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Rolf Meyer / Mbed 2 deprecated SDServerDemo

A simple demo how to use the HTTPServer with an SDCard file system

SDFileSystem.cpp@0:949146458785, 2009-11-20 (annotated)

Committer:: rolf
Date:: Fri Nov 20 11:25:04 2009 +0000
Revision:: 0:949146458785

Who changed what in which revision?

User	Revision	Line number	New contents of line
rolf	0:949146458785	1	/* mbed Microcontroller Library - SDFileSystem
rolf	0:949146458785	2	* Copyright (c) 2008-2009, sford
rolf	0:949146458785	3	*
rolf	0:949146458785	4	* Introduction
rolf	0:949146458785	5	* ------------
rolf	0:949146458785	6	* SD and MMC cards support a number of interfaces, but common to them all
rolf	0:949146458785	7	* is one based on SPI. This is the one I'm implmenting because it means
rolf	0:949146458785	8	* it is much more portable even though not so performant, and we already
rolf	0:949146458785	9	* have the mbed SPI Interface!
rolf	0:949146458785	10	*
rolf	0:949146458785	11	* The main reference I'm using is Chapter 7, "SPI Mode" of:
rolf	0:949146458785	12	* http://www.sdcard.org/developers/tech/sdcard/pls/Simplified_Physical_Layer_Spec.pdf
rolf	0:949146458785	13	*
rolf	0:949146458785	14	* SPI Startup
rolf	0:949146458785	15	* -----------
rolf	0:949146458785	16	* The SD card powers up in SD mode. The SPI interface mode is selected by
rolf	0:949146458785	17	* asserting CS low and sending the reset command (CMD0). The card will
rolf	0:949146458785	18	* respond with a (R1) response.
rolf	0:949146458785	19	*
rolf	0:949146458785	20	* CMD8 is optionally sent to determine the voltage range supported, and
rolf	0:949146458785	21	* indirectly determine whether it is a version 1.x SD/non-SD card or
rolf	0:949146458785	22	* version 2.x. I'll just ignore this for now.
rolf	0:949146458785	23	*
rolf	0:949146458785	24	* ACMD41 is repeatedly issued to initialise the card, until "in idle"
rolf	0:949146458785	25	* (bit 0) of the R1 response goes to '0', indicating it is initialised.
rolf	0:949146458785	26	*
rolf	0:949146458785	27	* You should also indicate whether the host supports High Capicity cards,
rolf	0:949146458785	28	* and check whether the card is high capacity - i'll also ignore this
rolf	0:949146458785	29	*
rolf	0:949146458785	30	* SPI Protocol
rolf	0:949146458785	31	* ------------
rolf	0:949146458785	32	* The SD SPI protocol is based on transactions made up of 8-bit words, with
rolf	0:949146458785	33	* the host starting every bus transaction by asserting the CS signal low. The
rolf	0:949146458785	34	* card always responds to commands, data blocks and errors.
rolf	0:949146458785	35	*
rolf	0:949146458785	36	* The protocol supports a CRC, but by default it is off (except for the
rolf	0:949146458785	37	* first reset CMD0, where the CRC can just be pre-calculated, and CMD8)
rolf	0:949146458785	38	* I'll leave the CRC off I think!
rolf	0:949146458785	39	*
rolf	0:949146458785	40	* Standard capacity cards have variable data block sizes, whereas High
rolf	0:949146458785	41	* Capacity cards fix the size of data block to 512 bytes. I'll therefore
rolf	0:949146458785	42	* just always use the Standard Capacity cards with a block size of 512 bytes.
rolf	0:949146458785	43	* This is set with CMD16.
rolf	0:949146458785	44	*
rolf	0:949146458785	45	* You can read and write single blocks (CMD17, CMD25) or multiple blocks
rolf	0:949146458785	46	* (CMD18, CMD25). For simplicity, I'll just use single block accesses. When
rolf	0:949146458785	47	* the card gets a read command, it responds with a response token, and then
rolf	0:949146458785	48	* a data token or an error.
