sd.c

7s64mp3系统开发软件

/************************************************************/
/*		 SD Code for   AT91SAM7S64						*/
/*				By   pasyong								*/
/*					2006-5									*/
/*				Base IAR 4.30A						*/
/************************************************************/
/*-----------------------------------------------------------------------
硬件连接      SD_CS-----------PA25
-----------------------------------------------------------------------*/
#include "ioat91sam7s64.h"
#include "uart.h"
#include "vs1011.h"
#define uchar unsigned char
#define uint unsigned int
#define SD_CS     ((unsigned int) 1 <<25)

 extern uchar BUFFER[512];
uchar reading;
//一个扇区缓冲区
void delay_Nus(unsigned int n)
	{
	unsigned char  b;
		for (b = 1; b<n; b++)
			;
	}

/*-----------------------------------------------------------------------
PORT_INIT函数
-----------------------------------------------------------------------*/
void SD_port_init(void)
{
SPI_init();
*AT91C_PIOA_PER|=SD_CS;
   //作为I/O使用
*AT91C_PIOA_OER|=SD_CS;
  //输出
*AT91C_PIOA_SODR|=SD_CS;
  //输出高电平
}

//****************************************************************************
//Send a Command to SD-Card
//Return: the second byte of response register of 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)
  *AT91C_PIOA_CODR|=SD_CS;      //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)
   *AT91C_PIOA_SODR|=SD_CS;           //MMC_CS_PIN=1;
   else *AT91C_PIOA_CODR|=SD_CS;       //MMC_CS_PIN=0;
   return(tmp);
}
//****************************************************************************
//SD卡初始化(SPI-MODE)
//****************************************************************************
uchar SD_Init(void)
{
   uchar retry,temp;
   uchar i;
   *AT91C_PIOA_CODR|=SD_CS;       //SD卡使能

  delay_Nus(250);  //Wait MMC/SD ready...
   for (i=0;i<16;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

   *AT91C_PIOA_SODR|=SD_CS;    //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，才拿继续
   for(i=0; i<512; i++)
	{
	BUFFER[i]=Read_Byte_SPI();
	}
   Read_Byte_SPI();//CRC - Byte
   Read_Byte_SPI();//CRC - Byte
   reading=0;
   *AT91C_PIOA_SODR|=SD_CS;         //关闭SD卡
   return(temp);
}