.from: https://github.com/leroilion/mbed/blob/master/SDCard/SDFileSystem/SDFileSystem.cpp
--
#include "mbed.h"
#include "SDFileSystem.h"
SDFileSystem sd(p5, p6, p7, p12, "sd");
int main() {
FILE *fp = fopen("/sd/myfile.txt", "w");
fprintf(fp, "Hello World!\n");
fclose(fp);
}
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/* mbed Microcontroller Library - SDFileSystem
* Copyright (c) 2008-2009, sford
*
* Introduction
* ------------
* SD and MMC cards support a number of interfaces, but common to them all
* is one based on SPI. This is the one I'm implmenting because it means
* it is much more portable even though not so performant, and we already
* have the mbed SPI Interface!
*
* The main reference I'm using is Chapter 7, "SPI Mode" of:
* http://www.sdcard.org/developers/tech/sdcard/pls/Simplified_Physical_Layer_Spec.pdf
*
* SPI Startup
* -----------
* The SD card powers up in SD mode. The SPI interface mode is selected by
* asserting CS low and sending the reset command (CMD0). The card will
* respond with a (R1) response.
*
* CMD8 is optionally sent to determine the voltage range supported, and
* indirectly determine whether it is a version 1.x SD/non-SD card or
* version 2.x. I'll just ignore this for now.
*
* ACMD41 is repeatedly issued to initialise the card, until "in idle"
* (bit 0) of the R1 response goes to '0', indicating it is initialised.
*
* You should also indicate whether the host supports High Capicity cards,
* and check whether the card is high capacity - i'll also ignore this
*
* SPI Protocol
* ------------
* The SD SPI protocol is based on transactions made up of 8-bit words, with
* the host starting every bus transaction by asserting the CS signal low. The
* card always responds to commands, data blocks and errors.
*
* The protocol supports a CRC, but by default it is off (except for the
* first reset CMD0, where the CRC can just be pre-calculated, and CMD8)
* I'll leave the CRC off I think!
*
* Standard capacity cards have variable data block sizes, whereas High
* Capacity cards fix the size of data block to 512 bytes. I'll therefore
* just always use the Standard Capacity cards with a block size of 512 bytes.
* This is set with CMD16.
*
* You can read and write single blocks (CMD17, CMD25) or multiple blocks
* (CMD18, CMD25). For simplicity, I'll just use single block accesses. When
* the card gets a read command, it responds with a response token, and then
* a data token or an error.
*
* SPI Command Format
* ------------------
* Commands are 6-bytes long, containing the command, 32-bit argument, and CRC.
*
* +---------------+------------+------------+-----------+----------+--------------+
* | 01 | cmd[5:0] | arg[31:24] | arg[23:16] | arg[15:8] | arg[7:0] | crc[6:0] | 1 |
* +---------------+------------+------------+-----------+----------+--------------+
*
* As I'm not using CRC, I can fix that byte to what is needed for CMD0 (0x95)
*
* All Application Specific commands shall be preceded with APP_CMD (CMD55).
*
* SPI Response Format
* -------------------
* The main response format (R1) is a status byte (normally zero). Key flags:
* idle - 1 if the card is in an idle state/initialising
* cmd - 1 if an illegal command code was detected
*
* +-------------------------------------------------+
* R1 | 0 | arg | addr | seq | crc | cmd | erase | idle |
* +-------------------------------------------------+
*
* R1b is the same, except it is followed by a busy signal (zeros) until
* the first non-zero byte when it is ready again.
*
* Data Response Token
* -------------------
* Every data block written to the card is acknowledged by a byte
* response token
*
* +----------------------+
* | xxx | 0 | status | 1 |
* +----------------------+
* 010 - OK!
* 101 - CRC Error
* 110 - Write Error
*
* Single Block Read and Write
* ---------------------------
*
* Block transfers have a byte header, followed by the data, followed
* by a 16-bit CRC. In our case, the data will always be 512 bytes.
