下圖是萬利板子的SD卡部分

其中SD_PWR連接到了 PD10 通過一個控制

P-Channel 2.5-V (G-S) MOSFET 控制SD卡的電源

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SPI模式 讀寫SD卡

SD卡初始化過程：

1. 初始化STM32的SPI接口 使用低速模式
2. 延時至少74clock
3. 發(fā)送CMD0，需要返回0x01，進入Idle狀態(tài)
4. 循環(huán)發(fā)送CMD55+ACMD41，直到返回0x00，進入Ready狀態(tài)
5. 設置讀寫block大小為512byte
5. 把STM32的SPI設置為高速模式



讀一個block塊的過程

1. 發(fā)送CMD17（單塊）或CMD18（多塊）讀命令，返回0x00
2. 接收數(shù)據(jù)開始令牌0xfe + 正式數(shù)據(jù)512Bytes + CRC 校驗2Bytes

寫一個block塊的過程

1. 發(fā)送CMD24（單塊）或CMD25（多塊）寫命令，返回0x00
2. 發(fā)送數(shù)據(jù)開始令牌0xfe + 正式數(shù)據(jù)512Bytes + CRC校驗2Bytes

/*******************************************************************************
* Function Name : SD_MMC_SPI_Init
* Description : SD_MMC_SPI_Init
* Input : None
* Output : None
* Return : zero init success, non-zero init error
*******************************************************************************/
u8 SD_MMC_SPI_Init(void)
{
GPIO_InitTypeDef GPIO_InitStructure;

/* Enable SPI1 and GPIO clocks */
RCC_APB2PeriphClockCmd(RCC_APB2Periph_SPI1 | RCC_APB2Periph_GPIOA |
RCC_APB2Periph_SD_MMC_SPI_CS, ENABLE);

/* Configure SPI1 pins: SCK, MISO and MOSI */
GPIO_InitStructure.GPIO_Pin = GPIO_Pin_5 | GPIO_Pin_6 | GPIO_Pin_7;
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF_PP;
GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
GPIO_Init(GPIOA, &GPIO_InitStructure);

/* Configure SD_MMC_SPI_CS */
GPIO_InitStructure.GPIO_Pin = SD_MMC_SPI_CS_Pin_CS;
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_Out_PP;
GPIO_Init(SD_MMC_SPI_CS, &GPIO_InitStructure);

//////////////////////////////////////////////////////////////////////////////
/* initialize SPI with lowest frequency */
SD_MMC_Low_Speed();

/* card needs 74 cycles minimum to start up */
for(u8 i = 0; i < 10; ++i)
{
/* wait 8 clock cycles */
SD_MMC_ReadWrite_Byte(0x00);
}

/* address card */
SD_MMC_SPI_SELECT();

/* reset card */
u8 response;
for(u16 i = 0; ; ++i)
{
response = SD_MMC_Send_Command(CMD_GO_IDLE_STATE , 0 );
if( response == 0x01 )
break;

if(i == 0x1ff)
{
SD_MMC_SPI_DESELECT();
return 1;
}
}

/* wait for card to get ready */
for(u16 i = 0; ; ++i)
{
response = SD_MMC_Send_Command(CMD_SEND_OP_COND, 0);
if(!(response & (1 << R1_IDLE_STATE)))
break;

if(i == 0x7fff)
{
SD_MMC_SPI_DESELECT();
return 1;
}
}

/* set block size to 512 bytes */
if(SD_MMC_Send_Command(CMD_SET_BLOCKLEN, 512))
{
SD_MMC_SPI_DESELECT();
return 1;
}

/* deaddress card */
SD_MMC_SPI_DESELECT();

/* switch to highest SPI frequency possible */
SD_MMC_High_Speed();

return 0;
//////////////////////////////////////////////////////////////////////////////
}

/*******************************************************************************
* Function Name : SD_MMC_Read_Single_Block
* Description : SD_MMC_Read_Single_Block
* Input : sector number and buffer data point
* Output : None
* Return : zero success, non-zero error
*******************************************************************************/
u8 SD_MMC_Read_Single_Block(u32 sector, u8* buffer)
{
u8 Response;
u16 i;
u16 Retry = 0;

//讀命令 send read command
Response = SD_MMC_Send_Command(CMD_READ_SINGLE_BLOCK, sector<<9);

if(Response != 0x00)
return Response;

SD_MMC_SPI_SELECT();

// start byte 0xfe
while(SD_MMC_ReadWrite_Byte(0xff) != 0xfe)
{
if(++Retry > 0xfffe)
{
SD_MMC_SPI_DESELECT();
return 1; //timeout
}
}

for(i = 0; i < 512; ++i)
{
//讀512個數(shù)據(jù)
*buffer++ = SD_MMC_ReadWrite_Byte(0xff);
}

SD_MMC_ReadWrite_Byte(0xff); //偽crc
SD_MMC_ReadWrite_Byte(0xff); //偽crc

SD_MMC_SPI_DESELECT();
SD_MMC_ReadWrite_Byte(0xff); // extra 8 CLK

return 0;
}

/*******************************************************************************
* Function Name : SD_MMC_Write_Single_Block
* Description : SD_MMC_Write_Single_Block
* Input : sector number and buffer data point
* Output : None
* Return : zero success, non-zero error.
*******************************************************************************/
u8 SD_MMC_Write_Single_Block(u32 sector, u8* buffer)
{
u8 Response;
u16 i;
u16 retry=0;

//寫命令 send write command
Response = SD_MMC_Send_Command(CMD_WRITE_SINGLE_BLOCK, sector<<9);
if(Response != 0x00)
return Response;

SD_MMC_SPI_SELECT();

SD_MMC_ReadWrite_Byte(0xff);
SD_MMC_ReadWrite_Byte(0xff);
SD_MMC_ReadWrite_Byte(0xff);

//發(fā)開始符 start byte 0xfe
SD_MMC_ReadWrite_Byte(0xfe);

//送512字節(jié)數(shù)據(jù) send 512 bytes data
for(i=0; i<512; i++)
{
SD_MMC_ReadWrite_Byte(*buffer++);
}

SD_MMC_ReadWrite_Byte(0xff); //dummy crc
SD_MMC_ReadWrite_Byte(0xff); //dummy crc

Response = SD_MMC_ReadWrite_Byte(0xff);

//等待是否成功 judge if it successful
if( (Response&0x1f) != 0x05)
{
SD_MMC_SPI_DESELECT();
return Response;
}
//等待操作完 wait no busy
while(SD_MMC_ReadWrite_Byte(0xff) != 0x00)
{
if(retry++ > 0xfffe)
{
SD_MMC_SPI_DESELECT();
return 1;
}
}
SD_MMC_SPI_DESELECT();
SD_MMC_ReadWrite_Byte(0xff);// extra 8 CLK

return 0;
}

if( SD_MMC_SPI_Init() ==1)
printf(" _SD_MMC Initialization ERRORrn");
else
{
printf(" _SD_MMC Initialization OKrn");
//memset(buffer,0,512);
//讀取一個扇區(qū)的內容 這里讀的是0扇區(qū)
SD_MMC_Read_Single_Block( 0 , buffer );
Uart1_PutString( buffer , 512 );
}