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(100000); 
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     if(_cmd(0, 0) != R1_IDLE_STATE) { 
00139         fprintf(stderr, "No disk, or could not put SD card in to SPI idle state\n");
00140         return SDCARD_FAIL;
00141     }
00142 
00143     // send CMD8 to determine whther it is ver 2.x
00144     int r = _cmd8();
00145     if(r == R1_IDLE_STATE) {
00146         return initialise_card_v2();
00147     } else if(r == (R1_IDLE_STATE | R1_ILLEGAL_COMMAND)) {
00148         return initialise_card_v1();
00149     } else {
00150         fprintf(stderr, "Not in idle state after sending CMD8 (not an SD card?)\n");
00151         return SDCARD_FAIL;
00152     }
00153 }
00154 
00155 int SDFileSystem::initialise_card_v1() {
00156     for(int i=0; i<SD_COMMAND_TIMEOUT; i++) {
00157         _cmd(55, 0); 
00158         if(_cmd(41, 0) == 0) { 
00159             return SDCARD_V1;
00160         }
00161     }
00162 
00163     fprintf(stderr, "Timeout waiting for v1.x card\n");
00164     return SDCARD_FAIL;
00165 }
00166 
00167 int SDFileSystem::initialise_card_v2() {
00168     
00169     for(int i=0; i<SD_COMMAND_TIMEOUT; i++) {
00170         _cmd(55, 0); 
00171         if(_cmd(41, 0) == 0) { 
00172             _cmd58();
00173             return SDCARD_V2;
00174         }
00175     }
00176 
00177     fprintf(stderr, "Timeout waiting for v2.x card\n");
00178     return SDCARD_FAIL;
00179 }
00180 
00181 int SDFileSystem::disk_initialize() {
00182 
00183     int i = initialise_card();
00184 //    printf("init card = %d\n", i);
00185 //    printf("OK\n");
00186 
00187     _sectors = _sd_sectors();
00188 
00189     // Set block length to 512 (CMD16)
00190     if(_cmd(16, 512) != 0) {
00191         fprintf(stderr, "Set 512-byte block timed out\n");
00192         return 1;
00193     }
00194         
00195     _spi.frequency(1000000); // Set to 1MHz for data transfer
00196     return 0;
00197 }
00198 
00199 int SDFileSystem::disk_write(const char *buffer, int block_number) {
00200     // set write address for single block (CMD24)
00201     if(_cmd(24, block_number * 512) != 0) {
00202         return 1;
00203     }
00204 
00205     // send the data block
00206     _write(buffer, 512);    
00207     return 0;    
00208 }
00209 
00210 int SDFileSystem::disk_read(char *buffer, int block_number) {        
00211     // set read address for single block (CMD17)
00212     if(_cmd(17, block_number * 512) != 0) {
00213         return 1;
00214     }
00215     
00216     // receive the data
00217     _read(buffer, 512);
00218     return 0;
00219 }
00220 
00221 int SDFileSystem::disk_status() { return 0; }
00222 int SDFileSystem::disk_sync() { return 0; }
00223 int SDFileSystem::disk_sectors() { return _sectors; }
00224 
00225 // PRIVATE FUNCTIONS
00226 
00227 int SDFileSystem::_cmd(int cmd, int arg) {
00228     _cs = 0; 
00229 
00230     // send a command
00231     _spi.write(0x40 | cmd);
00232     _spi.write(arg >> 24);
00233     _spi.write(arg >> 16);
00234     _spi.write(arg >> 8);
00235     _spi.write(arg >> 0);
00236     _spi.write(0x95);
00237 
00238     // wait for the repsonse (response[7] == 0)
00239     for(int i=0; i<SD_COMMAND_TIMEOUT; i++) {
00240         int response = _spi.write(0xFF);
00241         if(!(response & 0x80)) {
00242             _cs = 1;
00243             _spi.write(0xFF);
00244             return response;
00245         }
00246     }
00247     _cs = 1;
00248     _spi.write(0xFF);
00249     return -1; // timeout
00250 }
00251 int SDFileSystem::_cmdx(int cmd, int arg) {
00252     _cs = 0; 
00253 
00254     // send a command
00255     _spi.write(0x40 | cmd);
00256     _spi.write(arg >> 24);
00257     _spi.write(arg >> 16);
00258     _spi.write(arg >> 8);
00259     _spi.write(arg >> 0);
00260     _spi.write(0x95);
00261 
00262     // wait for the repsonse (response[7] == 0)
00263     for(int i=0; i<SD_COMMAND_TIMEOUT; i++) {
00264         int response = _spi.write(0xFF);
00265         if(!(response & 0x80)) {
00266             return response;
00267         }
00268     }
00269     _cs = 1;
00270     _spi.write(0xFF);
00271     return -1; // timeout
00272 }
00273 
00274 
00275 int SDFileSystem::_cmd58() {
00276     _cs = 0; 
00277     int arg = 0;
00278     
00279     // send a command
00280     _spi.write(0x40 | 58);
00281     _spi.write(arg >> 24);
00282     _spi.write(arg >> 16);
00283     _spi.write(arg >> 8);
00284     _spi.write(arg >> 0);
00285     _spi.write(0x95);
00286 
00287     // wait for the repsonse (response[7] == 0)
00288     for(int i=0; i<SD_COMMAND_TIMEOUT; i++) {
00289         int response = _spi.write(0xFF);
00290         if(!(response & 0x80)) {
