sd.i

以AVRMEGA32播放SD卡中的WAV音乐

 

extern unsigned char MMC_SD_SendCommand(unsigned char cmd, unsigned long arg);
extern void MMC_SD_Init (void); 

extern unsigned char MMC_SD_Reset(void);

extern unsigned char MMC_SD_ReadSingleBlock(unsigned long sector, unsigned char* buffer);

extern void SPI_High(void);








//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)
{
	DDRB |=0xbf  ;  //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();
	PORTB.2=1;//cs=1
}


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

//sd卡写命令		
unsigned char MMC_SD_SendCommand(unsigned char cmd, unsigned long arg)
{
	unsigned char r1;
	unsigned char retry=0;
	
	SPI_WriteByte(0xff);
	PORTB.2=0  ;  //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++ > 20) break;//超时退出		

	PORTB.2=1;   //cs=1

	return r1;//返回状态值					
}

//sd卡复位		
unsigned char MMC_SD_Reset(void)
{
	unsigned char i;
	unsigned char retry;
	unsigned char r1=0;
	retry = 0;
	SPI_Low();
	do
	{
		for(i=0;i<10;i++) SPI_WriteByte(0xff);
		r1 = MMC_SD_SendCommand(0, 0);//发idle命令
		retry++;
		if(retry>10) 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		
unsigned char MMC_SD_ReadSingleBlock(unsigned long sector, unsigned char* buffer)
{
	unsigned char r1;
	unsigned int i;
	unsigned int retry=0;

	r1 = MMC_SD_SendCommand(17, sector<<9);//读命令	/9
	
	if(r1 != 0x00)
		return r1;

	PORTB.2=0  ;  //cs=0
	//等数据的开始	
	while(SPI_WriteByte(0xff) != 0xfe)if(retry++ > 1000){PORTB.2=1;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);
	
	PORTB.2=1; //cs=1

	return 0;
}