Samuel Mokrani / Mbed 2 deprecated USBMSD_SD_HelloWorld_Mbed

USBMSD SD card Hello World for Mbed platforms

Dependencies:   mbed USBMSD_SD USBDevice

SDcard.cpp@2:27a7e7f8d399, 2011-11-11 (annotated)

Committer:
samux
Date:
Fri Nov 11 15:22:53 2011 +0000
Revision:
2:27a7e7f8d399
we have 2MB with the sdcard!!

Who changed what in which revision?

UserRevisionLine numberNew contents of line
samux 2:27a7e7f8d399 1 /* mbed Microcontroller Library - SDFileSystem
samux 2:27a7e7f8d399 2 * Copyright (c) 2008-2009, sford
samux 2:27a7e7f8d399 3 *
samux 2:27a7e7f8d399 4 * Introduction
samux 2:27a7e7f8d399 5 * ------------
samux 2:27a7e7f8d399 6 * SD and MMC cards support a number of interfaces, but common to them all
samux 2:27a7e7f8d399 7 * is one based on SPI. This is the one I'm implmenting because it means
samux 2:27a7e7f8d399 8 * it is much more portable even though not so performant, and we already
samux 2:27a7e7f8d399 9 * have the mbed SPI Interface!
samux 2:27a7e7f8d399 10 *
samux 2:27a7e7f8d399 11 * The main reference I'm using is Chapter 7, "SPI Mode" of:
samux 2:27a7e7f8d399 12 * http://www.sdcard.org/developers/tech/sdcard/pls/Simplified_Physical_Layer_Spec.pdf
samux 2:27a7e7f8d399 13 *
samux 2:27a7e7f8d399 14 * SPI Startup
samux 2:27a7e7f8d399 15 * -----------
samux 2:27a7e7f8d399 16 * The SD card powers up in SD mode. The SPI interface mode is selected by
samux 2:27a7e7f8d399 17 * asserting CS low and sending the reset command (CMD0). The card will
samux 2:27a7e7f8d399 18 * respond with a (R1) response.
samux 2:27a7e7f8d399 19 *
samux 2:27a7e7f8d399 20 * CMD8 is optionally sent to determine the voltage range supported, and
samux 2:27a7e7f8d399 21 * indirectly determine whether it is a version 1.x SD/non-SD card or
samux 2:27a7e7f8d399 22 * version 2.x. I'll just ignore this for now.
samux 2:27a7e7f8d399 23 *
samux 2:27a7e7f8d399 24 * ACMD41 is repeatedly issued to initialise the card, until "in idle"
samux 2:27a7e7f8d399 25 * (bit 0) of the R1 response goes to '0', indicating it is initialised.
samux 2:27a7e7f8d399 26 *
samux 2:27a7e7f8d399 27 * You should also indicate whether the host supports High Capicity cards,
samux 2:27a7e7f8d399 28 * and check whether the card is high capacity - i'll also ignore this
samux 2:27a7e7f8d399 29 *
samux 2:27a7e7f8d399 30 * SPI Protocol
samux 2:27a7e7f8d399 31 * ------------
samux 2:27a7e7f8d399 32 * The SD SPI protocol is based on transactions made up of 8-bit words, with
samux 2:27a7e7f8d399 33 * the host starting every bus transaction by asserting the CS signal low. The
samux 2:27a7e7f8d399 34 * card always responds to commands, data blocks and errors.
samux 2:27a7e7f8d399 35 *
samux 2:27a7e7f8d399 36 * The protocol supports a CRC, but by default it is off (except for the
samux 2:27a7e7f8d399 37 * first reset CMD0, where the CRC can just be pre-calculated, and CMD8)
samux 2:27a7e7f8d399 38 * I'll leave the CRC off I think!
samux 2:27a7e7f8d399 39 *
samux 2:27a7e7f8d399 40 * Standard capacity cards have variable data block sizes, whereas High
samux 2:27a7e7f8d399 41 * Capacity cards fix the size of data block to 512 bytes. I'll therefore
samux 2:27a7e7f8d399 42 * just always use the Standard Capacity cards with a block size of 512 bytes.
samux 2:27a7e7f8d399 43 * This is set with CMD16.
samux 2:27a7e7f8d399 44 *
samux 2:27a7e7f8d399 45 * You can read and write single blocks (CMD17, CMD25) or multiple blocks
samux 2:27a7e7f8d399 46 * (CMD18, CMD25). For simplicity, I'll just use single block accesses. When
samux 2:27a7e7f8d399 47 * the card gets a read command, it responds with a response token, and then
