SDFileSystem.cpp

00001 /* mbed Microcontroller Library - SDFileSystem
00002  * Copyright (c) 2008-2009, sford
00003  */
00004  
00005 // VERY DRAFT CODE! Needs serious rework/refactoring 
00006  
00007 /* Introduction
00008  * ------------
00009  * SD and MMC cards support a number of interfaces, but common to them all
00010  * is one based on SPI. This is the one I'm implmenting because it means
00011  * it is much more portable even though not so performant, and we already 
00012  * have the mbed SPI Interface!
00013  *
00014  * The main reference I'm using is Chapter 7, "SPI Mode" of: 
00015  *  http://www.sdcard.org/developers/tech/sdcard/pls/Simplified_Physical_Layer_Spec.pdf
00016  *
00017  * SPI Startup
00018  * -----------
00019  * The SD card powers up in SD mode. The SPI interface mode is selected by
00020  * asserting CS low and sending the reset command (CMD0). The card will 
00021  * respond with a (R1) response.
00022  *
00023  * CMD8 is optionally sent to determine the voltage range supported, and 
00024  * indirectly determine whether it is a version 1.x SD/non-SD card or 
00025  * version 2.x. I'll just ignore this for now.
00026  *
00027  * ACMD41 is repeatedly issued to initialise the card, until "in idle"
00028  * (bit 0) of the R1 response goes to '0', indicating it is initialised.
00029  *
00030  * You should also indicate whether the host supports High Capicity cards,
00031  * and check whether the card is high capacity - i'll also ignore this
00032  *
00033  * SPI Protocol
00034  * ------------
00035  * The SD SPI protocol is based on transactions made up of 8-bit words, with
00036  * the host starting every bus transaction by asserting the CS signal low. The
00037  * card always responds to commands, data blocks and errors.
00038  * 
00039  * The protocol supports a CRC, but by default it is off (except for the 
00040  * first reset CMD0, where the CRC can just be pre-calculated, and CMD8)
00041  * I'll leave the CRC off I think! 
00042  * 
00043  * Standard capacity cards have variable data block sizes, whereas High 
00044  * Capacity cards fix the size of data block to 512 bytes. I'll therefore
00045  * just always use the Standard Capacity cards with a block size of 512 bytes.
00046  * This is set with CMD16.
00047  *
00048  * You can read and write single blocks (CMD17, CMD25) or multiple blocks 
00049  * (CMD18, CMD25). For simplicity, I'll just use single block accesses. When
00050  * the card gets a read command, it responds with a response token, and then 
00051  * a data token or an error.
00052  * 
00053  * SPI Command Format
00054  * ------------------
00055  * Commands are 6-bytes long, containing the command, 32-bit argument, and CRC.
00056  *
00057  * +---------------+------------+------------+-----------+----------+--------------+
00058  * | 01 | cmd[5:0] | arg[31:24] | arg[23:16] | arg[15:8] | arg[7:0] | crc[6:0] | 1 |
00059  * +---------------+------------+------------+-----------+----------+--------------+
00060  *
00061  * As I'm not using CRC, I can fix that byte to what is needed for CMD0 (0x95)
00062  *
00063  * All Application Specific commands shall be preceded with APP_CMD (CMD55).
00064  *
00065  * SPI Response Format
00066  * -------------------
00067  * The main response format (R1) is a status byte (normally zero). Key flags:
00068  *  idle - 1 if the card is in an idle state/initialising 
00069  *  cmd  - 1 if an illegal command code was detected
00070  *
00071  *    +-------------------------------------------------+
00072  * R1 | 0 | arg | addr | seq | crc | cmd | erase | idle |
00073  *    +-------------------------------------------------+
00074  *
00075  * R1b is the same, except it is followed by a busy signal (zeros) until
00076  * the first non-zero byte when it is ready again.
00077  *
00078  * Data Response Token
00079  * -------------------
00080  * Every data block written to the card is acknowledged by a byte 
00081  * response token
00082  *
00083  * +----------------------+
00084  * | xxx | 0 | status | 1 |
00085  * +----------------------+
00086  *              010 - OK!
