sd.c~

以AVRMEGA32播放SD卡中的WAV音乐

#include "sd.h"






//低速模式 
void SPI_Low(void)
{
	SPCR =0x52;//_BV(SPE)|_BV(MSTR)|_BV(SPR1)|_BV(SPR0);
	SPSR &= 0xfe;        //关双速
}

//高速模式
void SPI_High(void)
{
	SPCR =0x50;//  _BV(SPE)|_BV(MSTR);
	SPSR |=0x01;// _BV(SPI2X); //开双速
}

//端口初始化，模式初始化  
void SPI_Init(void)
{
	DDR_INI();  //端口设置，主要是SPI
	SPI_Low(); //先低速
}



//sd卡初始化		
void MMC_SD_Init(void)
{
	SPI_Init();
	SPI_CS_Deassert();//cs=1
}


//写读一个字节			//read and write one byte
uint8 SPI_WriteByte(uint8 val)
{
	SPDR = val;
	while(SPSR.7==0);
	return SPDR;
}



//sd卡写命令		
uint8 MMC_SD_SendCommand(uint8 cmd, uint32 arg)
{
	uint8 r1;
	uint8 retry=0;
	
	SPI_WriteByte(0xff);
	SPI_CS_Assert();  //CS=0
	
	SPI_WriteByte(cmd | 0x40);//分别写入命令	
	SPI_WriteByte(arg>>24);
	SPI_WriteByte(arg>>16);
	SPI_WriteByte(arg>>8);
	SPI_WriteByte(arg);
	SPI_WriteByte(0x95);
	
	while((r1 = SPI_WriteByte(0xff)) == 0xff)//等待响应，	
		if(retry++ > 100) break;//超时退出		

	SPI_CS_Deassert();   //cs=1

	return r1;//返回状态值					
}

//sd卡复位		
uint8 MMC_SD_Reset(void)
{
	uint8 i;
	uint8 retry;
	uint8 r1=0;
	retry = 0;
	SPI_Low();
        SPI_CS_Deassert();//
	for(i=0; i<16; i++)
      SPI_WriteByte(0xFF);
     
	do
	{
		for(i=0;i<20;i++) SPI_WriteByte(0xff);
		r1 = MMC_SD_SendCommand(0, 0);//发idle命令
		retry++; 
		//TransmitByte(retry);
		if(retry>200) return 1;//超时退出	
	} while(r1 != 0x01);	


	retry = 0;
	do
	{
		r1 = MMC_SD_SendCommand(1, 0);//发active命令	
		retry++;
		if(retry>100) return 1;//超时退出		
	} while(r1);
	SPI_High();
	r1 = MMC_SD_SendCommand(59, 0);//关crc		

	r1 = MMC_SD_SendCommand(16, 512);//设扇区大小512
	return 0;//正常返回	
}

//读一个扇区		
uint8 MMC_SD_ReadSingleBlock(uint32 sector, uint8* buffer)
{
	uint8 r1;
	uint16 i;
	uint16 retry=0;
        SPI_CS_Deassert();//
	for(i=0; i<16; i++)
      SPI_WriteByte(0xFF);
	r1 = MMC_SD_SendCommand(17, sector<<9);//读命令	/9
	
	if(r1 != 0x00)
		return r1;

	SPI_CS_Assert();  //cs=0
	//等数据的开始	
	while(SPI_WriteByte(0xff) != 0xfe)if(retry++ > 1000){SPI_CS_Deassert();return 1;}

	for(i=0; i<512; i++)//读512个数据	
	{
		*buffer++ = SPI_WriteByte(0xff);
	}

	SPI_WriteByte(0xff);//伪crc
	SPI_WriteByte(0xff);
	
	SPI_CS_Deassert(); //cs=1

	return 0;
}
/* 
//读一个扇区		
uint8 MMC_SD_ReadSingleBlock1(uint32 sector, uint8* buffer)
{
	uint8 r1;
	uint16 i;
	uint16 retry=0;
         MMC_SD_SendCommand(16, 256);
	r1 = MMC_SD_SendCommand(17, sector<<8);//读命令	/9
	
	if(r1 != 0x00)
		return r1;

	SPI_CS_Assert();  //cs=0
	//等数据的开始	
	while(SPI_WriteByte(0xff) != 0xfe)if(retry++ > 1000){SPI_CS_Deassert();return 1;}

	for(i=0; i<256; i++)//读512个数据	
	{
		*buffer++ = SPI_WriteByte(0xff);
	}

	SPI_WriteByte(0xff);//伪crc
	SPI_WriteByte(0xff);
	
	SPI_CS_Deassert(); //cs=1

	return 0;
} 
*/