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Creation of Cybook 2416 (actually Gen4) repository

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This file describes the configuration and behavior of KGDB for the SH
kernel. Based on a description from Henry Bell <henry.bell@st.com>, it
has been modified to account for quirks in the current implementation.
Version
=======
This version of KGDB was written for 2.4.xx kernels for the SH architecture.
Further documentation is available from the linux-sh project website.
Debugging Setup: Host
======================
The two machines will be connected together via a serial line - this
should be a null modem cable i.e. with a twist.
On your DEVELOPMENT machine, go to your kernel source directory and
build the kernel, enabling KGDB support in the "kernel hacking" section.
This includes the KGDB code, and also makes the kernel be compiled with
the "-g" option set -- necessary for debugging.
To install this new kernel, use the following installation procedure.
Decide on which tty port you want the machines to communicate, then
cable them up back-to-back using the null modem. On the DEVELOPMENT
machine, you may wish to create an initialization file called .gdbinit
(in the kernel source directory or in your home directory) to execute
commonly-used commands at startup.
A minimal .gdbinit might look like this:
file vmlinux
set remotebaud 115200
target remote /dev/ttyS0
Change the "target" definition so that it specifies the tty port that
you intend to use. Change the "remotebaud" definition to match the
data rate that you are going to use for the com line (115200 is the
default).
Debugging Setup: Target
========================
By default, the KGDB stub will communicate with the host GDB using
ttySC1 at 115200 baud, 8 databits, no parity; these defaults can be
changed in the kernel configuration. As the kernel starts up, KGDB will
initialize so that breakpoints, kernel segfaults, and so forth will
generally enter the debugger.
This behavior can be modified by including the "kgdb" option in the
kernel command line; this option has the general form:
kgdb=<ttyspec>,<action>
The <ttyspec> indicates the port to use, and can optionally specify
baud, parity and databits -- e.g. "ttySC0,9600N8" or "ttySC1,19200".
The <action> can be "halt" or "disabled". The "halt" action enters the
debugger via a breakpoint as soon as kgdb is initialized; the "disabled"
action causes kgdb to ignore kernel segfaults and such until explicitly
entered by a breakpoint in the code or by external action (sysrq or NMI).
(Both <ttyspec> and <action> can appear alone, w/o the separating comma.)
For example, if you wish to debug early in kernel startup code, you
might specify the halt option:
kgdb=halt
Boot the TARGET machine, which will appear to hang.
On your DEVELOPMENT machine, cd to the source directory and run the gdb
program. (This is likely to be a cross GDB which runs on your host but
is built for an SH target.) If everything is working correctly you
should see gdb print out a few lines indicating that a breakpoint has
been taken. It will actually show a line of code in the target kernel
inside the gdbstub activation code.
NOTE: BE SURE TO TERMINATE OR SUSPEND any other host application which
may be using the same serial port (for example, a terminal emulator you
have been using to connect to the target boot code.) Otherwise, data
from the target may not all get to GDB!
You can now use whatever gdb commands you like to set breakpoints.
Enter "continue" to start your target machine executing again. At this
point the target system will run at full speed until it encounters
your breakpoint or gets a segment violation in the kernel, or whatever.
Serial Ports: KGDB, Console
============================
This version of KGDB may not gracefully handle conflict with other
drivers in the kernel using the same port. If KGDB is configured on the
same port (and with the same parameters) as the kernel console, or if
CONFIG_SH_KGDB_CONSOLE is configured, things should be fine (though in
some cases console messages may appear twice through GDB). But if the
KGDB port is not the kernel console and used by another serial driver
which assumes different serial parameters (e.g. baud rate) KGDB may not
recover.
Also, when KGDB is entered via sysrq-g (requires CONFIG_KGDB_SYSRQ) and
the kgdb port uses the same port as the console, detaching GDB will not
restore the console to working order without the port being re-opened.
Another serious consequence of this is that GDB currently CANNOT break
into KGDB externally (e.g. via ^C or <BREAK>); unless a breakpoint or
error is encountered, the only way to enter KGDB after the initial halt
(see above) is via NMI (CONFIG_KGDB_NMI) or sysrq-g (CONFIG_KGDB_SYSRQ).