samux 2:27a7e7f8d399 48 * a data token or an error.
samux 2:27a7e7f8d399 49 *
samux 2:27a7e7f8d399 50 * SPI Command Format
samux 2:27a7e7f8d399 51 * ------------------
samux 2:27a7e7f8d399 52 * Commands are 6-bytes long, containing the command, 32-bit argument, and CRC.
samux 2:27a7e7f8d399 53 *
samux 2:27a7e7f8d399 54 * +---------------+------------+------------+-----------+----------+--------------+
samux 2:27a7e7f8d399 55 * | 01 | cmd[5:0] | arg[31:24] | arg[23:16] | arg[15:8] | arg[7:0] | crc[6:0] | 1 |
samux 2:27a7e7f8d399 56 * +---------------+------------+------------+-----------+----------+--------------+
samux 2:27a7e7f8d399 57 *
samux 2:27a7e7f8d399 58 * As I'm not using CRC, I can fix that byte to what is needed for CMD0 (0x95)
samux 2:27a7e7f8d399 59 *
samux 2:27a7e7f8d399 60 * All Application Specific commands shall be preceded with APP_CMD (CMD55).
samux 2:27a7e7f8d399 61 *
samux 2:27a7e7f8d399 62 * SPI Response Format
samux 2:27a7e7f8d399 63 * -------------------
samux 2:27a7e7f8d399 64 * The main response format (R1) is a status byte (normally zero). Key flags:
samux 2:27a7e7f8d399 65 * idle - 1 if the card is in an idle state/initialising
samux 2:27a7e7f8d399 66 * cmd - 1 if an illegal command code was detected
samux 2:27a7e7f8d399 67 *
samux 2:27a7e7f8d399 68 * +-------------------------------------------------+
samux 2:27a7e7f8d399 69 * R1 | 0 | arg | addr | seq | crc | cmd | erase | idle |
samux 2:27a7e7f8d399 70 * +-------------------------------------------------+
samux 2:27a7e7f8d399 71 *
samux 2:27a7e7f8d399 72 * R1b is the same, except it is followed by a busy signal (zeros) until
samux 2:27a7e7f8d399 73 * the first non-zero byte when it is ready again.
samux 2:27a7e7f8d399 74 *
samux 2:27a7e7f8d399 75 * Data Response Token
samux 2:27a7e7f8d399 76 * -------------------
samux 2:27a7e7f8d399 77 * Every data block written to the card is acknowledged by a byte
samux 2:27a7e7f8d399 78 * response token
samux 2:27a7e7f8d399 79 *
samux 2:27a7e7f8d399 80 * +----------------------+
samux 2:27a7e7f8d399 81 * | xxx | 0 | status | 1 |
samux 2:27a7e7f8d399 82 * +----------------------+
samux 2:27a7e7f8d399 83 * 010 - OK!
samux 2:27a7e7f8d399 84 * 101 - CRC Error
samux 2:27a7e7f8d399 85 * 110 - Write Error
samux 2:27a7e7f8d399 86 *
samux 2:27a7e7f8d399 87 * Single Block Read and Write
samux 2:27a7e7f8d399 88 * ---------------------------
samux 2:27a7e7f8d399 89 *
samux 2:27a7e7f8d399 90 * Block transfers have a byte header, followed by the data, followed
samux 2:27a7e7f8d399 91 * by a 16-bit CRC. In our case, the data will always be 512 bytes.
samux 2:27a7e7f8d399 92 *
samux 2:27a7e7f8d399 93 * +------+---------+---------+- - - -+---------+-----------+----------+
samux 2:27a7e7f8d399 94 * | 0xFE | data[0] | data[1] | | data[n] | crc[15:8] | crc[7:0] |
samux 2:27a7e7f8d399 95 * +------+---------+---------+- - - -+---------+-----------+----------+
samux 2:27a7e7f8d399 96 */
samux 2:27a7e7f8d399 97
samux 2:27a7e7f8d399 98 #include "SDcard.h"
samux 2:27a7e7f8d399 99
samux 2:27a7e7f8d399 100 #define SD_COMMAND_TIMEOUT 5000
samux 2:27a7e7f8d399 101
samux 2:27a7e7f8d399 102 SDcard::SDcard(PinName mosi, PinName miso, PinName sclk, PinName cs) :
samux 2:27a7e7f8d399 103 _spi(mosi, miso, sclk), _cs(cs) {
samux 2:27a7e7f8d399 104 _cs = 1;
samux 2:27a7e7f8d399 105 }
samux 2:27a7e7f8d399 106
samux 2:27a7e7f8d399 107 int SDcard::disk_write(const char *buffer, int block_number) {
samux 2:27a7e7f8d399 108 // set write address for single block (CMD24)
samux 2:27a7e7f8d399 109 if(_cmd(24, block_number * 512) != 0) {