rolf	0:949146458785	49	*
rolf	0:949146458785	50	* SPI Command Format
rolf	0:949146458785	51	* ------------------
rolf	0:949146458785	52	* Commands are 6-bytes long, containing the command, 32-bit argument, and CRC.
rolf	0:949146458785	53	*
rolf	0:949146458785	54	* +---------------+------------+------------+-----------+----------+--------------+
rolf	0:949146458785	55	* \| 01 \| cmd[5:0] \| arg[31:24] \| arg[23:16] \| arg[15:8] \| arg[7:0] \| crc[6:0] \| 1 \|
rolf	0:949146458785	56	* +---------------+------------+------------+-----------+----------+--------------+
rolf	0:949146458785	57	*
rolf	0:949146458785	58	* As I'm not using CRC, I can fix that byte to what is needed for CMD0 (0x95)
rolf	0:949146458785	59	*
rolf	0:949146458785	60	* All Application Specific commands shall be preceded with APP_CMD (CMD55).
rolf	0:949146458785	61	*
rolf	0:949146458785	62	* SPI Response Format
rolf	0:949146458785	63	* -------------------
rolf	0:949146458785	64	* The main response format (R1) is a status byte (normally zero). Key flags:
rolf	0:949146458785	65	* idle - 1 if the card is in an idle state/initialising
rolf	0:949146458785	66	* cmd - 1 if an illegal command code was detected
rolf	0:949146458785	67	*
rolf	0:949146458785	68	* +-------------------------------------------------+
rolf	0:949146458785	69	* R1 \| 0 \| arg \| addr \| seq \| crc \| cmd \| erase \| idle \|
rolf	0:949146458785	70	* +-------------------------------------------------+
rolf	0:949146458785	71	*
rolf	0:949146458785	72	* R1b is the same, except it is followed by a busy signal (zeros) until
rolf	0:949146458785	73	* the first non-zero byte when it is ready again.
rolf	0:949146458785	74	*
rolf	0:949146458785	75	* Data Response Token
rolf	0:949146458785	76	* -------------------
rolf	0:949146458785	77	* Every data block written to the card is acknowledged by a byte
rolf	0:949146458785	78	* response token
rolf	0:949146458785	79	*
rolf	0:949146458785	80	* +----------------------+
rolf	0:949146458785	81	* \| xxx \| 0 \| status \| 1 \|
rolf	0:949146458785	82	* +----------------------+
rolf	0:949146458785	83	* 010 - OK!
rolf	0:949146458785	84	* 101 - CRC Error
rolf	0:949146458785	85	* 110 - Write Error
rolf	0:949146458785	86	*
rolf	0:949146458785	87	* Single Block Read and Write
rolf	0:949146458785	88	* ---------------------------
rolf	0:949146458785	89	*
rolf	0:949146458785	90	* Block transfers have a byte header, followed by the data, followed
rolf	0:949146458785	91	* by a 16-bit CRC. In our case, the data will always be 512 bytes.
