Rolf Meyer
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SDServerDemo
A simple demo how to use the HTTPServer with an SDCard file system
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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 SDFileSystem::SDFileSystem(PinName mosi, PinName miso, PinName sclk, PinName cs, const char* name) : 00103 FATFileSystem(name), _spi(mosi, miso, sclk), _cs(cs) { 00104 _cs = 1; 00105 } 00106 00107 int SDFileSystem::disk_initialize() { 00108 00109 _spi.frequency(100000); // Set to 100kHz for initialisation 00110 00111 // Initialise the card by clocking it a bit (cs = 1) 00112 for(int i=0; i<16; i++) { 00113 _spi.write(0xFF); 00114 } 00115 00116 // send CMD0, should return with all zeros except IDLE STATE set (bit 0) 00117 if(_cmd(0, 0) != 0x01) { 00118 fprintf(stderr, "Not in idle state\n"); 00119 return 1; 00120 } 00121 00122 // ACMD41 to give host capacity support (repeat until not busy) 00123 // ACMD41 is application specific command, so we send APP_CMD (CMD55) beforehand 00124 for(int i=0;; i++) { 00125 _cmd(55, 0); 00126 int response = _cmd(41, 0); 00127 if(response == 0) { 00128 break; 00129 } else if(i > SD_COMMAND_TIMEOUT) { 00130 fprintf(stderr, "Timeout waiting for card\n"); 00131 return 1; 00132 } 00133 } 00134 00135 _sectors = _sd_sectors(); 00136 00137 // Set block length to 512 (CMD16) 00138 if(_cmd(16, 512) != 0) { 00139 fprintf(stderr, "Set block timeout\n"); 00140 return 1; 00141 } 00142 00143 _spi.frequency(1000000); // Set to 1MHz for data transfer 00144 return 0; 00145 } 00146 00147 int SDFileSystem::disk_write(const char *buffer, int block_number) { 00148 // set write address for single block (CMD24) 00149 if(_cmd(24, block_number * 512) != 0) { 00150 return 1; 00151 } 00152 00153 // send the data block 00154 _write(buffer, 512); 00155 return 0; 00156 } 00157 00158 int SDFileSystem::disk_read(char *buffer, int block_number) { 00159 // set read address for single block (CMD17) 00160 if(_cmd(17, block_number * 512) != 0) { 00161 return 1; 00162 } 00163 00164 // receive the data 00165 _read(buffer, 512); 00166 return 0; 00167 } 00168 00169 int SDFileSystem::disk_status() { return 0; } 00170 int SDFileSystem::disk_sync() { return 0; } 00171 int SDFileSystem::disk_sectors() { return _sectors; } 00172 00173 // PRIVATE FUNCTIONS 00174 00175 int SDFileSystem::_cmd(int cmd, int arg) { 00176 _cs = 0; 00177 00178 // send a command 00179 _spi.write(0x40 | cmd); 00180 _spi.write(arg >> 24); 00181 _spi.write(arg >> 16); 00182 _spi.write(arg >> 8); 00183 _spi.write(arg >> 0); 00184 _spi.write(0x95); 00185 00186 // wait for the repsonse (response[7] == 0) 00187 for(int i=0; i<SD_COMMAND_TIMEOUT; i++) { 00188 int response = _spi.write(0xFF); 00189 if(!(response & 0x80)) { 00190 _cs = 1; 00191 return response; 00192 } 00193 } 00194 _cs = 1; 00195 return -1; // timeout 00196 } 00197 00198 int SDFileSystem::_read(char *buffer, int length) { 00199 _cs = 0; 00200 00201 // read until start byte (0xFF) 00202 while(_spi.write(0xFF) != 0xFE); 00203 00204 // read data 00205 for(int i=0; i<length; i++) { 00206 buffer[i] = _spi.write(0xFF); 00207 } 00208 _spi.write(0xFF); // checksum 00209 _spi.write(0xFF); 00210 00211 _cs = 1; 00212 return 0; 00213 } 00214 00215 int SDFileSystem::_write(const char *buffer, int length) { 00216 _cs = 0; 00217 00218 // indicate start of block 00219 _spi.write(0xFE); 00220 00221 // write the data 00222 for(int i=0; i<length; i++) { 00223 _spi.write(buffer[i]); 00224 } 00225 00226 // write the checksum 00227 _spi.write(0xFF); 00228 _spi.write(0xFF); 00229 00230 // check the repsonse token 00231 if((_spi.write(0xFF) & 0x1F) != 0x05) { 00232 _cs = 1; 00233 return 1; 00234 } 00235 00236 // wait for write to finish 00237 while(_spi.write(0xFF) == 0); 00238 00239 _cs = 1; 00240 return 0; 00241 } 00242 00243 static int ext_bits(char *data, int msb, int lsb) { 00244 int bits = 0; 00245 int size = 1 + msb - lsb; 00246 for(int i=0; i<size; i++) { 00247 int position = lsb + i; 00248 int byte = 15 - (position >> 3); 00249 int bit = position & 0x7; 00250 int value = (data[byte] >> bit) & 1; 00251 bits |= value << i; 00252 } 00253 return bits; 00254 } 00255 00256 int SDFileSystem::_sd_sectors() { 00257 00258 // CMD9, Response R2 (R1 byte + 16-byte block read) 00259 if(_cmd(9, 0) != 0) { 00260 fprintf(stderr, "Didn't get a response from the disk\n"); 00261 return 0; 00262 } 00263 00264 char csd[16]; 00265 if(_read(csd, 16) != 0) { 00266 fprintf(stderr, "Couldn't read csd response from disk\n"); 00267 return 0; 00268 } 00269 00270 // csd_structure : csd[127:126] 00271 // c_size : csd[73:62] 00272 // c_size_mult : csd[49:47] 00273 // read_bl_len : csd[83:80] 00274 00275 int csd_structure = ext_bits(csd, 127, 126); 00276 int c_size = ext_bits(csd, 73, 62); 00277 int c_size_mult = ext_bits(csd, 49, 47); 00278 int read_bl_len = ext_bits(csd, 83, 80); 00279 00280 if(csd_structure != 0) { 00281 fprintf(stderr, "This disk tastes funny! I only know about type 0 CSD structures"); 00282 return 0; 00283 } 00284 00285 int blocks = (c_size + 1) * (1 << (c_size_mult + 2)); 00286 int block_size = 1 << read_bl_len; 00287 00288 if(block_size != 512) { 00289 fprintf(stderr, "This disk tastes funny! I only like 512-byte blocks"); 00290 return 0; 00291 } 00292 00293 return blocks; 00294 }
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