Diff: USB_SDcard.cpp

Revision:

4:980e6470dcce

Parent:

3:0ffb2eee9e06

Child:

5:8afbc15d6892

--- a/USB_SDcard.cpp	Fri Nov 11 16:12:21 2011 +0000
+++ /dev/null	Thu Jan 01 00:00:00 1970 +0000
@@ -1,197 +0,0 @@
-/* mbed Microcontroller Library - SDFileSystem
- * Copyright (c) 2008-2009, sford
- *
- * Introduction
- * ------------
- * SD and MMC cards support a number of interfaces, but common to them all
- * is one based on SPI. This is the one I'm implmenting because it means
- * it is much more portable even though not so performant, and we already 
- * have the mbed SPI Interface!
- *
- * The main reference I'm using is Chapter 7, "SPI Mode" of: 
- *  http://www.sdcard.org/developers/tech/sdcard/pls/Simplified_Physical_Layer_Spec.pdf
- *
- * SPI Startup
- * -----------
- * The SD card powers up in SD mode. The SPI interface mode is selected by
- * asserting CS low and sending the reset command (CMD0). The card will 
- * respond with a (R1) response.
- *
- * CMD8 is optionally sent to determine the voltage range supported, and 
- * indirectly determine whether it is a version 1.x SD/non-SD card or 
- * version 2.x. I'll just ignore this for now.
- *
- * ACMD41 is repeatedly issued to initialise the card, until "in idle"
- * (bit 0) of the R1 response goes to '0', indicating it is initialised.
- *
- * You should also indicate whether the host supports High Capicity cards,
- * and check whether the card is high capacity - i'll also ignore this
- *
- * SPI Protocol
- * ------------
- * The SD SPI protocol is based on transactions made up of 8-bit words, with
- * the host starting every bus transaction by asserting the CS signal low. The
- * card always responds to commands, data blocks and errors.
- * 
- * The protocol supports a CRC, but by default it is off (except for the 
- * first reset CMD0, where the CRC can just be pre-calculated, and CMD8)
- * I'll leave the CRC off I think! 
- * 
- * Standard capacity cards have variable data block sizes, whereas High 
- * Capacity cards fix the size of data block to 512 bytes. I'll therefore
- * just always use the Standard Capacity cards with a block size of 512 bytes.
- * This is set with CMD16.
- *
- * You can read and write single blocks (CMD17, CMD25) or multiple blocks 
- * (CMD18, CMD25). For simplicity, I'll just use single block accesses. When
- * the card gets a read command, it responds with a response token, and then 
- * a data token or an error.
- * 
- * SPI Command Format
- * ------------------
- * Commands are 6-bytes long, containing the command, 32-bit argument, and CRC.
- *
- * +---------------+------------+------------+-----------+----------+--------------+
- * | 01 | cmd[5:0] | arg[31:24] | arg[23:16] | arg[15:8] | arg[7:0] | crc[6:0] | 1 |
- * +---------------+------------+------------+-----------+----------+--------------+
- *
- * As I'm not using CRC, I can fix that byte to what is needed for CMD0 (0x95)
- *
- * All Application Specific commands shall be preceded with APP_CMD (CMD55).
- *
- * SPI Response Format
- * -------------------
- * The main response format (R1) is a status byte (normally zero). Key flags:
- *  idle - 1 if the card is in an idle state/initialising 
- *  cmd  - 1 if an illegal command code was detected
- *
- *    +-------------------------------------------------+
- * R1 | 0 | arg | addr | seq | crc | cmd | erase | idle |
- *    +-------------------------------------------------+
- *
- * R1b is the same, except it is followed by a busy signal (zeros) until
- * the first non-zero byte when it is ready again.
- *
- * Data Response Token
- * -------------------
- * Every data block written to the card is acknowledged by a byte 
- * response token
- *
- * +----------------------+
- * | xxx | 0 | status | 1 |
- * +----------------------+
- *              010 - OK!
- *              101 - CRC Error
- *              110 - Write Error
- *
- * Single Block Read and Write
- * ---------------------------
- *
- * Block transfers have a byte header, followed by the data, followed
- * by a 16-bit CRC. In our case, the data will always be 512 bytes.
- *  
- * +------+---------+---------+- -  - -+---------+-----------+----------+
- * | 0xFE | data[0] | data[1] |        | data[n] | crc[15:8] | crc[7:0] | 
- * +------+---------+---------+- -  - -+---------+-----------+----------+
- */
- 
-#include "USB_SDcard.h"
-
-#define SD_COMMAND_TIMEOUT 5000
-
-USB_SDcard::USB_SDcard(PinName mosi, PinName miso, PinName sclk, PinName cs) :
-  _spi(mosi, miso, sclk), _cs(cs) {
-      _cs = 1; 
-}
-
-int USB_SDcard::blockWrite(uint8_t * buffer, uint16_t block_number) {
-    // set write address for single block (CMD24)
-    if(_cmd(24, block_number * 512) != 0) {
-        return 1;
-    }
-
-    // send the data block
-    _write(buffer, 512);    
-    return 0;    
-}
-
-int USB_SDcard::blockRead(uint8_t * buffer, uint16_t block_number) {        
-    // set read address for single block (CMD17)
-    if(_cmd(17, block_number * 512) != 0) {
-        return 1;
-    }
-    
-    // receive the data
-    _read(buffer, 512);
-    return 0;
-}
-
-// PRIVATE FUNCTIONS
-
-int USB_SDcard::_cmd(int cmd, int arg) {
-    _cs = 0; 
-
-    // send a command
-    _spi.write(0x40 | cmd);
-    _spi.write(arg >> 24);
-    _spi.write(arg >> 16);
-    _spi.write(arg >> 8);
-    _spi.write(arg >> 0);
-    _spi.write(0x95);
-
-    // wait for the repsonse (response[7] == 0)
-    for(int i=0; i<SD_COMMAND_TIMEOUT; i++) {
-        int response = _spi.write(0xFF);
-        if(!(response & 0x80)) {
-            _cs = 1;
-            return response;
-        }
-    }
-    _cs = 1;
-    return -1; // timeout
-}
-
-int USB_SDcard::_read(uint8_t * buffer, uint16_t length) {
-    _cs = 0;
-
-    // read until start byte (0xFF)
-    while(_spi.write(0xFF) != 0xFE);
-
-    // read data
-    for(int i=0; i<length; i++) {
-        buffer[i] = _spi.write(0xFF);
-    }
-    _spi.write(0xFF); // checksum
-    _spi.write(0xFF);
-
-    _cs = 1;    
-    return 0;
-}
-
-int USB_SDcard::_write(uint8_t * buffer, uint16_t length) {
-    _cs = 0;
-    
-    // indicate start of block
-    _spi.write(0xFE);
-    
-    // write the data
-    for(int i=0; i<length; i++) {
-        _spi.write(buffer[i]);
-    }
-    
-    // write the checksum
-    _spi.write(0xFF); 
-    _spi.write(0xFF);
-
-    // check the repsonse token
-    if((_spi.write(0xFF) & 0x1F) != 0x05) {
-        _cs = 1; 
-        return 1;
-    }
-
-    // wait for write to finish
-    while(_spi.write(0xFF) == 0);
-
-    _cs = 1; 
-    return 0;
-}