Card is mandatory to boot the **FunKey S**, is always
|
||||
inserted and opening the device is required for its removal, we don't
|
||||
need the optional card detect mechanical switch feature (even if the
|
||||
chosen connector provides it) and its related pull-up resistor and ESD
|
||||
protection.
|
||||
|
||||
The SD Card specification provides another mean to detect the card
|
||||
using a card built-in pull-up resistor on its DAT3 signal, that can be
|
||||
later disconnected during normal operation using he
|
||||
**SET_CLR_CARD_DETECT** (**ACMD42**) command. In order to correctly
|
||||
detect if the card is inserted, a high value external pull-down
|
||||
resistor (> 270 kΩ) is required to drive the detect signal low when no
|
||||
card is inserted, while the card built-in 10-50 kΩ resistor will drive
|
||||
this signal high when inserted.
|
||||
|
||||
However, this feature is not compatible with MMC cards, so its usage
|
||||
should be avoided and the mechanical detection is preferred.
|
||||
|
||||
## Pull-Up Resistors
|
||||
|
||||
Both the SD Card and MMC specifications require not to leave the
|
||||
interface signals floating, except for the CLK signal, where a pull
|
||||
resistor would cause significant signal distortion because of the
|
||||
required high speed and short rise/fall times. However, it is
|
||||
recommended to add a series resistor on this CLK signal as close as
|
||||
possible to the clock source (the CPU) to avoid ringing, as we already
|
||||
discussed it in the page about the [CPU][4].
|
||||
|
||||
Fortunately, the Allwinner V3s CPU provides internal pull-up resistors
|
||||
for all these signals, so we don't have to add external pull-up
|
||||
resistors. These resistors are given with a typical value of 100 kΩ
|
||||
(50 min, 150 max). Unfortunately, the CMD signal for MMC card features
|
||||
an open-drain output mode, and its value should be undercut (down to
|
||||
4.7 kΩ) to guarantee a sufficiently short rise time in this mode.
|
||||
|
||||
## Schematics
|
||||
|
||||
The FunKey SD Card interface schematic is the following:
|
||||
|
||||
{.lightbox}
|
||||
|
||||
{: align=left }
|
||||
|
||||
As can be expected, the main component is the [Micro SD (TF Card)
|
||||
Push/Pull connector][5] **J4**, which has been selected for its
|
||||
low-profile (1.3 mm height) characteristic and overall minimal
|
||||
dimensions.
|
||||
|
||||
!!! Tip
|
||||
|
||||
"Push-Pull" means that you have to "Push" to insert the card and
|
||||
to "Pull" to remove it, i.e. the operation is completely manual,
|
||||
whereas "Push/Push" implies that you have a bistable mechanism to
|
||||
remove the card.
|
||||
|
||||
Even if in the FunKey device the SD Card and its connector are not
|
||||
accessible without opening the enclosure, there may be some situations
|
||||
where the user may decide to do so. We thus attach an ESD protection
|
||||
TVS diode (**D16**, **D17**, **D18**, **D25**, **D26**, **D27**,
|
||||
**D28**) on each signal to avoid any ESD hazard.
|
||||
|
||||
As discussed above, a single pull-up resistor **R10** is used on the CMD
|
||||
signal for MMC compatibility.
|
||||
|
||||
The micro SD Card connector built-in card detection switch is not
|
||||
used, since the card must always be inserted for the **FunKey S** to
|
||||
boot, and the corresponding pins are thus connected to GND.
|
||||
|
||||
The SD Card power supply is applied through an RC low-pass filter
|
||||
**R9** / **C11** in order to provide a soft-start operation, as the
|
||||
card built-in large bulk capacitor on its power rail may collapse the
|
||||
supply voltage when initially powered up.
