STM32 Development Board Getting Started Tutorial (Thirteen) - SPI Mode Read and Write SD Card-EEWORLD

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Function introduction: Use SPI mode to read and write SD card block data and send it to PC through serial port for viewing

SD card is the abbreviation of Secure Digital Card, which literally translates into Chinese as "Secure Digital Card". It is a brand-new memory card product jointly developed by Japan's Panasonic, Toshiba and the United States' SANDISK. SD memory card is a completely open standard (system), which is mostly used in MP3, digital video cameras, digital cameras, e-books, AV equipment, etc., especially widely used in ultra-thin digital cameras. Haha, why do we like to use SD cards when making things now? It has a large capacity and a low price. The number of read and write times is more than 100,000 times (some data say it is 300,000 times, haha). This number is powerful enough, and the reading and writing speed is also very fast. Now the high-speed SD card can write at a speed of up to 20M/S. Haha, if the SD card you bought cannot reach this speed, you should consider whether you have bought a fake. Haha, SD cards are very cheap now. It seems that a 4G card is only 50 yuan each.

Well, let's not go off topic, let's get back to the point. There are two ways to read and write SD cards, one is SD mode and the other is SPI mode. The SD mode has a complex operation timing and uses many IO ports. The commonly used mode is SPI mode. The SPI mode we introduce today is also simple in interface and easy to transplant. The speed is not slow. Using the high-speed SPI mode, 1M/S should be easy to achieve. I just transplanted the SD card reading and writing under STM32, but I didn't test the reading and writing speed. I'll test the reading and writing speed next time I have time and post it.

SD card initialization process:

1. Initialize the SPI interface of STM32 to use low-speed mode
2. Delay at least 74clock
3. Send CMD0, need to return 0x01, enter Idle state
4. Loop and send CMD55+ACMD41 until it returns 0x00 and enters Ready state
5. Set the read and write block size to 512byte
5. Set the STM32 SPI to high-speed mode

The process of reading a block

1. Send CMD17 (single block) or CMD18 (multiple blocks) read command, return 0x00
2. Receive data start token 0xfe + formal data 512Bytes + CRC check 2Bytes

The process of writing a block

1. Send CMD24 (single block) or CMD25 (multiple blocks) write command, return 0x00
2. Send data start token 0xfe + formal data 512Bytes + CRC check 2Bytes

Attach a datasheet with the standard spi mode initialization flow

初始化函数
/*******************************************************************************
* 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;
}

Send a command
/********************************************** *********************************
* Function Name: SD_MMC_Send_Command
* Description: SD_MMC_Send_Command
* Input: None
* Output: None
* Return: None
********************************************** *********************************/
u8 SD_MMC_Send_Command(u8 cmd, u32 arg)
{
       u8 Response;
       u8 Retry = 0;
       SD_MMC_ReadWrite_Byte(0xff);
       SD_MMC_SPI_SELECT();
       //Write commands respectively
       SD_MMC_ReadWrite_Byte(cmd | 0x40);
       SD_MMC_ReadWrite_Byte(arg >> 24);
       SD_MMC_ReadWrite_Byte(arg >> 16);
       SD_MMC_ReadWrite_Byte(arg >> 8);
       SD_MMC_ReadWrite_Byte(arg);
       SD_MMC_ReadWrite_Byte(0x95);

       do{
            // Wait for response, the start bit of the response is 0
            Response = SD_MMC_ReadWrite_Byte(0xff);
            Retry++;
       }while( ((Response&0x80)!=0) && (Retry < 200) ) ;
       SD_MMC_SPI_DESELECT();
       return Response; //Return status value
}

读一个block块读取成功返回0 非0 则读取失败
/*******************************************************************************
* 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;
      //读命令 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)
       {
            //读512个数据
            *buffer++ = SD_MMC_ReadWrite_Byte(0xff);
       }
       SD_MMC_ReadWrite_Byte(0xff);   //伪crc
       SD_MMC_ReadWrite_Byte(0xff);   //伪crc
       SD_MMC_SPI_DESELECT();
       SD_MMC_ReadWrite_Byte(0xff);   // extra 8 CLK
       return 0;
}

写一个block块成功返回0 非0 则写入失败
/*******************************************************************************
* 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;

       //写命令   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);
       //发开始符 start byte 0xfe
SD_MMC_ReadWrite_Byte(0xfe);

       //送512字节数据 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;
}

Keywords：STM32 Reference address：STM32 Development Board Getting Started Tutorial (Thirteen) - SPI Mode Read and Write SD Card

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