SPI驱动写法的问题

发布于 2019-10-24 10:29:31 浏览：1634 订阅该版

* 本帖最后由 bevis 于 2019-10-24 10:31 编辑 *

根据文档SPI读写方式有几种，在实际应用中使用rt_spi_send_then_recv更容易失败 ，使用 rt_spi_transfer_message反而更容易成功，文档说两者都是一样的关系。以下是我写的两套写法，自认为读写流程都是一样的。结果使用rt_spi_transfer_message成功，前者接口却是失败的。
难道这两套流程不一样吗？？？函数名：
```uint8_t spiTxRx(const uint8_t *txData, uint8_t *rxData, uint16_t length)```

第一段使用rt_spi_send_then_recv   -- 执行结果失败， 我说的失败，不是SPI驱动失败，而是SPI设备读写初始化运行失败
``` if((NULL == txData) && (NULL == rxData))
        {
            return i;
        }
        
        if(length > 128)
        {
                        return i;
        }
        if(txData != NULL)
        {
                memcpy(tx_buff, txData, length);
                if(rxData != NULL)
                {
                        rt_spi_send_then_recv(spi_dev_st25r, tx_buff, length, rx_buff, length);
                        memcpy(rxData, rx_buff, length);
                }
                else // RX NULL, 输入缓冲不能为空
                {
                        rt_spi_send_then_recv(spi_dev_st25r, txData, length, RT_NULL, 0);
                }
        }
        else // TX NULL
        {
                if(rxData != NULL)
                {
                        rt_spi_send_then_recv(spi_dev_st25r, RT_NULL, 0, rx_buff, length);
                        memcpy(rxData, rx_buff, length);
                }
        }
        rt_thread_mdelay(5);
  return i;```

第二段rt_spi_transfer_message -- 成功
``` uint8_t i=0;
        if((NULL == txData) && (NULL == rxData))
        {
            return i;
        }
        
        if(length > 128)
        {
                        return i;
        }
        struct rt_spi_message msg1, msg2;
        if(txData != NULL)
        {
                if(rxData != NULL) // RX 非空
                {
                        msg1.send_buf   = txData; // 发送缓存
                        msg1.recv_buf   = rx_buff;// 接收缓存
                        msg1.length     = length;
                        msg1.cs_take    = 1;
                        msg1.cs_release = 0;
                        msg1.next       = &msg2;

msg2.send_buf   = RT_NULL;
                        msg2.recv_buf   = RT_NULL; 
                        msg2.length     = 0;
                        msg2.cs_take    = 0;
                        msg2.cs_release = 1;
                        msg2.next       = RT_NULL;
                        rt_spi_transfer_message(spi_dev_st25r, &msg1);
                        memcpy(rxData, rx_buff, length);
                }
                else // RX NULL
                {
                        msg1.send_buf   = txData; // 发送缓存
                        msg1.recv_buf   = RT_NULL;
                        msg1.length     = length; // 发送长度
                        msg1.cs_take    = 1;
                        msg1.cs_release = 0;
                        msg1.next       = &msg2;

msg2.send_buf   = RT_NULL;
                        msg2.recv_buf   = RT_NULL;
                        msg2.length     = 0;
                        msg2.cs_take    = 0;
                        msg2.cs_release = 1;
                        msg2.next       = RT_NULL;
                        rt_spi_transfer_message(spi_dev_st25r, &msg1);
                }
        }
        else // TX NULL
        {
                if(rxData != NULL) // RX 非空
                {
                        msg1.send_buf   = RT_NULL;
                        msg1.recv_buf   = RT_NULL;
                        msg1.length     = 0;
                        msg1.cs_take    = 1;
                        msg1.cs_release = 0;
                        msg1.next       = &msg2;

msg2.send_buf   = RT_NULL;
                        msg2.recv_buf   = rx_buff; // 接收缓存
                        msg2.length     = length;
                        msg2.cs_take    = 0;
                        msg2.cs_release = 1;
                        msg2.next       = RT_NULL;
                        rt_spi_transfer_message(spi_dev_st25r, &msg1);
                        memcpy(rxData, rx_buff, length);
                }
        }
        rt_thread_mdelay(5);
  return i;```