00087  *              101 - CRC Error
00088  *              110 - Write Error
00089  *
00090  * Single Block Read and Write
00091  * ---------------------------
00092  *
00093  * Block transfers have a byte header, followed by the data, followed
00094  * by a 16-bit CRC. In our case, the data will always be 512 bytes.
00095  *  
00096  * +------+---------+---------+- -  - -+---------+-----------+----------+
00097  * | 0xFE | data[0] | data[1] |        | data[n] | crc[15:8] | crc[7:0] | 
00098  * +------+---------+---------+- -  - -+---------+-----------+----------+
00099  */
00100  
00101 #include "SDFileSystem.h"
00102 
00103 #define SD_COMMAND_TIMEOUT 5000
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 // Types
00119 //  - v1.x Standard Capacity
00120 //  - v2.x Standard Capacity
00121 //  - v2.x High Capacity
00122 //  - Not recognised as an SD Card
00123 
00124 #define SDCARD_FAIL 0
00125 #define SDCARD_V1   1
00126 #define SDCARD_V2   2
00127 #define SDCARD_V2HC 3
00128 
00129 int SDFileSystem::initialise_card() {
00130     // Set to 100kHz for initialisation, and clock card with cs = 1
00131     _spi.frequency(400000); 
00132     _cs = 1;
00133     for(int i=0; i<16; i++) {   
00134         _spi.write(0xFF);
00135     }
00136 
00137     // send CMD0, should return with all zeros except IDLE STATE set (bit 0)
00138     _cmd(0, 0);
00139     if(_cmd(0, 0) != R1_IDLE_STATE) { 
00140         fprintf(stderr, "No disk, or could not put SD card in to SPI idle state\n");
00141         return SDCARD_FAIL;
00142     }
00143 
00144     // send CMD8 to determine whther it is ver 2.x
00145     int r = _cmd8();
00146     if(r == R1_IDLE_STATE) {
00147         return initialise_card_v2();
00148     } else if(r == (R1_IDLE_STATE | R1_ILLEGAL_COMMAND)) {
00149         return initialise_card_v1();
00150     } else {
00151         fprintf(stderr, "Not in idle state after sending CMD8 (not an SD card?)\n");
00152         return SDCARD_FAIL;
00153     }
00154 }
00155 
00156 int SDFileSystem::initialise_card_v1() {
00157     for(int i=0; i<SD_COMMAND_TIMEOUT; i++) {
00158         _cmd(55, 0); 
00159         if(_cmd(41, 0) == 0) { 
00160             return SDCARD_V1;
00161         }
00162     }
00163 
00164     fprintf(stderr, "Timeout waiting for v1.x card\n");
00165     return SDCARD_FAIL;
00166 }
00167 
00168 int SDFileSystem::initialise_card_v2() {
00169     
00170     for(int i=0; i<SD_COMMAND_TIMEOUT; i++) {
00171         _cmd(55, 0); 
00172         if(_cmd(41, 0) == 0) { 
00173             _cmd58();
00174             return SDCARD_V2;
00175         }
00176     }
00177 
00178     fprintf(stderr, "Timeout waiting for v2.x card\n");
00179     return SDCARD_FAIL;
00180 }
00181 
00182 int SDFileSystem::disk_initialize() {
00183 
00184     int i = initialise_card();
00185 //    printf("init card = %d\n", i);
00186 //    printf("OK\n");
00187 
00188     _sectors = _sd_sectors();
00189 
00190     // Set block length to 512 (CMD16)
00191     if(_cmd(16, 512) != 0) {
00192         fprintf(stderr, "Set 512-byte block timed out\n");
00193         return 1;
00194     }
00195         
00196     _spi.frequency(1000000); // Set to 1MHz for data transfer
00197     return 0;
00198 }
00199 
00200 int SDFileSystem::disk_write(const char *buffer, int block_number) {
00201     // set write address for single block (CMD24)
00202     if(_cmd(24, block_number * 512) != 0) {
00203         return 1;
00204     }
00205 
00206     // send the data block
00207     _write(buffer, 512);    
00208     return 0;    
00209 }
00210 