rolf	0:949146458785	92	*
rolf	0:949146458785	93	* +------+---------+---------+- - - -+---------+-----------+----------+
rolf	0:949146458785	94	* \| 0xFE \| data[0] \| data[1] \| \| data[n] \| crc[15:8] \| crc[7:0] \|
rolf	0:949146458785	95	* +------+---------+---------+- - - -+---------+-----------+----------+
rolf	0:949146458785	96	*/
rolf	0:949146458785	97
rolf	0:949146458785	98	#include "SDFileSystem.h"
rolf	0:949146458785	99
rolf	0:949146458785	100	#define SD_COMMAND_TIMEOUT 5000
rolf	0:949146458785	101
rolf	0:949146458785	102	SDFileSystem::SDFileSystem(PinName mosi, PinName miso, PinName sclk, PinName cs, const char* name) :
rolf	0:949146458785	103	FATFileSystem(name), _spi(mosi, miso, sclk), _cs(cs) {
rolf	0:949146458785	104	_cs = 1;
rolf	0:949146458785	105	}
rolf	0:949146458785	106
rolf	0:949146458785	107	int SDFileSystem::disk_initialize() {
rolf	0:949146458785	108
rolf	0:949146458785	109	_spi.frequency(100000); // Set to 100kHz for initialisation
rolf	0:949146458785	110
rolf	0:949146458785	111	// Initialise the card by clocking it a bit (cs = 1)
rolf	0:949146458785	112	for(int i=0; i<16; i++) {
rolf	0:949146458785	113	_spi.write(0xFF);
rolf	0:949146458785	114	}
rolf	0:949146458785	115
rolf	0:949146458785	116	// send CMD0, should return with all zeros except IDLE STATE set (bit 0)
rolf	0:949146458785	117	if(_cmd(0, 0) != 0x01) {
rolf	0:949146458785	118	fprintf(stderr, "Not in idle state\n");
rolf	0:949146458785	119	return 1;
rolf	0:949146458785	120	}
rolf	0:949146458785	121
rolf	0:949146458785	122	// ACMD41 to give host capacity support (repeat until not busy)
rolf	0:949146458785	123	// ACMD41 is application specific command, so we send APP_CMD (CMD55) beforehand
rolf	0:949146458785	124	for(int i=0;; i++) {
rolf	0:949146458785	125	_cmd(55, 0);
rolf	0:949146458785	126	int response = _cmd(41, 0);
rolf	0:949146458785	127	if(response == 0) {
rolf	0:949146458785	128	break;
rolf	0:949146458785	129	} else if(i > SD_COMMAND_TIMEOUT) {
rolf	0:949146458785	130	fprintf(stderr, "Timeout waiting for card\n");
rolf	0:949146458785	131	return 1;
rolf	0:949146458785	132	}
rolf	0:949146458785	133	}
rolf	0:949146458785	134
rolf	0:949146458785	135	_sectors = _sd_sectors();
rolf	0:949146458785	136
rolf	0:949146458785	137	// Set block length to 512 (CMD16)
rolf	0:949146458785	138	if(_cmd(16, 512) != 0) {
rolf	0:949146458785	139	fprintf(stderr, "Set block timeout\n");
rolf	0:949146458785	140	return 1;
rolf	0:949146458785	141	}
rolf	0:949146458785	142
rolf	0:949146458785	143	_spi.frequency(1000000); // Set to 1MHz for data transfer
rolf	0:949146458785	144	return 0;
rolf	0:949146458785	145	}
rolf	0:949146458785	146
rolf	0:949146458785	147	int SDFileSystem::disk_write(const char *buffer, int block_number) {
rolf	0:949146458785	148	// set write address for single block (CMD24)
rolf	0:949146458785	149	if(_cmd(24, block_number * 512) != 0) {
rolf	0:949146458785	150	return 1;
rolf	0:949146458785	151	}
rolf	0:949146458785	152
rolf	0:949146458785	153	// send the data block
rolf	0:949146458785	154	_write(buffer, 512);
rolf	0:949146458785	155	return 0;
rolf	0:949146458785	156	}
rolf	0:949146458785	157