|
||||
|
||||
[1]: https://www.sdcard.org/downloads/pls/click.php?p=Part1_Physical_Layer_Simplified_Specification_Ver6.00.jpg&f=Part1_Physical_Layer_Simplified_Specification_Ver6.00.pdf&e=EN_SS1
|
||||
[2]: https://www.jedec.org/document_search/field_keywords/emmc-3147
|
||||
[3]: https://www.mouser.com/catalog/specsheets/an10911.pdf
|
||||
[4]: /developers/hardware/cpu
|
||||
[5]: https://github.com/FunKey-Project/FunKey-S-Hardware/blob/master/Datasheets/C266613_%E6%8A%BD%E6%8B%89%E5%BC%8FTF%E5%8D%A1%E5%BA%A7_2018-08-20.PDF
|
||||
|
||||
--8<--
|
||||
includes/glossary.md
|
||||
--8<--
|
||||
50
docs/developer_guide/hardware_reference/uart.md
Normal file
50
docs/developer_guide/hardware_reference/uart.md
Normal file
@@ -0,0 +1,50 @@
|
||||
The Allwinner V3s provides 3x UARTs (Universal Asynchronous Receivers
|
||||
/ Transmitters): UART0 with only RX and TX signals, and UART1 and
|
||||
UART2 with additional RTS and CTS hardware flow control signals.
|
||||
|
||||
Like most SoCs, the Allwinner V3s provides a serial console as a
|
||||
control terminal for debug and/or normal operation. By default, it is
|
||||
mapped to UART0, and it is used by the BROM (Boot Rom), the U-Boot
|
||||
bootloader and by the Linux kernel to output messages during the boot
|
||||
process, and later by the Linux kernel to log messages during normal
|
||||
operation. Depending on the configuration, it can be used too for
|
||||
loging into the system over an UART.
|
||||
|
||||
The Console schematic only requires a minimum of external components:
|
||||
|
||||
{.lightbox}
|
||||
|
||||
Besides the 3-pin 1.27 mm (0.05") pitch header J1 that will not be
|
||||
mounted on standard products, there is only a single series resistor
|
||||
**R3**.
|
||||
|
||||
What is the purpose of this resistor?
|
||||
|
||||
- As explained previously for the SD Card clock signal, this may be
|
||||
to prevent ringing. But given the relatively slow signal speed
|
||||
(115200 bps), it is not the case here
|
||||
|
||||
- If it were placed on the RX input signal, this could prevent frying
|
||||
the input pin if a large voltage (+5V, for example) is applied to
|
||||
it by dissipating the excessive voltage as heat in the resistor. It
|
||||
is not the case here, as the resistor is placed on the TX output
|
||||
signal, but we could have added one, if only we had some space left
|
||||
on the board... But as the V3s SoC can tolerate input voltages up
|
||||
to +3.6V on its pins, we should be safe!
|
||||
|
||||
- In fact, the resistor is on the output TX signal to prevent
|
||||
short-circuits if the serial cable is reversed and the 2 TX outputs
|
||||
are connected together, one driving the signal low, while the other
|
||||
is driving it high: again in this case, the voltage difference
|
||||
between the 2 outputs will be burned as heat in the resistor,
|
||||
saving the internal output buffers!
|
||||
|
||||
!!! Warning
|
||||
|
||||
There is no ESD protection TVS diodes on the UART: this interface
|
||||
is not supposed to be mounted in the final user device, and PCB
|
||||
space is really constrained in this area, so they are omitted.
|
||||
|
||||
--8<--
|
||||
includes/glossary.md
|
||||
--8<--
|
||||
55
docs/developer_guide/hardware_reference/usb.md
Normal file
55
docs/developer_guide/hardware_reference/usb.md
Normal file
@@ -0,0 +1,55 @@
|
||||
In the **FunKey S** device, the USB interface has 2 functions:
|
||||
|
||||
- provide an external power supply source for both powering the
|
||||
device and charging the built-in LiPo battery
|
||||
- provide a data interface to transfer firmware upgrades,
|
||||
configuration files, game emulators and game ROMs
|
||||
|
||||
The first function only requires the +5V USB power and GND pins. The
|
||||
second function requires to wire the additional differential data
|
||||
lines D+ and D-. As we only need to operate as an USB device and
|
||||
although the V3s is able to work as either an USB host or USB device
|
||||
using the USB OTG protocol, we don't need the ID pin to determine by
|
||||
the cable wiring which role we must take.
|
||||
|
||||
{: align=left }
|
||||
|
||||
The main part is of course the [Micro USB edge-mounted connector][1]
|
||||
**J2**, which we chose in order to "mask out" its already low-profile
|
||||
height into the PCB thickness. And with its "harpoon-like"
|
||||
through-hole legs, it should avoid tearing it off the board if the
|
||||
user don't pull the chord straight.