00291             int ocr = _spi.write(0xFF) << 24;
00292             ocr |= _spi.write(0xFF) << 16;
00293             ocr |= _spi.write(0xFF) << 8;
00294             ocr |= _spi.write(0xFF) << 0;
00295 //            printf("OCR = 0x%08X\n", ocr);
00296             _cs = 1;
00297             _spi.write(0xFF);
00298             return response;
00299         }
00300     }
00301     _cs = 1;
00302     _spi.write(0xFF);
00303     return -1; // timeout
00304 }
00305 
00306 int SDFileSystem::_cmd8() {
00307     _cs = 0; 
00308     
00309     // send a command
00310     _spi.write(0x40 | 8); // CMD8
00311     _spi.write(0x00);     // reserved
00312     _spi.write(0x00);     // reserved
00313     _spi.write(0x01);     // 3.3v
00314     _spi.write(0xAA);     // check pattern
00315     _spi.write(0x87);     // crc
00316 
00317     // wait for the repsonse (response[7] == 0)
00318     for(int i=0; i<SD_COMMAND_TIMEOUT * 1000; i++) {
00319         char response[5];
00320         response[0] = _spi.write(0xFF);
00321         if(!(response[0] & 0x80)) {
00322                 for(int j=1; j<5; j++) {
00323                     response[i] = _spi.write(0xFF);
00324                 }
00325                 _cs = 1;
00326                 _spi.write(0xFF);
00327                 return response[0];
00328         }
00329     }
00330     _cs = 1;
00331     _spi.write(0xFF);
00332     return -1; // timeout
00333 }
00334 
00335 int SDFileSystem::_read(char *buffer, int length) {
00336     _cs = 0;
00337 
00338     // read until start byte (0xFF)
00339     while(_spi.write(0xFF) != 0xFE);
00340 
00341     // read data
00342     for(int i=0; i<length; i++) {
00343         buffer[i] = _spi.write(0xFF);
00344     }
00345     _spi.write(0xFF); // checksum
00346     _spi.write(0xFF);
00347 
00348     _cs = 1;    
00349     _spi.write(0xFF);
00350     return 0;
00351 }
00352 
00353 int SDFileSystem::_write(const char *buffer, int length) {
00354     _cs = 0;
00355     
00356     // indicate start of block
00357     _spi.write(0xFE);
00358     
00359     // write the data
00360     for(int i=0; i<length; i++) {
00361         _spi.write(buffer[i]);
00362     }
00363     
00364     // write the checksum
00365     _spi.write(0xFF); 
00366     _spi.write(0xFF);
00367 
00368     // check the repsonse token
00369     if((_spi.write(0xFF) & 0x1F) != 0x05) {
00370         _cs = 1;
00371         _spi.write(0xFF);        
00372         return 1;
00373     }
00374 
00375     // wait for write to finish
00376     while(_spi.write(0xFF) == 0);
00377 
00378     _cs = 1; 
00379     _spi.write(0xFF);
00380     return 0;
00381 }
00382 
00383 static int ext_bits(char *data, int msb, int lsb) {
00384     int bits = 0;
00385     int size = 1 + msb - lsb; 
00386     for(int i=0; i<size; i++) {
00387         int position = lsb + i;
00388         int byte = 15 - (position >> 3);
00389         int bit = position & 0x7;
00390         int value = (data[byte] >> bit) & 1;
00391         bits |= value << i;
00392     }
00393     return bits;
00394 }
00395 
00396 int SDFileSystem::_sd_sectors() {
00397 
00398     // CMD9, Response R2 (R1 byte + 16-byte block read)
00399     if(_cmdx(9, 0) != 0) {
00400         fprintf(stderr, "Didn't get a response from the disk\n");
00401         return 0;
00402     }
00403     
00404     char csd[16];    
00405     if(_read(csd, 16) != 0) {
00406         fprintf(stderr, "Couldn't read csd response from disk\n");
00407         return 0;
00408     }
00409 
00410     // csd_structure : csd[127:126]
00411     // c_size        : csd[73:62]
00412     // c_size_mult   : csd[49:47]
00413     // read_bl_len   : csd[83:80] - the *maximum* read block length
00414 
00415     int csd_structure = ext_bits(csd, 127, 126);
00416     int c_size = ext_bits(csd, 73, 62);
00417     int c_size_mult = ext_bits(csd, 49, 47);
00418     int read_bl_len = ext_bits(csd, 83, 80);
00419 
00420 //    printf("CSD_STRUCT = %d\n", csd_structure);
00421     
00422     if(csd_structure != 0) {
00423         fprintf(stderr, "This disk tastes funny! I only know about type 0 CSD structures\n");
00424         return 0;
00425     }
00426              
00427     // memory capacity = BLOCKNR * BLOCK_LEN
00428     // where
00429     //  BLOCKNR = (C_SIZE+1) * MULT
00430     //  MULT = 2^(C_SIZE_MULT+2) (C_SIZE_MULT < 8)
00431     //  BLOCK_LEN = 2^READ_BL_LEN, (READ_BL_LEN < 12)         
00432                             
00433     int block_len = 1 << read_bl_len;
00434     int mult = 1 << (c_size_mult + 2);
00435     int blocknr = (c_size + 1) * mult;
00436     int capacity = blocknr * block_len;
00437         
00438     int blocks = capacity / 512;
00439         
00440     return blocks;
00441 }