*
* +------+---------+---------+- - - -+---------+-----------+----------+
* | 0xFE | data[0] | data[1] | | data[n] | crc[15:8] | crc[7:0] |
* +------+---------+---------+- - - -+---------+-----------+----------+
*/
#include "SDFileSystem.h"
#define SD_COMMAND_TIMEOUT 5000
SDFileSystem::SDFileSystem(PinName mosi, PinName miso, PinName sclk, PinName cs, const char* name) :
FATFileSystem(name), _spi(mosi, miso, sclk), _cs(cs) {
_cs = 1;
}
int SDFileSystem::disk_initialize() {
_spi.frequency(100000); // Set to 100kHz for initialisation
// Initialise the card by clocking it a bit (cs = 1)
for(int i=0; i<16; i++) {
_spi.write(0xFF);
}
// send CMD0, should return with all zeros except IDLE STATE set (bit 0)
if(_cmd(0, 0) != 0x01) {
fprintf(stderr, "Not in idle state\n");
return 1;
}
// ACMD41 to give host capacity support (repeat until not busy)
// ACMD41 is application specific command, so we send APP_CMD (CMD55) beforehand
for(int i=0;; i++) {
_cmd(55, 0);
int response = _cmd(41, 0);
if(response == 0) {
break;
} else if(i > SD_COMMAND_TIMEOUT) {
fprintf(stderr, "Timeout waiting for card\n");
return 1;
}
}
_sectors = _sd_sectors();
// Set block length to 512 (CMD16)
if(_cmd(16, 512) != 0) {
fprintf(stderr, "Set block timeout\n");
return 1;
}
_spi.frequency(1000000); // Set to 1MHz for data transfer
return 0;
}
int SDFileSystem::disk_write(const char *buffer, int block_number) {
// set write address for single block (CMD24)
if(_cmd(24, block_number * 512) != 0) {
return 1;
}
// send the data block
_write(buffer, 512);
return 0;
}
int SDFileSystem::disk_read(char *buffer, int block_number) {
// set read address for single block (CMD17)
if(_cmd(17, block_number * 512) != 0) {
return 1;
}
// receive the data
_read(buffer, 512);
return 0;
}
int SDFileSystem::disk_status() { return 0; }
int SDFileSystem::disk_sync() { return 0; }
int SDFileSystem::disk_sectors() { return _sectors; }
// PRIVATE FUNCTIONS
int SDFileSystem::_cmd(int cmd, int arg) {
_cs = 0;
// send a command
_spi.write(0x40 | cmd);
_spi.write(arg >> 24);
_spi.write(arg >> 16);
_spi.write(arg >> 8);
_spi.write(arg >> 0);
_spi.write(0x95);
// wait for the repsonse (response[7] == 0)
for(int i=0; i<SD_COMMAND_TIMEOUT; i++) {
int response = _spi.write(0xFF);
if(!(response & 0x80)) {
_cs = 1;
return response;
}
}
_cs = 1;
return -1; // timeout
}
int SDFileSystem::_read(char *buffer, int length) {
_cs = 0;
// read until start byte (0xFF)
while(_spi.write(0xFF) != 0xFE);
// read data
for(int i=0; i<length; i++) {
buffer[i] = _spi.write(0xFF);
}
_spi.write(0xFF); // checksum
_spi.write(0xFF);
_cs = 1;
return 0;
}
int SDFileSystem::_write(const char *buffer, int length) {
_cs = 0;
// indicate start of block
_spi.write(0xFE);
// write the data
for(int i=0; i<length; i++) {
_spi.write(buffer[i]);
}
// write the checksum
_spi.write(0xFF);
_spi.write(0xFF);
// check the repsonse token
if((_spi.write(0xFF) & 0x1F) != 0x05) {
_cs = 1;
return 1;
}
// wait for write to finish
while(_spi.write(0xFF) == 0);
_cs = 1;
return 0;
}
static int ext_bits(char *data, int msb, int lsb) {
int bits = 0;
int size = 1 + msb - lsb;
for(int i=0; i<size; i++) {
int position = lsb + i;
int byte = 15 - (position >> 3);
int bit = position & 0x7;
int value = (data[byte] >> bit) & 1;
bits |= value << i;
}
return bits;
}
int SDFileSystem::_sd_sectors() {
// CMD9, Response R2 (R1 byte + 16-byte block read)
if(_cmd(9, 0) != 0) {
fprintf(stderr, "Didn't get a response from the disk\n");
return 0;
}
char csd[16];
if(_read(csd, 16) != 0) {
fprintf(stderr, "Couldn't read csd response from disk\n");
return 0;
}
// csd_structure : csd[127:126]
// c_size : csd[73:62]
// c_size_mult : csd[49:47]
// read_bl_len : csd[83:80]
int csd_structure = ext_bits(csd, 127, 126);
int c_size = ext_bits(csd, 73, 62);
int c_size_mult = ext_bits(csd, 49, 47);
int read_bl_len = ext_bits(csd, 83, 80);
if(csd_structure != 0) {
fprintf(stderr, "This disk tastes funny! I only know about type 0 CSD structures");
return 0;
}
int blocks = (c_size + 1) * (1 << (c_size_mult + 2));
int block_size = 1 << read_bl_len;
if(block_size != 512) {
fprintf(stderr, "This disk tastes funny! I only like 512-byte blocks");
return 0;
}
return blocks;
}
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/* mbed Microcontroller Library - SDFileSystem
* Copyright (c) 2008-2009, sford
*/
#ifndef SDFILESYSTEM_H
#define SDFILESYSTEM_H
#include "mbed.h"
#include "FATFileSystem.h"
/* Class: SDFileSystem
* Access the filesystem on an SD Card using SPI
*
* Example:
* > SDFileSystem sd(p5, p6, p7, p12, "sd");
* >
* > int main() {
* > FILE *fp = fopen("/sd/myfile.txt", "w");
* > fprintf(fp, "Hello World!\n");
* > fclose(fp);
* > }
*/
class SDFileSystem : public FATFileSystem {
public:
/* Constructor: SDFileSystem
* Create the File System for accessing an SD Card using SPI
*
* Variables:
* mosi - SPI mosi pin connected to SD Card
* miso - SPI miso pin conencted to SD Card
* sclk - SPI sclk pin connected to SD Card
* cs - DigitalOut pin used as SD Card chip select
* name - The name used to access the filesystem
*/
SDFileSystem(PinName mosi, PinName miso, PinName sclk, PinName cs, const char* name);
virtual int disk_initialize();
virtual int disk_write(const char *buffer, int block_number);
virtual int disk_read(char *buffer, int block_number);
virtual int disk_status();
virtual int disk_sync();
virtual int disk_sectors();
protected:
int _cmd(int cmd, int arg);
int _read(char *buffer, int length);
int _write(const char *buffer, int length);
int _sd_sectors();
int _sectors;
SPI _spi;
DigitalOut _cs;
};
#endif
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