|
||||
|
||||
The USB schematic is the following:
|
||||
|
||||
{.lightbox}
|
||||
|
||||
Before connecting 2 devices using an USB cable, they may be at
|
||||
completely different absolute voltages, and during cable insertion,
|
||||
the shield will be in contact before the other pins, including
|
||||
GND. The **C6** capacitor between the Protective Earth (Shield) and
|
||||
GND is here to provide an AC path for sinking this difference in
|
||||
voltage and align the GND levels when plugin the cable.
|
||||
|
||||
The resistor **R4** on the USB ID connector pin should probably not be
|
||||
mounted: as we act only as an USB device, this pin should be left
|
||||
floating.
|
||||
|
||||
The capacitors **C7**, **C8**, **C10** and ferrite bead **L2** form a
|
||||
constant-k 3 pole CLC low pass filter to remove any spurious in/out on
|
||||
the USB power supply wire. The USB 2.0 specification limits the
|
||||
maximum bulk capacitance value to 10 µF in order to avoid power supply
|
||||
excessive droops when plugin in a device with a discharged large bulk
|
||||
capacitor.
|
||||
|
||||
**D15** is a [NXP PRTR5V0U2X,215][2] combined TVS protection diode for
|
||||
the VBUS pin and a set of clamping diodes that will limit the voltage
|
||||
on D+ and D- pins to stay between GND and VBUS levels to in order to
|
||||
protect the V3s USB driver from under / over-voltages.
|
||||
|
||||
[1]: https://github.com/FunKey-Project/FunKey-S-Hardware/blob/master/Datasheets/C40958_MICRO5P%E6%B2%89%E6%9D%BF%E5%BC%8F0.8%E5%9B%9B%E8%84%9A%E5%85%A8%E6%8F%92%E6%97%A0%E5%AF%BC%E4%BD%8D%E6%9C%89%E5%AD%94%E8%80%90%E9%AB%98%E6%B8%A9_2016-05-20.PDF
|
||||
[2]: https://github.com/FunKey-Project/FunKey-S-Hardware/blob/master/Datasheets/C12333_PRTR5V0U2X%2C215_2017-10-31.PDF
|
||||
|
||||
--8<--
|
||||
includes/glossary.md
|
||||
--8<--
|
||||
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|
||||
|
||||
--8<--
|
||||
includes/glossary.md
|
||||
--8<--
|
||||
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|
||||
|
||||
--8<--
|
||||
includes/glossary.md
|
||||
--8<--
|
||||
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|
||||
|
||||
--8<--
|
||||
includes/glossary.md
|
||||
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|
||||
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|
||||
|
||||
--8<--
|
||||
includes/glossary.md
|
||||
--8<--
|
||||
@@ -0,0 +1,4 @@
|
||||
|
||||
--8<--
|
||||
includes/glossary.md
|
||||
--8<--
|
||||
57
docs/developer_guide/software_reference/index.md
Normal file
57
docs/developer_guide/software_reference/index.md
Normal file
@@ -0,0 +1,57 @@
|
||||
The **FunKey S** retro-gaming console software contains a set of
|
||||
console emulators, standalone games, applications and utilities using
|
||||
a custom Operating System (OS) that from now on will be referenced as
|
||||
**_FunKey-OS_**.
|
||||
|
||||
The **FunKey-OS** is a Linux-based operating system, optimized for the
|
||||
**FunKey-S** hardware, with a special focus on performance and fast
|
||||
boot time.
|
||||
|
||||
## Instant Action
|
||||
|
||||
The **FunKey S** introduces a unique feature called **_Instant
|
||||
Action_**, which enables automatically saving the running state when
|
||||
closing the console before turning it off, and restoring this state
|
||||
when opening and turning it back on in a matter of seconds.
|
||||
|
||||
This feature is only possible because of the optimized fast boot time
|
||||
detailed in the [Boot Process][1] section.
|
||||
|
||||
## Storage
|
||||
|
||||
The only storage system available in the **FunKey S** is its
|
||||
integrated MicroSD card. Most of its contents is made available to a
|
||||
host computer when connected over USB.
|
||||
|
||||
The MicroSD card format is detailed in the [Disk Partition][2]
|
||||
section.