Code is included for the basic Hitachi Solution Engine boards to allow
the use of ttyS0 for KGDB if desired; this is less robust, but may be
useful in some cases. (This cannot be selected using the config file,
but only through the kernel command line, e.g. "kgdb=ttyS0", though the
configured defaults for baud rate etc. still apply if not overridden.)
If gdbstub Does Not Work
========================
If it doesn't work, you will have to troubleshoot it. Do the easy
things first like double checking your cabling and data rates. You
might try some non-kernel based programs to see if the back-to-back
connection works properly. Just something simple like cat /etc/hosts
/dev/ttyS0 on one machine and cat /dev/ttyS0 on the other will tell you
if you can send data from one machine to the other. There is no point
in tearing out your hair in the kernel if the line doesn't work.
If you need to debug the GDB/KGDB communication itself, the gdb commands
"set debug remote 1" and "set debug serial 1" may be useful, but be
warned: they produce a lot of output.
Threads
=======
Each process in a target machine is seen as a gdb thread. gdb thread related
commands (info threads, thread n) can be used. CONFIG_KGDB_THREAD must
be defined for this to work.
In this version, kgdb reports PID_MAX (32768) as the process ID for the
idle process (pid 0), since GDB does not accept 0 as an ID.
Detaching (exiting KGDB)
=========================
There are two ways to resume full-speed target execution: "continue" and
"detach". With "continue", GDB inserts any specified breakpoints in the
target code and resumes execution; the target is still in "gdb mode".
If a breakpoint or other debug event (e.g. NMI) happens, the target
halts and communicates with GDB again, which is waiting for it.
With "detach", GDB does *not* insert any breakpoints; target execution
is resumed and GDB stops communicating (does not wait for the target).
In this case, the target is no longer in "gdb mode" -- for example,
console messages no longer get sent separately to the KGDB port, or
encapsulated for GDB. If a debug event (e.g. NMI) occurs, the target
will re-enter "gdb mode" and will display this fact on the console; you
must give a new "target remote" command to gdb.
NOTE: TO AVOID LOSSING CONSOLE MESSAGES IN CASE THE KERNEL CONSOLE AND
KGDB USING THE SAME PORT, THE TARGET WAITS FOR ANY INPUT CHARACTER ON
THE KGDB PORT AFTER A DETACH COMMAND. For example, after the detach you
could start a terminal emulator on the same host port and enter a <cr>;
however, this program must then be terminated or suspended in order to
use GBD again if KGDB is re-entered.
Acknowledgements
================
This code was mostly generated by Henry Bell <henry.bell@st.com>;
largely from KGDB by Amit S. Kale <akale@veritas.com> - extracts from
code by Glenn Engel, Jim Kingdon, David Grothe <dave@gcom.com>, Tigran
Aivazian <tigran@sco.com>, William Gatliff <bgat@open-widgets.com>, Ben
Lee, Steve Chamberlain and Benoit Miller <fulg@iname.com> are also
included.
Jeremy Siegel
<jsiegel@mvista.com>

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Adding a new board to LinuxSH
================================
Paul Mundt <lethal@linux-sh.org>
This document attempts to outline what steps are necessary to add support
for new boards to the LinuxSH port under the new 2.5 and 2.6 kernels. This
also attempts to outline some of the noticeable changes between the 2.4
and the 2.5/2.6 SH backend.
1. New Directory Structure
==========================
The first thing to note is the new directory structure. Under 2.4, most
of the board-specific code (with the exception of stboards) ended up
in arch/sh/kernel/ directly, with board-specific headers ending up in
include/asm-sh/. For the new kernel, things are broken out by board type,
companion chip type, and CPU type. Looking at a tree view of this directory
hierarchy looks like the following:
Board-specific code:
.
|-- arch
| `-- sh
| `-- boards
| |-- adx
| | `-- board-specific files
| |-- bigsur
| | `-- board-specific files
| |
| ... more boards here ...
|
`-- include
`-- asm-sh
|-- adx
| `-- board-specific headers
|-- bigsur
| `-- board-specific headers
|
.. more boards here ...
Next, for companion chips:
.
`-- arch
`-- sh
`-- cchips
`-- hd6446x
|-- hd64461
| `-- cchip-specific files
`-- hd64465
`-- cchip-specific files
... and so on. Headers for the companion chips are treated the same way as
board-specific headers. Thus, include/asm-sh/hd64461 is home to all of the
hd64461-specific headers.
