请教串口开关问题，目前打开DMA时，关闭有错误

发布于 2020-05-06 11:35:16 浏览：1103 订阅该版

串口（DMA）开启之后，可以调用`rt_device_close()`关闭串口，如果继续有数据进入串口显示：
![TIM截图20200506112304.png](/uploads/202005/06/112319l53hkvas1te0nsu9.png)

不论是否出现上述错误，如果再调用`rt_device_open()`，串口无法再次开启。
文档中的 open-close 成对使用，具体是什么意思？如何使用。
希望给个可执行的循环开启关闭案例。    
还有rt-thread 中串口中断怎么开启关闭？   拜托大家帮忙解答一下。

下面是DMA 的示例代码部分加了开启关闭测试：

```c
#include <rtthread.h>
#include <rtdevice.h>
#include <board.h>

#define SAMPLE_UART_NAME       "uart3"      /* 串口设备名称 */

/* 串口接收消息结构*/
struct rx_msg
{
    rt_device_t dev;
    rt_size_t size;
};
/* 串口设备句柄 */
static rt_device_t serial;
/* 消息队列控制块 */
static struct rt_messagequeue rx_mq;

/* 接收数据回调函数 */
static rt_err_t uart_input(rt_device_t dev, rt_size_t size)
{
    struct rx_msg msg;
    rt_err_t result;
    msg.dev = dev;
    msg.size = size;

result = rt_mq_send(&rx_mq, &msg, sizeof(msg));
 if ( result == -RT_EFULL)
 {
 /* 消息队列满 */
 rt_kprintf("message queue full！ ");
 }
 return result;
}

static void serial_thread_entry(void *parameter)
{
    struct rx_msg msg;
    rt_err_t result;
    rt_uint32_t rx_length;
    static char rx_buffer[RT_SERIAL_RB_BUFSZ + 1];

while (1)
 {
 rt_memset(&msg, 0, sizeof(msg));
 /* 从消息队列中读取消息*/
 result = rt_mq_recv(&rx_mq, &msg, sizeof(msg), RT_WAITING_FOREVER);
 if (result == RT_EOK)
 {
 /* 从串口读取数据*/
 rx_length = rt_device_read(msg.dev, 0, rx_buffer, msg.size);
 rx_buffer[rx_length] = '\0';
 /* 通过串口设备 serial 输出读取到的消息 */
 rt_device_write(serial, 0, rx_buffer, rx_length);
 /* 打印数据 */
 rt_kprintf("%s ",rx_buffer);
 }
 }
}

static int uart_dma_sample(int argc, char *argv[])
{
 rt_err_t ret = RT_EOK;
 char uart_name[RT_NAME_MAX];
 static char msg_pool[256];
 char str[] = "hello RT-Thread! ";

if (argc == 2)
    {
        rt_strncpy(uart_name, argv[1], RT_NAME_MAX);
    }
    else
    {
        rt_strncpy(uart_name, SAMPLE_UART_NAME, RT_NAME_MAX);
    }

/* 初始化消息队列 */
 rt_mq_init(&rx_mq, "rx_mq",
 msg_pool, /* 存放消息的缓冲区 */
 sizeof(struct rx_msg), /* 一条消息的最大长度 */
 sizeof(msg_pool), /* 存放消息的缓冲区大小 */
 RT_IPC_FLAG_FIFO); /* 如果有多个线程等待，按照先来先得到的方法分配消息 */
<div>
<span style='display: inline !important; float: none; background-color: rgb(247, 247, 247); color: rgb(51, 51, 51); font-family: arial,"Microsoft Yahei","Hiragino Sans GB",sans-serif; font-size: 14px; font-style: normal; font-variant: normal; font-weight: 400; letter-spacing: normal; orphans: 2; overflow-wrap: break-word; text-align: left; text-decoration: none; text-indent: 0px; text-transform: none; -webkit-text-stroke-width: 0px; white-space: normal; word-spacing: 0px;'>	 /* 查找串口设备 */
<span style='display: inline !important; float: none; background-color: rgb(247, 247, 247); color: rgb(51, 51, 51); font-family: arial,"Microsoft Yahei","Hiragino Sans GB",sans-serif; font-size: 14px; font-style: normal; font-variant: normal; font-weight: 400; letter-spacing: normal; orphans: 2; overflow-wrap: break-word; text-align: left; text-decoration: none; text-indent: 0px; text-transform: none; -webkit-text-stroke-width: 0px; white-space: normal; word-spacing: 0px;'> serial = rt_device_find(SAMPLE_UART_NAME);