rolf	0:949146458785	158	int SDFileSystem::disk_read(char *buffer, int block_number) {
rolf	0:949146458785	159	// set read address for single block (CMD17)
rolf	0:949146458785	160	if(_cmd(17, block_number * 512) != 0) {
rolf	0:949146458785	161	return 1;
rolf	0:949146458785	162	}
rolf	0:949146458785	163
rolf	0:949146458785	164	// receive the data
rolf	0:949146458785	165	_read(buffer, 512);
rolf	0:949146458785	166	return 0;
rolf	0:949146458785	167	}
rolf	0:949146458785	168
rolf	0:949146458785	169	int SDFileSystem::disk_status() { return 0; }
rolf	0:949146458785	170	int SDFileSystem::disk_sync() { return 0; }
rolf	0:949146458785	171	int SDFileSystem::disk_sectors() { return _sectors; }
rolf	0:949146458785	172
rolf	0:949146458785	173	// PRIVATE FUNCTIONS
rolf	0:949146458785	174
rolf	0:949146458785	175	int SDFileSystem::_cmd(int cmd, int arg) {
rolf	0:949146458785	176	_cs = 0;
rolf	0:949146458785	177
rolf	0:949146458785	178	// send a command
rolf	0:949146458785	179	_spi.write(0x40 \| cmd);
rolf	0:949146458785	180	_spi.write(arg >> 24);
rolf	0:949146458785	181	_spi.write(arg >> 16);
rolf	0:949146458785	182	_spi.write(arg >> 8);
rolf	0:949146458785	183	_spi.write(arg >> 0);
rolf	0:949146458785	184	_spi.write(0x95);
rolf	0:949146458785	185
rolf	0:949146458785	186	// wait for the repsonse (response[7] == 0)
rolf	0:949146458785	187	for(int i=0; i<SD_COMMAND_TIMEOUT; i++) {
rolf	0:949146458785	188	int response = _spi.write(0xFF);
rolf	0:949146458785	189	if(!(response & 0x80)) {
rolf	0:949146458785	190	_cs = 1;
rolf	0:949146458785	191	return response;
rolf	0:949146458785	192	}
rolf	0:949146458785	193	}
rolf	0:949146458785	194	_cs = 1;
rolf	0:949146458785	195	return -1; // timeout
rolf	0:949146458785	196	}
rolf	0:949146458785	197
rolf	0:949146458785	198	int SDFileSystem::_read(char *buffer, int length) {
rolf	0:949146458785	199	_cs = 0;
rolf	0:949146458785	200
rolf	0:949146458785	201	// read until start byte (0xFF)
rolf	0:949146458785	202	while(_spi.write(0xFF) != 0xFE);
rolf	0:949146458785	203
rolf	0:949146458785	204	// read data
rolf	0:949146458785	205	for(int i=0; i<length; i++) {
rolf	0:949146458785	206	buffer[i] = _spi.write(0xFF);
rolf	0:949146458785	207	}
rolf	0:949146458785	208	_spi.write(0xFF); // checksum
rolf	0:949146458785	209	_spi.write(0xFF);
rolf	0:949146458785	210
rolf	0:949146458785	211	_cs = 1;
rolf	0:949146458785	212	return 0;
rolf	0:949146458785	213	}
rolf	0:949146458785	214
rolf	0:949146458785	215	int SDFileSystem::_write(const char *buffer, int length) {
rolf	0:949146458785	216	_cs = 0;
rolf	0:949146458785	217
rolf	0:949146458785	218	// indicate start of block
rolf	0:949146458785	219	_spi.write(0xFE);
rolf	0:949146458785	220
rolf	0:949146458785	221	// write the data
rolf	0:949146458785	222	for(int i=0; i<length; i++) {
rolf	0:949146458785	223	_spi.write(buffer[i]);
rolf	0:949146458785	224	}
rolf	0:949146458785	225
rolf	0:949146458785	226	// write the checksum
rolf	0:949146458785	227	_spi.write(0xFF);
rolf	0:949146458785	228	_spi.write(0xFF);
rolf	0:949146458785	229
rolf	0:949146458785	230	// check the repsonse token
rolf	0:949146458785	231	if((_spi.write(0xFF) & 0x1F) != 0x05) {
