sdcard.c

加速度采集器。基于ATMega16L.AVRSTUIDIO4

#include "SDCard.h"

unsigned char sdBuffer[512];

unsigned char SPITransfer(unsigned char data)
{
	/* 启动数据传输 */
	SPDR = data;
	/* 等待传输结束 */
	while(!(SPSR & (1<<SPIF)));
	// Fetch data
	return SPDR;
}

unsigned char sdSendCommand(unsigned char index, unsigned long argument)
{
	unsigned char result;
	unsigned char cntNcr = 0;


	//Transmit Command
	//1. Transmit index
	SPITransfer(index|0x40);
	//2. Transimit argument
	SPITransfer( *((unsigned char*)&argument+3) );
	SPITransfer( *((unsigned char*)&argument+2) );
	SPITransfer( *((unsigned char*)&argument+1) );
	SPITransfer( *((unsigned char*)&argument+0) );
	//3.Transimit CRC
	if(!index)	//CMD0
		SPITransfer(0x95);
	else
		SPITransfer(0xff);	//has 1 end bit

	//Transimit Ncr H to wait for 1 byte Response
	do
	{
		result = SPITransfer(0xff);
		if(cntNcr++>8)
			return 0xff;		//No Card
	}while(result&0x80);		//the MSB = 1;

	return result;
}

unsigned char sdReceiveDataBlock(unsigned short length, unsigned short timeout)
{
	unsigned char  result;
	unsigned short cnt = 0;
	//Transimit Ncr H to wait for StartBlock=0xFE
	do
	{
		result = SPITransfer(0xff);
		if(cnt++>timeout)
			return SDERR_TIMEOUT;		//No Card
	}while(result!=0xFE);			//theSTART Block;
	//Receive datablock
	for(cnt=0;cnt<length;cnt++)
		sdBuffer[cnt] = SPITransfer(0xff);	//Transfer H to get data
	//Receive CRC
	SPITransfer(0xff);
	SPITransfer(0xff);

	return 0;
}



//===========High level Command===========
unsigned char sdInitCard()
{
	unsigned char result;
	result = sdSendNoDataCommand(0x00,0x00);	//Send Command 0 = 40 00 00 00 00 95h
	result = sdSendNoDataCommand(0x00,0x00);	//Send Command 0 = 40 00 00 00 00 95h
	if(result==0xff)
		return result;					//No card! Exit 1 : CMD0 Error CMD0 Should return 0x01;
	do
	{
		result = sdSendNoDataCommand(0x01,0x00);	//Send Command 1. No argument = argument set to 0
	}while(result);
	return result;						//0=OK, !=0 ==>  Exit2 :CMD1 Error. At last should return 0x00;
}

unsigned char sdSendNoDataCommand(unsigned char index, unsigned long argument)
{										//used by init
	unsigned char result;
	// Assert SS
	assertSS();

	result = sdSendCommand(index,argument);

	// Deassert CS
	deassertSS();
	SPITransfer(0xff);	
	return result;
}

	

unsigned char sdReadCSD()
{
	unsigned char result;
	// Assert SS
	assertSS();
	result = sdSendCommand(0x09,0x00);	//No argument
	sdReceiveDataBlock(16,8);			//Length=16, timeout=8
	deassertSS();
	SPITransfer(0xff);	
	return result;
}	

unsigned char sdReadData(unsigned long address)	// 2 Error exits
{	//Only suitable for default 512 byte mode
	unsigned char result;
	// Assert SS
	assertSS();
	// send Command
	result = sdSendCommand(0x11,address);	//argument=address 
	if(result)
		return result;						//Exit 1: ersponse Error
	result = sdReceiveDataBlock(512,256);			//Length=16, timeout=256
	deassertSS();
	SPITransfer(0xff);	
	return result;							// 0 = OK. !=0 --> Error. Exit 2: TimeOut

}


unsigned char sdWriteData(unsigned long address)	// 
{	//Only suitable for default 512 byte mode
	unsigned char result;
	unsigned short cnt;
	// 1.Assert SS
	assertSS();
	// 2. Send Command & wait for Response
	result = sdSendCommand(0x18,address);	//argument=address
	if(result)
		return result;						//Exit 1 : response Error
	// 3. Write 1 byte H (Nwr>=1)
	SPITransfer(0xFF);
	SPITransfer(0xFF);
	// 4. Write DataBlock
	// 4.1 Start Token
	SPITransfer(0xFE);
	// 4.2 Data
	for(cnt = 0;cnt<512;cnt++)
		SPITransfer(sdBuffer[cnt]);
	// 4.3 CRC & end bit. The last bit should be 1
	SPITransfer(0xFF);
	SPITransfer(0xFF);
	//5. Read DataResponse (immediatly after DataBlock)
	result = SPITransfer(0xFF);
	result &= 0x1F;		//only last 5 bits are meaningful
	if(result!=0x05)
		return result;						//Exit 2 : data response Error

	//6. Wait while Busy
	while(SPITransfer(0xFF) != (unsigned char)0xFF);
	//7. Dessert SS
	deassertSS();
	SPITransfer(0xff);	
	return 0;							// 0=OK, check
}