SDFileSystem.cpp

00001 /* mbed Microcontroller Library - SDFileSystem
00002  * Copyright (c) 2008-2009, sford
00003  *
00004  * Introduction
00005  * ------------
00006  * SD and MMC cards support a number of interfaces, but common to them all
00007  * is one based on SPI. This is the one I'm implmenting because it means
00008  * it is much more portable even though not so performant, and we already 
00009  * have the mbed SPI Interface!
00010  *
00011  * The main reference I'm using is Chapter 7, "SPI Mode" of: 
00012  *  http://www.sdcard.org/developers/tech/sdcard/pls/Simplified_Physical_Layer_Spec.pdf
00013  *
00014  * SPI Startup
00015  * -----------
00016  * The SD card powers up in SD mode. The SPI interface mode is selected by
00017  * asserting CS low and sending the reset command (CMD0). The card will 
00018  * respond with a (R1) response.
00019  *
00020  * CMD8 is optionally sent to determine the voltage range supported, and 
00021  * indirectly determine whether it is a version 1.x SD/non-SD card or 
00022  * version 2.x. I'll just ignore this for now.
00023  *
00024  * ACMD41 is repeatedly issued to initialise the card, until "in idle"
00025  * (bit 0) of the R1 response goes to '0', indicating it is initialised.
00026  *
00027  * You should also indicate whether the host supports High Capicity cards,
00028  * and check whether the card is high capacity - i'll also ignore this
00029  *
00030  * SPI Protocol
00031  * ------------
00032  * The SD SPI protocol is based on transactions made up of 8-bit words, with
00033  * the host starting every bus transaction by asserting the CS signal low. The
00034  * card always responds to commands, data blocks and errors.
00035  * 
00036  * The protocol supports a CRC, but by default it is off (except for the 
00037  * first reset CMD0, where the CRC can just be pre-calculated, and CMD8)
00038  * I'll leave the CRC off I think! 
00039  * 
00040  * Standard capacity cards have variable data block sizes, whereas High 
00041  * Capacity cards fix the size of data block to 512 bytes. I'll therefore
00042  * just always use the Standard Capacity cards with a block size of 512 bytes.
00043  * This is set with CMD16.
00044  *
00045  * You can read and write single blocks (CMD17, CMD25) or multiple blocks 
00046  * (CMD18, CMD25). For simplicity, I'll just use single block accesses. When
00047  * the card gets a read command, it responds with a response token, and then 
00048  * a data token or an error.
00049  * 
00050  * SPI Command Format
00051  * ------------------
00052  * Commands are 6-bytes long, containing the command, 32-bit argument, and CRC.
00053  *
00054  * +---------------+------------+------------+-----------+----------+--------------+
00055  * | 01 | cmd[5:0] | arg[31:24] | arg[23:16] | arg[15:8] | arg[7:0] | crc[6:0] | 1 |
00056  * +---------------+------------+------------+-----------+----------+--------------+
00057  *
00058  * As I'm not using CRC, I can fix that byte to what is needed for CMD0 (0x95)
00059  *
00060  * All Application Specific commands shall be preceded with APP_CMD (CMD55).
00061  *
00062  * SPI Response Format
00063  * -------------------
00064  * The main response format (R1) is a status byte (normally zero). Key flags:
00065  *  idle - 1 if the card is in an idle state/initialising 
00066  *  cmd  - 1 if an illegal command code was detected
00067  *
00068  *    +-------------------------------------------------+
00069  * R1 | 0 | arg | addr | seq | crc | cmd | erase | idle |
00070  *    +-------------------------------------------------+
00071  *
00072  * R1b is the same, except it is followed by a busy signal (zeros) until
00073  * the first non-zero byte when it is ready again.
00074  *
00075  * Data Response Token
00076  * -------------------
00077  * Every data block written to the card is acknowledged by a byte 
00078  * response token
00079  *
00080  * +----------------------+
00081  * | xxx | 0 | status | 1 |
00082  * +----------------------+
00083  *              010 - OK!
00084  *              101 - CRC Error
00085  *              110 - Write Error
00086  *
00087  * Single Block Read and Write
00088  * ---------------------------
00089  *
00090  * Block transfers have a byte header, followed by the data, followed
00091  * by a 16-bit CRC. In our case, the data will always be 512 bytes.
