修改串口波特率，去掉打印信息后打不开串口是为什么？

修改串口波特率，代码如下，去掉打印信息就是close先关闭串口 control修改波特率 open打开串口但是不成功，还是按照115200发送数据，BRR里也是0x16C

rt_uint8_t change_baud(int baud)
{
rt_uint8_t i = 0;
rt_err_t flag = 100, flag_open = 100, flag_close = 100, flag_open2 = 100;//非法值，非RT_EOK
struct serial_configure config = RT_SERIAL_CONFIG_DEFAULT;
/* step1：查找串口设备 */
serial = rt_device_find("uart4");
rt_device_close( serial );
config.baud_rate = baud; //修改波特率为 9600
// config.bufsz = 4096;
for(i = 0; i < 20; i++)//循环10次，成功的话跳出循环
{
rt_kprintf("%d---------\n",i);
rt_kprintf(" before close ue = %0x\n", UART4->CR1);
flag_close = rt_device_close( serial );
rt_kprintf("flag_close = %d\n", flag_close);
USART_Cmd(UART4, DISABLE);
rt_kprintf(" after close ue = %0x\n", UART4->CR1);
if (flag_close == RT_EOK)
{
rt_kprintf("serial close chenggong " );
}
rt_kprintf(" ue = %0x\n", UART4->CR1);
flag = rt_device_control(serial, RT_DEVICE_CTRL_CONFIG, &config);
rt_kprintf("baud = %d brr = %0x\n", baud, UART4->BRR);
if (flag == RT_EOK)
{
flag_open2 = rt_device_open(serial, RT_DEVICE_FLAG_DMA_RX);
rt_kprintf("baud = %d brr = %0x\n", baud, UART4->BRR);
rt_kprintf("flag_open2 = %d\n", flag_open2);
rt_kprintf(" before open ue = %0x\n", UART4->CR1);
USART_Cmd(UART4, ENABLE);
rt_kprintf(" ofter open ue = %0x\n", UART4->CR1);
// if (flag_open2 == RT_EOK)
{
rt_kprintf("serial open chenggong " );
}
rt_kprintf(" change baud %d success\n",baud);
return 1;
}
}
rt_kprintf(" change baud %d failed\n",baud);
flag_open = rt_device_open(serial, RT_DEVICE_FLAG_DMA_RX);
rt_kprintf("flag_open = %d\n", flag_open);
if (flag_open == RT_EOK)
{
rt_kprintf("serial open chenggong " );
}
return 0;
// rt_device_open(serial, RT_DEVICE_FLAG_DMA_RX);
}
自己写了一下，这样就可以了

rt_uint8_t change_baud(int baud)
{
USART_Cmd(UART4, DISABLE);
if (baud == 115200)
{
UART4->BRR = 0x16C;
}
else if (baud == 9600)
{
UART4->BRR = 0x1117;
}
USART_Cmd(UART4, ENABLE);
}