00211 int SDFileSystem::disk_read(char *buffer, int block_number) {        
00212     // set read address for single block (CMD17)
00213     if(_cmd(17, block_number * 512) != 0) {
00214         return 1;
00215     }
00216     
00217     // receive the data
00218     _read(buffer, 512);
00219     return 0;
00220 }
00221 
00222 int SDFileSystem::disk_status() { return 0; }
00223 int SDFileSystem::disk_sync() { return 0; }
00224 int SDFileSystem::disk_sectors() { return _sectors; }
00225 
00226 // PRIVATE FUNCTIONS
00227 
00228 int SDFileSystem::_cmd(int cmd, int arg) {
00229     _cs = 0; 
00230 
00231     // send a command
00232     _spi.write(0x40 | cmd);
00233     _spi.write(arg >> 24);
00234     _spi.write(arg >> 16);
00235     _spi.write(arg >> 8);
00236     _spi.write(arg >> 0);
00237     _spi.write(0x95);
00238 
00239     // wait for the repsonse (response[7] == 0)
00240     for(int i=0; i<SD_COMMAND_TIMEOUT; i++) {
00241         int response = _spi.write(0xFF);
00242         if(!(response & 0x80)) {
00243             _cs = 1;
00244             _spi.write(0xFF);
00245             return response;
00246         }
00247     }
00248     _cs = 1;
00249     _spi.write(0xFF);
00250     return -1; // timeout
00251 }
00252 int SDFileSystem::_cmdx(int cmd, int arg) {
00253     _cs = 0; 
00254 
00255     // send a command
00256     _spi.write(0x40 | cmd);
00257     _spi.write(arg >> 24);
00258     _spi.write(arg >> 16);
00259     _spi.write(arg >> 8);
00260     _spi.write(arg >> 0);
00261     _spi.write(0x95);
00262 
00263     // wait for the repsonse (response[7] == 0)
00264     for(int i=0; i<SD_COMMAND_TIMEOUT; i++) {
00265         int response = _spi.write(0xFF);
00266         if(!(response & 0x80)) {
00267             return response;
00268         }
00269     }
00270     _cs = 1;
00271     _spi.write(0xFF);
00272     return -1; // timeout
00273 }
00274 
00275 
00276 int SDFileSystem::_cmd58() {
00277     _cs = 0; 
00278     int arg = 0;
00279     
00280     // send a command
00281     _spi.write(0x40 | 58);
00282     _spi.write(arg >> 24);
00283     _spi.write(arg >> 16);
00284     _spi.write(arg >> 8);
00285     _spi.write(arg >> 0);
00286     _spi.write(0x95);
00287 
00288     // wait for the repsonse (response[7] == 0)
00289     for(int i=0; i<SD_COMMAND_TIMEOUT; i++) {
00290         int response = _spi.write(0xFF);
00291         if(!(response & 0x80)) {
00292             int ocr = _spi.write(0xFF) << 24;
00293             ocr |= _spi.write(0xFF) << 16;
00294             ocr |= _spi.write(0xFF) << 8;
00295             ocr |= _spi.write(0xFF) << 0;
00296 //            printf("OCR = 0x%08X\n", ocr);
00297             _cs = 1;
00298             _spi.write(0xFF);
00299             return response;
00300         }
00301     }
00302     _cs = 1;
00303     _spi.write(0xFF);
00304     return -1; // timeout
00305 }
00306 
00307 int SDFileSystem::_cmd8() {
00308     _cs = 0; 
00309     
00310     // send a command
00311     _spi.write(0x40 | 8); // CMD8
00312     _spi.write(0x00);     // reserved
00313     _spi.write(0x00);     // reserved
00314     _spi.write(0x01);     // 3.3v
00315     _spi.write(0xAA);     // check pattern
00316     _spi.write(0x87);     // crc
00317 
00318     // wait for the repsonse (response[7] == 0)
00319     for(int i=0; i<SD_COMMAND_TIMEOUT * 1000; i++) {
00320         char response[5];
00321         response[0] = _spi.write(0xFF);
00322         if(!(response[0] & 0x80)) {
00323                 for(int j=1; j<5; j++) {
00324                     response[i] = _spi.write(0xFF);