samux 2:27a7e7f8d399 110 return 1;
samux 2:27a7e7f8d399 111 }
samux 2:27a7e7f8d399 112
samux 2:27a7e7f8d399 113 // send the data block
samux 2:27a7e7f8d399 114 _write(buffer, 512);
samux 2:27a7e7f8d399 115 return 0;
samux 2:27a7e7f8d399 116 }
samux 2:27a7e7f8d399 117
samux 2:27a7e7f8d399 118 int SDcard::disk_read(char *buffer, int block_number) {
samux 2:27a7e7f8d399 119 // set read address for single block (CMD17)
samux 2:27a7e7f8d399 120 if(_cmd(17, block_number * 512) != 0) {
samux 2:27a7e7f8d399 121 return 1;
samux 2:27a7e7f8d399 122 }
samux 2:27a7e7f8d399 123
samux 2:27a7e7f8d399 124 // receive the data
samux 2:27a7e7f8d399 125 _read(buffer, 512);
samux 2:27a7e7f8d399 126 return 0;
samux 2:27a7e7f8d399 127 }
samux 2:27a7e7f8d399 128
samux 2:27a7e7f8d399 129 // PRIVATE FUNCTIONS
samux 2:27a7e7f8d399 130
samux 2:27a7e7f8d399 131 int SDcard::_cmd(int cmd, int arg) {
samux 2:27a7e7f8d399 132 _cs = 0;
samux 2:27a7e7f8d399 133
samux 2:27a7e7f8d399 134 // send a command
samux 2:27a7e7f8d399 135 _spi.write(0x40 | cmd);
samux 2:27a7e7f8d399 136 _spi.write(arg >> 24);
samux 2:27a7e7f8d399 137 _spi.write(arg >> 16);
samux 2:27a7e7f8d399 138 _spi.write(arg >> 8);
samux 2:27a7e7f8d399 139 _spi.write(arg >> 0);
samux 2:27a7e7f8d399 140 _spi.write(0x95);
samux 2:27a7e7f8d399 141
samux 2:27a7e7f8d399 142 // wait for the repsonse (response[7] == 0)
samux 2:27a7e7f8d399 143 for(int i=0; i<SD_COMMAND_TIMEOUT; i++) {
samux 2:27a7e7f8d399 144 int response = _spi.write(0xFF);
samux 2:27a7e7f8d399 145 if(!(response & 0x80)) {
samux 2:27a7e7f8d399 146 _cs = 1;
samux 2:27a7e7f8d399 147 return response;
samux 2:27a7e7f8d399 148 }
samux 2:27a7e7f8d399 149 }
samux 2:27a7e7f8d399 150 _cs = 1;
samux 2:27a7e7f8d399 151 return -1; // timeout
samux 2:27a7e7f8d399 152 }
samux 2:27a7e7f8d399 153
samux 2:27a7e7f8d399 154 int SDcard::_read(char *buffer, int length) {
samux 2:27a7e7f8d399 155 _cs = 0;
samux 2:27a7e7f8d399 156
samux 2:27a7e7f8d399 157 // read until start byte (0xFF)
samux 2:27a7e7f8d399 158 while(_spi.write(0xFF) != 0xFE);
samux 2:27a7e7f8d399 159
samux 2:27a7e7f8d399 160 // read data
samux 2:27a7e7f8d399 161 for(int i=0; i<length; i++) {
samux 2:27a7e7f8d399 162 buffer[i] = _spi.write(0xFF);
samux 2:27a7e7f8d399 163 }
samux 2:27a7e7f8d399 164 _spi.write(0xFF); // checksum
samux 2:27a7e7f8d399 165 _spi.write(0xFF);
samux 2:27a7e7f8d399 166
samux 2:27a7e7f8d399 167 _cs = 1;
samux 2:27a7e7f8d399 168 return 0;
samux 2:27a7e7f8d399 169 }
samux 2:27a7e7f8d399 170
samux 2:27a7e7f8d399 171 int SDcard::_write(const char *buffer, int length) {
samux 2:27a7e7f8d399 172 _cs = 0;
samux 2:27a7e7f8d399 173
samux 2:27a7e7f8d399 174 // indicate start of block
samux 2:27a7e7f8d399 175 _spi.write(0xFE);
samux 2:27a7e7f8d399 176
samux 2:27a7e7f8d399 177 // write the data
samux 2:27a7e7f8d399 178 for(int i=0; i<length; i++) {
samux 2:27a7e7f8d399 179 _spi.write(buffer[i]);
samux 2:27a7e7f8d399 180 }
samux 2:27a7e7f8d399 181
samux 2:27a7e7f8d399 182 // write the checksum
samux 2:27a7e7f8d399 183 _spi.write(0xFF);
samux 2:27a7e7f8d399 184 _spi.write(0xFF);
samux 2:27a7e7f8d399 185
samux 2:27a7e7f8d399 186 // check the repsonse token
samux 2:27a7e7f8d399 187 if((_spi.write(0xFF) & 0x1F) != 0x05) {
samux 2:27a7e7f8d399 188 _cs = 1;
samux 2:27a7e7f8d399 189 return 1;
samux 2:27a7e7f8d399 190 }
samux 2:27a7e7f8d399 191
samux 2:27a7e7f8d399 192 // wait for write to finish
samux 2:27a7e7f8d399 193 while(_spi.write(0xFF) == 0);
samux 2:27a7e7f8d399 194
samux 2:27a7e7f8d399 195 _cs = 1;
samux 2:27a7e7f8d399 196 return 0;
samux 2:27a7e7f8d399 197 }