00092  *  
00093  * +------+---------+---------+- -  - -+---------+-----------+----------+
00094  * | 0xFE | data[0] | data[1] |        | data[n] | crc[15:8] | crc[7:0] | 
00095  * +------+---------+---------+- -  - -+---------+-----------+----------+
00096  */
00097  
00098 #include "SDFileSystem.h"
00099 
00100 #define SD_COMMAND_TIMEOUT 5000
00101 
00102 //#define CR "\n"
00103 #define CR "\r\n"
00104 
00105 SDFileSystem::SDFileSystem(PinName mosi, PinName miso, PinName sclk, PinName cs, const char* name) :
00106   FATFileSystem(name), _spi(mosi, miso, sclk), _cs(cs) {
00107       _cs = 1; 
00108 }
00109 
00110 #define R1_IDLE_STATE           (1 << 0)
00111 #define R1_ERASE_RESET          (1 << 1)
00112 #define R1_ILLEGAL_COMMAND      (1 << 2)
00113 #define R1_COM_CRC_ERROR        (1 << 3)
00114 #define R1_ERASE_SEQUENCE_ERROR (1 << 4)
00115 #define R1_ADDRESS_ERROR        (1 << 5)
00116 #define R1_PARAMETER_ERROR      (1 << 6)
00117 
00118 int SDFileSystem::disk_initialize() {
00119 
00120     _spi.frequency(100000); // Set to 100kHz for initialisation
00121     
00122     // Initialise the card by clocking it a bit (cs = 1)
00123     _cs = 1;
00124     for(int i=0; i<16; i++) {   
00125         _spi.write(0xFF);
00126     }
00127 
00128     // send CMD0, should return with all zeros except IDLE STATE set (bit 0)
00129     if(_cmd(0, 0) != R1_IDLE_STATE) { 
00130         fprintf(stderr, "No disk, or could not put SD card into SPI idle state" CR);
00131         return 1;
00132     }
00133 
00134     int r = _cmd8();
00135     if(r == R1_IDLE_STATE) {
00136         printf("SD version 2.x" CR);
00137     } else if(r == (R1_IDLE_STATE | R1_ILLEGAL_COMMAND)) {
00138         printf("SD version 1.x" CR);
00139     } else {
00140         error("Unknown SD version" CR);
00141     }
00142     
00143     // ACMD41 to give host capacity support (repeat until not busy)
00144     // ACMD41 is application specific command, so we send APP_CMD (CMD55) beforehand
00145     for(int i=0;; i++) {
00146         _cmd(55, 0); 
00147         int response = _cmd(41, 0);
00148         if(response == 0) { 
00149             break;
00150         } else if(i > SD_COMMAND_TIMEOUT) {
00151             fprintf(stderr, "Timeout waiting for card" CR);
00152             return 1;
00153         }    
00154     }
00155 
00156 //    printf("OK" CR);
00157 
00158     _sectors = _sd_sectors();
00159 
00160     // Set block length to 512 (CMD16)
00161     if(_cmd(16, 512) != 0) {
00162         fprintf(stderr, "Set block timeout" CR);
00163         return 1;
00164     }
00165         
00166     _spi.frequency(1000000); // Set to 1MHz for data transfer
00167     return 0;
00168 }
00169 
00170 int SDFileSystem::disk_write(const char *buffer, int block_number) {
00171     // set write address for single block (CMD24)
00172     if(_cmd(24, block_number * 512) != 0) {
00173         return 1;
00174     }
00175 
00176     // send the data block
00177     _write(buffer, 512);    
00178     return 0;    
00179 }
00180 
00181 int SDFileSystem::disk_read(char *buffer, int block_number) {        
00182     // set read address for single block (CMD17)
00183     if(_cmd(17, block_number * 512) != 0) {
00184         return 1;
00185     }
00186     
00187     // receive the data
00188     _read(buffer, 512);
00189     return 0;
00190 }
00191 
00192 int SDFileSystem::disk_status() { return 0; }
00193 int SDFileSystem::disk_sync() { return 0; }
00194 int SDFileSystem::disk_sectors() { return _sectors; }
00195 
00196 // PRIVATE FUNCTIONS
00197 
00198 int SDFileSystem::_cmd(int cmd, int arg) {
00199     _cs = 0; 
00200 
00201     // send a command
00202     _spi.write(0x40 | cmd);
00203     _spi.write(arg >> 24);
00204     _spi.write(arg >> 16);
00205     _spi.write(arg >> 8);
00206     _spi.write(arg >> 0);
00207     _spi.write(0x95);
00208 
00209     // wait for the repsonse (response[7] == 0)
00210     for(int i=0; i<SD_COMMAND_TIMEOUT; i++) {
00211         int response = _spi.write(0xFF);
00212         if(!(response & 0x80)) {
00213             _cs = 1;
00214             _spi.write(0xFF);
00215             return response;