rolf	0:949146458785	232	_cs = 1;
rolf	0:949146458785	233	return 1;
rolf	0:949146458785	234	}
rolf	0:949146458785	235
rolf	0:949146458785	236	// wait for write to finish
rolf	0:949146458785	237	while(_spi.write(0xFF) == 0);
rolf	0:949146458785	238
rolf	0:949146458785	239	_cs = 1;
rolf	0:949146458785	240	return 0;
rolf	0:949146458785	241	}
rolf	0:949146458785	242
rolf	0:949146458785	243	static int ext_bits(char *data, int msb, int lsb) {
rolf	0:949146458785	244	int bits = 0;
rolf	0:949146458785	245	int size = 1 + msb - lsb;
rolf	0:949146458785	246	for(int i=0; i<size; i++) {
rolf	0:949146458785	247	int position = lsb + i;
rolf	0:949146458785	248	int byte = 15 - (position >> 3);
rolf	0:949146458785	249	int bit = position & 0x7;
rolf	0:949146458785	250	int value = (data[byte] >> bit) & 1;
rolf	0:949146458785	251	bits \|= value << i;
rolf	0:949146458785	252	}
rolf	0:949146458785	253	return bits;
rolf	0:949146458785	254	}
rolf	0:949146458785	255
rolf	0:949146458785	256	int SDFileSystem::_sd_sectors() {
rolf	0:949146458785	257
rolf	0:949146458785	258	// CMD9, Response R2 (R1 byte + 16-byte block read)
rolf	0:949146458785	259	if(_cmd(9, 0) != 0) {
rolf	0:949146458785	260	fprintf(stderr, "Didn't get a response from the disk\n");
rolf	0:949146458785	261	return 0;
rolf	0:949146458785	262	}
rolf	0:949146458785	263
rolf	0:949146458785	264	char csd[16];
rolf	0:949146458785	265	if(_read(csd, 16) != 0) {
rolf	0:949146458785	266	fprintf(stderr, "Couldn't read csd response from disk\n");
rolf	0:949146458785	267	return 0;
rolf	0:949146458785	268	}
rolf	0:949146458785	269
rolf	0:949146458785	270	// csd_structure : csd[127:126]
rolf	0:949146458785	271	// c_size : csd[73:62]
rolf	0:949146458785	272	// c_size_mult : csd[49:47]
rolf	0:949146458785	273	// read_bl_len : csd[83:80]
rolf	0:949146458785	274
rolf	0:949146458785	275	int csd_structure = ext_bits(csd, 127, 126);
rolf	0:949146458785	276	int c_size = ext_bits(csd, 73, 62);
rolf	0:949146458785	277	int c_size_mult = ext_bits(csd, 49, 47);
rolf	0:949146458785	278	int read_bl_len = ext_bits(csd, 83, 80);
rolf	0:949146458785	279
rolf	0:949146458785	280	if(csd_structure != 0) {
rolf	0:949146458785	281	fprintf(stderr, "This disk tastes funny! I only know about type 0 CSD structures");
rolf	0:949146458785	282	return 0;
rolf	0:949146458785	283	}
rolf	0:949146458785	284
rolf	0:949146458785	285	int blocks = (c_size + 1) * (1 << (c_size_mult + 2));
rolf	0:949146458785	286	int block_size = 1 << read_bl_len;
rolf	0:949146458785	287
rolf	0:949146458785	288	if(block_size != 512) {
rolf	0:949146458785	289	fprintf(stderr, "This disk tastes funny! I only like 512-byte blocks");
rolf	0:949146458785	290	return 0;
rolf	0:949146458785	291	}
rolf	0:949146458785	292
rolf	0:949146458785	293	return blocks;
rolf	0:949146458785	294	}

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Type:	Program
Mbed OS support:	Mbed 2 deprecated
Created:	20 Nov 2009
Imports:	28
Forks:	0
Commits:	1
Dependents:	0
Dependencies:	2
Followers:	2

SDFileSystem.cpp@0:949146458785, 2009-11-20 (annotated)

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