Finally, CPU family support is also abstracted:
.
|-- arch
| `-- sh
| |-- kernel
| | `-- cpu
| | |-- sh2
| | | `-- SH-2 generic files
| | |-- sh3
| | | `-- SH-3 generic files
| | `-- sh4
| | `-- SH-4 generic files
| `-- mm
| `-- This is also broken out per CPU family, so each family can
| have their own set of cache/tlb functions.
|
`-- include
`-- asm-sh
|-- cpu-sh2
| `-- SH-2 specific headers
|-- cpu-sh3
| `-- SH-3 specific headers
`-- cpu-sh4
`-- SH-4 specific headers
It should be noted that CPU subtypes are _not_ abstracted. Thus, these still
need to be dealt with by the CPU family specific code.
2. Adding a New Board
=====================
The first thing to determine is whether the board you are adding will be
isolated, or whether it will be part of a family of boards that can mostly
share the same board-specific code with minor differences.
In the first case, this is just a matter of making a directory for your
board in arch/sh/boards/ and adding rules to hook your board in with the
build system (more on this in the next section). However, for board families
it makes more sense to have a common top-level arch/sh/boards/ directory
and then populate that with sub-directories for each member of the family.
Both the Solution Engine and the hp6xx boards are an example of this.
After you have setup your new arch/sh/boards/ directory, remember that you
should also add a directory in include/asm-sh for headers localized to this
board (if there are going to be more than one). In order to interoperate
seamlessly with the build system, it's best to have this directory the same
as the arch/sh/boards/ directory name, though if your board is again part of
a family, the build system has ways of dealing with this (via incdir-y
overloading), and you can feel free to name the directory after the family
member itself.
There are a few things that each board is required to have, both in the
arch/sh/boards and the include/asm-sh/ hierarchy. In order to better
explain this, we use some examples for adding an imaginary board. For
setup code, we're required at the very least to provide definitions for
get_system_type() and platform_setup(). For our imaginary board, this
might look something like:
/*
* arch/sh/boards/vapor/setup.c - Setup code for imaginary board
*/
#include <linux/init.h>
#include <asm/rtc.h> /* for board_time_init() */
const char *get_system_type(void)
{
return "FooTech Vaporboard";
}
int __init platform_setup(void)
{
/*
* If our hardware actually existed, we would do real
* setup here. Though it's also sane to leave this empty
* if there's no real init work that has to be done for
* this board.
*/
/*
* Presume all FooTech boards have the same broken timer,
* and also presume that we've defined foo_timer_init to
* do something useful.
*/
board_time_init = foo_timer_init;
/* Start-up imaginary PCI ... */
/* And whatever else ... */
return 0;
}
Our new imaginary board will also have to tie into the machvec in order for it
to be of any use.
machvec functions fall into a number of categories:
- I/O functions to IO memory (inb etc) and PCI/main memory (readb etc).
- I/O mapping functions (ioport_map, ioport_unmap, etc).
- a 'heartbeat' function.
- PCI and IRQ initialization routines.
- Consistent allocators (for boards that need special allocators,
particularly for allocating out of some board-specific SRAM for DMA
handles).
There are machvec functions added and removed over time, so always be sure to
consult include/asm-sh/machvec.h for the current state of the machvec.
The kernel will automatically wrap in generic routines for undefined function
pointers in the machvec at boot time, as machvec functions are referenced
unconditionally throughout most of the tree. Some boards have incredibly
sparse machvecs (such as the dreamcast and sh03), whereas others must define
virtually everything (rts7751r2d).
Adding a new machine is relatively trivial (using vapor as an example):
If the board-specific definitions are quite minimalistic, as is the case for
the vast majority of boards, simply having a single board-specific header is
sufficient.
- add a new file include/asm-sh/vapor.h which contains prototypes for
any machine specific IO functions prefixed with the machine name, for
example vapor_inb. These will be needed when filling out the machine
vector.
Note that these prototypes are generated automatically by setting
__IO_PREFIX to something sensible. A typical example would be:
#define __IO_PREFIX vapor
#include <asm/io_generic.h>
somewhere in the board-specific header. Any boards being ported that still
have a legacy io.h should remove it entirely and switch to the new model.
