SPI数据写入/读取

Question

我使用下面的命令将数据从SPI Core传递到闪存或SD卡等。

XSpi_Transfer(&Spi, SendData, ResData, 1);

我知道为了在内存中保存\读取数据，我们需要给出一个地址。

但我不明白的是如何在上面的命令中指定地址。

Answer 1

此github page显示了一个名为SpiAtmelFlashRead的示例函数，语法如下：

SPI_Status = SpiAtmelFlashRead(&spi, Address, ByteCount);

read函数内部的代码是：

/*****************************************************************************/
/**
*
* This function reads data from the Atmel Flash device connected to the SPI
* interface.
*
* @param    SpiPtr is a pointer to the SPI driver component to use.
* @param    Addr is the address from which the data is to be read from
*       the Flash.
* @param    ByteCount is the number of bytes to read.
*
* @return   XST_SUCCESS if successful else XST_FAILURE.
*
* @note     None.
*
******************************************************************************/
int SpiAtmelFlashRead(XSpi *SpiPtr, u32 Address, u16 ByteCount)
{
    u16 Index;

    /*
     * Setup the read command with the specified address and data for the
     * Atmel Flash.
     */
    WriteBuffer[ATMEL_COMMAND_OFFSET]   = ATMEL_COMMAND_READ;
    WriteBuffer[ATMEL_ADDRESS_BYTE1_OFFSET] = (u8) (Address >> 16);
    WriteBuffer[ATMEL_ADDRESS_BYTE2_OFFSET] = (u8) (Address >> 8);
    WriteBuffer[ATMEL_ADDRESS_BYTE3_OFFSET] = (u8) Address;

    /*
     * Prepare the write buffer. Fill in some dummy data.
     */
    for(Index = 4; Index < (ByteCount + ATMEL_READ_WRITE_EXTRA_BYTES);
                Index++) {
        WriteBuffer[Index] = ATMEL_DUMMYBYTE;
    }

    /*
     * Prepare the Read Buffer. Fill in some initialization data into the
     * the buffer.
     */
    for(Index = 0; Index < (ByteCount +
                ATMEL_READ_WRITE_EXTRA_BYTES); Index++) {
        ReadBuffer[Index] = ATMEL_INITBYTE;
    }

    /*
     * Send the read command to the Atmel Flash to read the specified number
     * of bytes.
     */
    TransferInProgress = TRUE;
    XSpi_Transfer(SpiPtr, WriteBuffer, ReadBuffer,
                ByteCount + ATMEL_READ_WRITE_EXTRA_BYTES);

    /*
     * Wait till the Transfer is complete and check if there are any errors
     * in the transaction.
     */
    while (TransferInProgress);
    if(ErrorCount != 0) {
        ErrorCount = 0;
        return XST_FAILURE;
    }

    return XST_SUCCESS;
}

此github page显示了一个名为SpiAtmelFlashWrite的示例函数，语法如下：

SPI_Status = SpiAtmelFlashWrite(&spi, Address, chunk, ByteCount);

write函数内部的代码是：

/*****************************************************************************/
/**
*
* This function writes to the Atmel Flash device connected to the SPI interface.
*
* @param    SpiPtr is a pointer to the SPI driver component to use.
* @param    Address is the address to which the data is written.
* @param    ByteCount contains the number of bytes to write.
*
* @return   XST_SUCCESS if successful else XST_FAILURE.
*
* @note     None.
*
******************************************************************************/
int SpiAtmelFlashWrite(XSpi *SpiPtr, u32 Address, u16 ByteCount)
{
    u16 Index;

    /*
     * Setup the write command with the specified address, and data to be
     * written to the flash.
     */
    WriteBuffer[ATMEL_COMMAND_OFFSET]     = ATMEL_COMMAND_WRITE;
    WriteBuffer[ATMEL_ADDRESS_BYTE1_OFFSET] = (u8) (Address >> 16);
    WriteBuffer[ATMEL_ADDRESS_BYTE2_OFFSET] = (u8) (Address >> 8);
    WriteBuffer[ATMEL_ADDRESS_BYTE3_OFFSET] = (u8) (Address);

    /*
     * Prepare the write buffer. Fill in the data that is to be written into
     * the Flash.
     */
    for(Index = 4; Index < (ByteCount + ATMEL_READ_WRITE_EXTRA_BYTES);
            Index++) {
        WriteBuffer[Index] = (u8)(ATMEL_TEST_BYTE + Index);
    }

    /*
     * Send the write command, address, and data to the Flash.
     * No receive buffer is specified since there is nothing to receive.
     */
    TransferInProgress = TRUE;
    XSpi_Transfer(SpiPtr, WriteBuffer, NULL,
            ByteCount + ATMEL_READ_WRITE_EXTRA_BYTES)
                            ;

    /*
     * Wait till the Transfer is complete and check if there are any errors
     * in the transaction.
     */
    while (TransferInProgress);
    if(ErrorCount != 0) {
        ErrorCount = 0;
        return XST_FAILURE;
    }

    return XST_SUCCESS;
}

Answer 2

与外部存储设备通信的实际协议将在其数据手册中指定(即，向芯片发送地址和命令的方式因制造商和产品线而异)。看起来您的函数只是简单地启动了一个SPI传输。您很可能需要多次调用该函数来发送特定的字节/字序列，这些字节/字序列共同构成了写命令、地址和数据。同样，这一切都取决于数据表。了解一下XSpi_Transfer中到底发生了什么也会很有帮助。

还要记住，要确保在SPI配置例程中正确设置SPI极性、相位和数据位。