137 lines
3.6 KiB
C
137 lines
3.6 KiB
C
/* sd2snes - SD card based universal cartridge for the SNES
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Copyright (C) 2009-2010 Maximilian Rehkopf <otakon@gmx.net>
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This file was adapted from sd2iec, written by Ingo Korb.
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Original copyright header follows:
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*/
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/* sd2iec - SD/MMC to Commodore serial bus interface/controller
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Copyright (C) 2007-2009 Ingo Korb <ingo@akana.de>
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Inspiration and low-level SD/MMC access based on code from MMC2IEC
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by Lars Pontoppidan et al., see sdcard.c|h and config.h.
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FAT filesystem access based on code from ChaN and Jim Brain, see ff.c|h.
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; version 2 of the License only.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program; if not, write to the Free Software
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Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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spi.c: Low level SPI access
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Extended, optimized and cleaned version of code from MMC2IEC,
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original copyright header follows:
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//
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// Title : SPI module
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// Author : Lars Pontoppidan
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// Date : January, 2007
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// Version : 1.03
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// Target MCU : Atmel AVR Series
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//
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// DESCRIPTION:
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// This module implements initialization, sending and receiving bytes using
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// hardware SPI on an AVR.
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//
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// DISCLAIMER:
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// The author is in no way responsible for any problems or damage caused by
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// using this code. Use at your own risk.
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//
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// LICENSE:
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// This code is distributed under the GNU Public License
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// which can be found at http://www.gnu.org/licenses/gpl.txt
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//
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*/
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// FIXME: Integrate into sdcard.c
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#include <avr/io.h>
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#include "avrcompat.h"
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#include "spi.h"
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// access routines
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void spiInit(void)
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{
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volatile uint8_t dummy;
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// setup SPI I/O pins
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SPI_PORT = (SPI_PORT & ~SPI_MASK) | SPI_SCK | SPI_SS | SPI_MISO;
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SPI_DDR = (SPI_DDR & ~SPI_MASK) | SPI_SCK | SPI_SS | SPI_MOSI;
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// setup SPI interface:
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// interrupts disabled, SPI enabled, MSB first, master mode,
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// leading edge rising, sample on leading edge, clock = f/4
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SPCR = 0b01010000;
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// Enable SPI double speed mode -> clock = f/2
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SPSR = _BV(SPI2X);
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// clear status
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dummy = SPSR;
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// clear receive buffer
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dummy = SPDR;
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}
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inline uint8_t spiTransferByte(uint8_t data)
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{
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// send the given data
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SPDR = data;
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// wait for transfer to complete
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loop_until_bit_is_set(SPSR, SPIF);
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// *** reading of the SPSR and SPDR are crucial
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// *** to the clearing of the SPIF flag
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// *** in non-interrupt mode
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// return the received data
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return SPDR;
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}
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inline uint32_t spiTransferLong(const uint32_t data)
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{
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// It seems to be necessary to use the union in order to get efficient
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// assembler code.
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// Beware, endian unsafe union
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union {
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uint32_t l;
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uint8_t c[4];
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} long2char;
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long2char.l = data;
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// send the given data
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SPDR = long2char.c[3];
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// wait for transfer to complete
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loop_until_bit_is_set(SPSR, SPIF);
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long2char.c[3] = SPDR;
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SPDR = long2char.c[2];
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// wait for transfer to complete
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loop_until_bit_is_set(SPSR, SPIF);
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long2char.c[2] = SPDR;
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SPDR = long2char.c[1];
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// wait for transfer to complete
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loop_until_bit_is_set(SPSR, SPIF);
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long2char.c[1] = SPDR;
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SPDR = long2char.c[0];
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// wait for transfer to complete
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loop_until_bit_is_set(SPSR, SPIF);
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long2char.c[0] = SPDR;
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return long2char.l;
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}
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