00325                 }
00326                 _cs = 1;
00327                 _spi.write(0xFF);
00328                 return response[0];
00329         }
00330     }
00331     _cs = 1;
00332     _spi.write(0xFF);
00333     return -1; // timeout
00334 }
00335 
00336 int SDFileSystem::_read(char *buffer, int length) {
00337     _cs = 0;
00338 
00339     // read until start byte (0xFF)
00340     while(_spi.write(0xFF) != 0xFE);
00341 
00342     // read data
00343     for(int i=0; i<length; i++) {
00344         buffer[i] = _spi.write(0xFF);
00345     }
00346     _spi.write(0xFF); // checksum
00347     _spi.write(0xFF);
00348 
00349     _cs = 1;    
00350     _spi.write(0xFF);
00351     return 0;
00352 }
00353 
00354 int SDFileSystem::_write(const char *buffer, int length) {
00355     _cs = 0;
00356     
00357     // indicate start of block
00358     _spi.write(0xFE);
00359     
00360     // write the data
00361     for(int i=0; i<length; i++) {
00362         _spi.write(buffer[i]);
00363     }
00364     
00365     // write the checksum
00366     _spi.write(0xFF); 
00367     _spi.write(0xFF);
00368 
00369     // check the repsonse token
00370     if((_spi.write(0xFF) & 0x1F) != 0x05) {
00371         _cs = 1;
00372         _spi.write(0xFF);        
00373         return 1;
00374     }
00375 
00376     // wait for write to finish
00377     while(_spi.write(0xFF) == 0);
00378 
00379     _cs = 1; 
00380     _spi.write(0xFF);
00381     return 0;
00382 }
00383 
00384 static int ext_bits(char *data, int msb, int lsb) {
00385     int bits = 0;
00386     int size = 1 + msb - lsb; 
00387     for(int i=0; i<size; i++) {
00388         int position = lsb + i;
00389         int byte = 15 - (position >> 3);
00390         int bit = position & 0x7;
00391         int value = (data[byte] >> bit) & 1;
00392         bits |= value << i;
00393     }
00394     return bits;
00395 }
00396 
00397 int SDFileSystem::_sd_sectors() {
00398 
00399     // CMD9, Response R2 (R1 byte + 16-byte block read)
00400     if(_cmdx(9, 0) != 0) {
00401         fprintf(stderr, "Didn't get a response from the disk\n");
00402         return 0;
00403     }
00404     
00405     char csd[16];    
00406     if(_read(csd, 16) != 0) {
00407         fprintf(stderr, "Couldn't read csd response from disk\n");
00408         return 0;
00409     }
00410 
00411     // csd_structure : csd[127:126]
00412     // c_size        : csd[73:62]
00413     // c_size_mult   : csd[49:47]
00414     // read_bl_len   : csd[83:80] - the *maximum* read block length
00415 
00416     int csd_structure = ext_bits(csd, 127, 126);
00417     int c_size = ext_bits(csd, 73, 62);
00418     int c_size_mult = ext_bits(csd, 49, 47);
00419     int read_bl_len = ext_bits(csd, 83, 80);
00420 
00421 //    printf("CSD_STRUCT = %d\n", csd_structure);
00422     
00423     if(csd_structure != 0) {
00424         fprintf(stderr, "This disk tastes funny! I only know about type 0 CSD structures\n");
00425         return 0;
00426     }
00427              
00428     // memory capacity = BLOCKNR * BLOCK_LEN
00429     // where
00430     //  BLOCKNR = (C_SIZE+1) * MULT
00431     //  MULT = 2^(C_SIZE_MULT+2) (C_SIZE_MULT < 8)
00432     //  BLOCK_LEN = 2^READ_BL_LEN, (READ_BL_LEN < 12)         
00433                             
00434     int block_len = 1 << read_bl_len;
00435     int mult = 1 << (c_size_mult + 2);
00436     int blocknr = (c_size + 1) * mult;
00437     int capacity = blocknr * block_len;
00438         
00439     int blocks = capacity / 512;
00440         
00441     return blocks;
00442 }