<span style='display: inline !important; float: none; background-color: rgb(247, 247, 247); color: rgb(51, 51, 51); font-family: arial,"Microsoft Yahei","Hiragino Sans GB",sans-serif; font-size: 14px; font-style: normal; font-variant: normal; font-weight: 400; letter-spacing: normal; orphans: 2; overflow-wrap: break-word; text-align: left; text-decoration: none; text-indent: 0px; text-transform: none; -webkit-text-stroke-width: 0px; white-space: normal; word-spacing: 0px;'> if (!serial)
<span style='display: inline !important; float: none; background-color: rgb(247, 247, 247); color: rgb(51, 51, 51); font-family: arial,"Microsoft Yahei","Hiragino Sans GB",sans-serif; font-size: 14px; font-style: normal; font-variant: normal; font-weight: 400; letter-spacing: normal; orphans: 2; overflow-wrap: break-word; text-align: left; text-decoration: none; text-indent: 0px; text-transform: none; -webkit-text-stroke-width: 0px; white-space: normal; word-spacing: 0px;'> {
<span style='display: inline !important; float: none; background-color: rgb(247, 247, 247); color: rgb(51, 51, 51); font-family: arial,"Microsoft Yahei","Hiragino Sans GB",sans-serif; font-size: 14px; font-style: normal; font-variant: normal; font-weight: 400; letter-spacing: normal; orphans: 2; overflow-wrap: break-word; text-align: left; text-decoration: none; text-indent: 0px; text-transform: none; -webkit-text-stroke-width: 0px; white-space: normal; word-spacing: 0px;'> rt_kprintf("find %s failed! ", SAMPLE_UART_NAME);
<span style='display: inline !important; float: none; background-color: rgb(247, 247, 247); color: rgb(51, 51, 51); font-family: arial,"Microsoft Yahei","Hiragino Sans GB",sans-serif; font-size: 14px; font-style: normal; font-variant: normal; font-weight: 400; letter-spacing: normal; orphans: 2; overflow-wrap: break-word; text-align: left; text-decoration: none; text-indent: 0px; text-transform: none; -webkit-text-stroke-width: 0px; white-space: normal; word-spacing: 0px;'> }<strike></strike>
</div><div><strike></strike>
</div> /* 创建 serial 线程 */
 rt_thread_t thread = rt_thread_create("serial", serial_thread_entry, RT_NULL, 1024, 25, 10);
 /* 创建成功则启动线程 */
 if (thread != RT_NULL)
 {
 rt_thread_startup(thread);
 }
 else
 {
 ret = RT_ERROR;
 }

return ret;
}
/* 导出到 msh 命令列表中 */
MSH_CMD_EXPORT(uart_dma_sample, uart device dma sample);

static void uart_open_test(void)
{		
	 rt_err_t res;
	 rt_kprintf("this is open! ");
	
		res = rt_device_open(serial, RT_DEVICE_FLAG_DMA_RX);
	 if(res != RT_EOK)
		{
			rt_kprintf("uart3 open failed! ");
		}
		rt_device_set_rx_indicate(serial, uart_input);
}
MSH_CMD_EXPORT(uart_open_test, uart device open);

static void uart_close_test(void)
{
		rt_err_t res;
		rt_kprintf("this is close! ");
		res = rt_device_close(serial);
	 if(res != RT_EOK)
		{
			rt_kprintf("uart3 close failed! ");
		}
}
MSH_CMD_EXPORT(uart_close_test, uart device close);
```