|
||||
|
||||
## Video Processing
|
||||
|
||||
The **FunKey-S** CPU does not feature a GPU. For this reason, the
|
||||
**FunKey-S** cannot use a hardware-accelerated OpenGL engine, and
|
||||
adding a software-emulated OpenGL-ES engine is not efficient, given
|
||||
the limited CPU performance.
|
||||
|
||||
However, because of the small screen size and the fact that all
|
||||
applications are used in full-screen mode only, there is no need for a
|
||||
full-blown windowing system like X11, which greatly simplifies the
|
||||
video processing as no window overlapping or frame decoration is thus
|
||||
required.
|
||||
|
||||
Instead, all graphical computations are performed by the CPU itself,
|
||||
directly into the video frame buffer that will be sent to the screen
|
||||
for display.
|
||||
|
||||
## User Input
|
||||
|
||||
The **FunKey S** has no standard keyboard but features common
|
||||
console-oriented controls in the form of a D-Pad, A/B/X/Y Pad,
|
||||
Menu/On/Off, Fn and Start buttons.
|
||||
|
||||
[1]: boot_process/index.md
|
||||
[2]: sd_card_layout/partition_map.md
|
||||
|
||||
--8<--
|
||||
includes/glossary.md
|
||||
--8<--
|
||||
4
docs/developer_guide/software_reference/input_mapping.md
Normal file
4
docs/developer_guide/software_reference/input_mapping.md
Normal file
@@ -0,0 +1,4 @@
|
||||
|
||||
--8<--
|
||||
includes/glossary.md
|
||||
--8<--
|
||||
@@ -0,0 +1,4 @@
|
||||
|
||||
--8<--
|
||||
includes/glossary.md
|
||||
--8<--
|
||||
@@ -0,0 +1,4 @@
|
||||
|
||||
--8<--
|
||||
includes/glossary.md
|
||||
--8<--
|
||||
@@ -0,0 +1,4 @@
|
||||
|
||||
--8<--
|
||||
includes/glossary.md
|
||||
--8<--
|
||||
@@ -0,0 +1,4 @@
|
||||
|
||||
--8<--
|
||||
includes/glossary.md
|
||||
--8<--
|
||||
@@ -0,0 +1,4 @@
|
||||
|
||||
--8<--
|
||||
includes/glossary.md
|
||||
--8<--
|
||||
@@ -0,0 +1,4 @@
|
||||
|
||||
--8<--
|
||||
includes/glossary.md
|
||||
--8<--
|
||||
4
docs/developer_guide/tutorials/access_recovery.md
Normal file
4
docs/developer_guide/tutorials/access_recovery.md
Normal file
@@ -0,0 +1,4 @@
|
||||
|
||||
--8<--
|
||||
includes/glossary.md
|
||||
--8<--
|
||||
@@ -0,0 +1,4 @@
|
||||
|
||||
--8<--
|
||||
includes/glossary.md
|
||||
--8<--
|
||||
@@ -0,0 +1,4 @@
|
||||
|
||||
--8<--
|
||||
includes/glossary.md
|
||||
--8<--
|
||||
@@ -0,0 +1,4 @@
|
||||
|
||||
--8<--
|
||||
includes/glossary.md
|
||||
--8<--
|
||||
@@ -0,0 +1,4 @@
|
||||
|
||||
--8<--
|
||||
includes/glossary.md
|
||||
--8<--
|
||||
4
docs/developer_guide/tutorials/build_system/index.md
Normal file
4
docs/developer_guide/tutorials/build_system/index.md
Normal file
@@ -0,0 +1,4 @@
|
||||
|
||||
--8<--
|
||||
includes/glossary.md
|
||||
--8<--
|
||||
4
docs/developer_guide/tutorials/ssh_connection.md
Normal file
4
docs/developer_guide/tutorials/ssh_connection.md
Normal file
@@ -0,0 +1,4 @@
|
||||
|
||||
--8<--
|
||||
includes/glossary.md
|
||||
--8<--
|
||||
4
docs/developer_guide/tutorials/uart_connection.md
Normal file
4
docs/developer_guide/tutorials/uart_connection.md
Normal file
@@ -0,0 +1,4 @@
|
||||
|
||||
--8<--
|
||||
includes/glossary.md
|
||||
--8<--
|
||||
Reference in New Issue
Block a user