uchar reading=0,a=0,pointer=0;
void sd_port_init()
{
MMC_PORT|=MMC_CS_PIN;
}
uchar BUFFER[512]; //扇区缓冲区
uint i=0;
void delay_nus(uint n)
{
unsigned char b;
for (b = 1; b;
}
//****************************************************************************
//Send a Command to MMC/SD-Card
//Return: the second byte of response register of MMC/SD-Card
//****************************************************************************
uchar SD_Write_Command(uchar cmd,unsigned long arg)
{
uchar tmp;
uchar retry=0;

//MMC_PORT|=MMC_CS_PIN; //SD卡关闭
//send 8 Clock Impulse
Write_Byte_SPI(0xFF);

//set MMC_Chip_Select to low (MMC/SD-Card active)
MMC_PORT&=~MMC_CS_PIN; //SD卡使能

Write_Byte_SPI(cmd|0x40); //送头命令
Write_Byte_SPI(arg>>24);
Write_Byte_SPI(arg>>16); //send 6 Byte Command to MMC/SD-Card
Write_Byte_SPI(arg>>8);
Write_Byte_SPI(arg&0xff);
Write_Byte_SPI(0x95); //仅仅对RESET有效的CRC效验码

//get 8 bit response
//Read_Byte_MMC(); //read the first byte,ignore it.
do
{ //Only last 8 bit is used here.Read it out.
tmp = Read_Byte_SPI();
retry++;
}
while((tmp==0xff)&&(retry<100)); //当没有收到有效的命令的时候

if(reading==0)
MMC_PORT|=MMC_CS_PIN; //MMC_CS_PIN=1;
else MMC_PORT&=~MMC_CS_PIN; //MMC_CS_PIN=0;
return(tmp);
}
//****************************************************************************
//SD卡初始化(SPI-MODE)
//****************************************************************************
uchar SD_Init(void)
{
uchar retry,temp;
uchar i;
MMC_PORT&=~MMC_CS_PIN; //SD卡使能

delay_nus(250); //Wait MMC/SD ready...
for (i=0;i<0x0f;i++)
{
Write_Byte_SPI(0xff); //send 74 clock at least!!!
}
//Send Command CMD0 to MMC/SD Card
retry=0;

do
{ //retry 200 times to send CMD0 command
temp=SD_Write_Command(0,0);
retry++;
if(retry==100)
{
;//CMD0 Error!
}
}
while(temp!=1);

//Send Command CMD1 to MMC/SD-Card
retry=0;
do
{ //retry 100 times to send CMD1 command
temp=SD_Write_Command(1,0);
retry++;
if(retry==100)
{
;
}
}
while(temp!=0);
retry=0;
SD_Write_Command(16,512); //设置一次读写BLOCK的长度为512个字节

MMC_PORT|=MMC_CS_PIN; //MMC_CS_PIN=1; //set MMC_Chip_Select to high
return(0); //All commands have been taken.
}
//****************************************************************************
//从SD卡读一个扇区 Return 0 if no Error.
//****************************************************************************
uchar SD_Read_Block(unsigned long address)
{
uchar temp=0;uint i=0;
reading=1;
temp=SD_Write_Command(17,address); //读出RESPONSE
while (Read_Byte_SPI()!= 0xfe)
{;} //直到读取到了数据的开始头0XFE,才继续
for(i=0; i<512; i++)
{
BUFFER[i]=Read_Byte_SPI();
}
Read_Byte_SPI();//CRC - Byte
Read_Byte_SPI();//CRC - Byte
reading=0;
MMC_PORT|=MMC_CS_PIN; //关闭SD卡
return(temp);
}