00216         }
00217     }
00218     _cs = 1;
00219     _spi.write(0xFF);
00220     return -1; // timeout
00221 }
00222 
00223 int SDFileSystem::_cmd8() {
00224     _cs = 0; 
00225     
00226     // send a command
00227     _spi.write(0x40 | 8); // CMD8
00228     _spi.write(0x00);     // reserved
00229     _spi.write(0x00);     // reserved
00230     _spi.write(0x01);     // 3.3v
00231     _spi.write(0xAA);     // check pattern
00232     _spi.write(0x87);     // crc
00233 
00234     // wait for the repsonse (response[7] == 0)
00235     for(int i=0; i<SD_COMMAND_TIMEOUT * 1000; i++) {
00236         char response[5];
00237         response[0] = _spi.write(0xFF);
00238         if(!(response[0] & 0x80)) {
00239                 for(int j=1; j<5; j++) {
00240                     response[i] = _spi.write(0xFF);
00241                 }
00242                 _cs = 1;
00243                 _spi.write(0xFF);
00244                 return response[0];
00245         }
00246     }
00247     _cs = 1;
00248     _spi.write(0xFF);
00249     return -1; // timeout
00250 }
00251 
00252 int SDFileSystem::_read(char *buffer, int length) {
00253     _cs = 0;
00254 
00255     // read until start byte (0xFF)
00256     while(_spi.write(0xFF) != 0xFE);
00257 
00258     // read data
00259     for(int i=0; i<length; i++) {
00260         buffer[i] = _spi.write(0xFF);
00261     }
00262     _spi.write(0xFF); // checksum
00263     _spi.write(0xFF);
00264 
00265     _cs = 1;    
00266     _spi.write(0xFF);
00267     return 0;
00268 }
00269 
00270 int SDFileSystem::_write(const char *buffer, int length) {
00271     _cs = 0;
00272     
00273     // indicate start of block
00274     _spi.write(0xFE);
00275     
00276     // write the data
00277     for(int i=0; i<length; i++) {
00278         _spi.write(buffer[i]);
00279     }
00280     
00281     // write the checksum
00282     _spi.write(0xFF); 
00283     _spi.write(0xFF);
00284 
00285     // check the repsonse token
00286     if((_spi.write(0xFF) & 0x1F) != 0x05) {
00287         _cs = 1; 
00288         _spi.write(0xFF);        
00289         return 1;
00290     }
00291 
00292     // wait for write to finish
00293     while(_spi.write(0xFF) == 0);
00294 
00295     _cs = 1; 
00296     _spi.write(0xFF);
00297     return 0;
00298 }
00299 
00300 static int ext_bits(char *data, int msb, int lsb) {
00301     int bits = 0;
00302     int size = 1 + msb - lsb; 
00303     for(int i=0; i<size; i++) {
00304         int position = lsb + i;
00305         int byte = 15 - (position >> 3);
00306         int bit = position & 0x7;
00307         int value = (data[byte] >> bit) & 1;
00308         bits |= value << i;
00309     }
00310     return bits;
00311 }
00312 
00313 int SDFileSystem::_sd_sectors() {
00314 
00315     // CMD9, Response R2 (R1 byte + 16-byte block read)
00316     if(_cmd(9, 0) != 0) {
00317         fprintf(stderr, "Didn't get a response from the disk" CR);
00318         return 0;
00319     }
00320     
00321     char csd[16];    
00322     if(_read(csd, 16) != 0) {
00323         fprintf(stderr, "Couldn't read csd response from disk" CR);
00324         return 0;
00325     }
00326 
00327     // csd_structure : csd[127:126]
00328     // c_size        : csd[73:62]
00329     // c_size_mult   : csd[49:47]
00330     // read_bl_len   : csd[83:80] 
00331 
00332     int csd_structure = ext_bits(csd, 127, 126);
00333     int c_size = ext_bits(csd, 73, 62);
00334     int c_size_mult = ext_bits(csd, 49, 47);
00335     int read_bl_len = ext_bits(csd, 83, 80);
00336     
00337     if(csd_structure != 0) {
00338         fprintf(stderr, "This disk tastes funny! I only know about type 0 CSD structures" CR);
00339         // Non-zero is SDHC.
00340         return 0;
00341     }
00342                             
00343     int blocks = (c_size + 1) * (1 << (c_size_mult + 2));
00344     int block_size = 1 << read_bl_len;
00345 
00346     if (block_size != 512 && block_size != 1024) {
00347         fprintf(stderr, "This disk tastes funny! %d byte block. I only like 512 or 1024 -byte blocks" CR, block_size);
00348         return 0;
00349     }
00350     
00351     return blocks;
00352 }