- Add machine vector definitions to the board's setup.c. At a bare minimum,
this must be defined as something like:
struct sh_machine_vector mv_vapor __initmv = {
.mv_name = "vapor",
};
ALIAS_MV(vapor)
- finally add a file arch/sh/boards/vapor/io.c, which contains definitions of
the machine specific io functions (if there are enough to warrant it).
3. Hooking into the Build System
================================
Now that we have the corresponding directories setup, and all of the
board-specific code is in place, it's time to look at how to get the
whole mess to fit into the build system.
Large portions of the build system are now entirely dynamic, and merely
require the proper entry here and there in order to get things done.
The first thing to do is to add an entry to arch/sh/Kconfig, under the
"System type" menu:
config SH_VAPOR
bool "Vapor"
help
select Vapor if configuring for a FooTech Vaporboard.
next, this has to be added into arch/sh/Makefile. All boards require a
machdir-y entry in order to be built. This entry needs to be the name of
the board directory as it appears in arch/sh/boards, even if it is in a
sub-directory (in which case, all parent directories below arch/sh/boards/
need to be listed). For our new board, this entry can look like:
machdir-$(CONFIG_SH_VAPOR) += vapor
provided that we've placed everything in the arch/sh/boards/vapor/ directory.
Next, the build system assumes that your include/asm-sh directory will also
be named the same. If this is not the case (as is the case with multiple
boards belonging to a common family), then the directory name needs to be
implicitly appended to incdir-y. The existing code manages this for the
Solution Engine and hp6xx boards, so see these for an example.
Once that is taken care of, it's time to add an entry for the mach type.
This is done by adding an entry to the end of the arch/sh/tools/mach-types
list. The method for doing this is self explanatory, and so we won't waste
space restating it here. After this is done, you will be able to use
implicit checks for your board if you need this somewhere throughout the
common code, such as:
/* Make sure we're on the FooTech Vaporboard */
if (!mach_is_vapor())
return -ENODEV;
also note that the mach_is_boardname() check will be implicitly forced to
lowercase, regardless of the fact that the mach-types entries are all
uppercase. You can read the script if you really care, but it's pretty ugly,
so you probably don't want to do that.
Now all that's left to do is providing a defconfig for your new board. This
way, other people who end up with this board can simply use this config
for reference instead of trying to guess what settings are supposed to be
used on it.
Also, as soon as you have copied over a sample .config for your new board
(assume arch/sh/configs/vapor_defconfig), you can also use this directly as a
build target, and it will be implicitly listed as such in the help text.
Looking at the 'make help' output, you should now see something like:
Architecture specific targets (sh):
zImage - Compressed kernel image (arch/sh/boot/zImage)
adx_defconfig - Build for adx
cqreek_defconfig - Build for cqreek
dreamcast_defconfig - Build for dreamcast
...
vapor_defconfig - Build for vapor
which then allows you to do:
$ make ARCH=sh CROSS_COMPILE=sh4-linux- vapor_defconfig vmlinux
which will in turn copy the defconfig for this board, run it through
oldconfig (prompting you for any new options since the time of creation),
and start you on your way to having a functional kernel for your new
board.

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Notes on register bank usage in the kernel
==========================================
Introduction
------------
The SH-3 and SH-4 CPU families traditionally include a single partial register
bank (selected by SR.RB, only r0 ... r7 are banked), whereas other families
may have more full-featured banking or simply no such capabilities at all.
SR.RB banking
-------------
In the case of this type of banking, banked registers are mapped directly to
r0 ... r7 if SR.RB is set to the bank we are interested in, otherwise ldc/stc
can still be used to reference the banked registers (as r0_bank ... r7_bank)
when in the context of another bank. The developer must keep the SR.RB value
in mind when writing code that utilizes these banked registers, for obvious
reasons. Userspace is also not able to poke at the bank1 values, so these can
be used rather effectively as scratch registers by the kernel.
Presently the kernel uses several of these registers.
- r0_bank, r1_bank (referenced as k0 and k1, used for scratch
registers when doing exception handling).
- r2_bank (used to track the EXPEVT/INTEVT code)
- Used by do_IRQ() and friends for doing irq mapping based off
of the interrupt exception vector jump table offset
- r6_bank (global interrupt mask)
- The SR.IMASK interrupt handler makes use of this to set the
interrupt priority level (used by local_irq_enable())
- r7_bank (current)