13 UART相关

13.1 UART的RX唤醒MCU怎么做

以下是MCU处于睡眠模式时的唤醒源：

如果您要从Deep/Standby睡眠模式中唤醒，可以看到并没有uart唤醒的功能，因此需要把UART的RX配置为GPIO模式，然后启用此IO的唤醒功能，请参阅例程\example\rt_device\pm\project\hcpu，如下所示：

HAL_PIN_Set(PAD_PA26, USART2_TXD, PIN_PULLUP, 1); //uart2 default setting
HAL_PIN_Set(PAD_PA27, USART2_RXD, PIN_PULLUP, 1); //uart2 default setting 

static void gpio_wakeup_handler(void *args)
{
    rt_kprintf("gpio_wakeup_handler!\n");
    HAL_PIN_Set(PAD_PA27, USART2_RXD, PIN_PULLUP, 1); //switch to uart function
    rt_pm_request(PM_SLEEP_MODE_IDLE); //set MCU not to sleep
}
#if defined(SF32LB52X)
{
    HAL_PIN_Set(PAD_PA27, GPIO_A27, PIN_PULLUP, 1); //set PA27 to GPIO funtion

    HAL_HPAON_EnableWakeupSrc(HPAON_WAKEUP_SRC_PIN3, AON_PIN_MODE_POS_EDGE); //Enable #WKUP_PIN3 (PA27)

    rt_pin_mode(27, PIN_MODE_INPUT);

    rt_pin_attach_irq(27, PIN_IRQ_MODE_RISING, (void *) gpio_wakeup_handler,\
                (void *)(rt_uint32_t) 27); //PA34 GPIO interrupt
    rt_pin_irq_enable(27, 1);
}
#endif

建议使用独立的GPIO来唤醒MCU（大多数客户都是这样），如果你想让wakepin和uart rx2共享相同的GPIO，你需要像上面这样做更多的软件工作。等待唤醒完成（看到打印[pm]W:）后，才能接收UART数据，并保持mcu唤醒，直到rx工作完成。

13.2 UART1不进入RX中断回调函数问题

根本原因：
1，UART FIFO has only one byte. If the system is busy, a byte length is about 10 bits, and at 115200 baud rate, it takes about 1us. If the FIFO is not cleared within 1us after receiving the interrupt, it will overflow;;
2，The USART1_IRQHandler interrupt can come in, but due to an error, there is no upper layer callback. The upper layer callback occurs only when data is received normally;。Since Uart1 is used to control audio Bluetooth and changed to Segger printing and system polling, it may cause RX interrupt not to be cleared in time;。
解决方案：
改成DMA RX中断。
rt_device_open(g_bt_uart, RT_DEVICE_FLAG_INT_RX); 改成 rt_device_open(g_bt_uart, RT_DEVICE_FLAG_DMA_RX);

13.3 UART不用rt_kprintf怎么打印Log

1. rt_kprintf
   

rt_kprintf("app_cache_alloc: size %d failed!\n", size);

rt_kprintf打印不受其他开关影响,会一直有打印,适合短期调试,后续可以删掉,此类log不能太多,会影响系统速度
2. Ulog打印
Ulog的打印,是可以分级别输出的,当级别DBG_LEVEL调整到DBG_ERROR后,比它级别低的DBG_WARNING,DBG_INFO,DBG_LOG都不会再输出

#define DBG_LEVEL          DBG_ERROR  // DBG_LOG //
#define LOG_TAG              "drv.it7259e"
#include <drv_log.h>
void init(void)
{
    LOG_D("it7259e touch_init\n");
}

3. 操作UART寄存器打印
   在有些情形下,比如bootloader或RTT操作系统还没起来的情况下,需要Log调试,可以采用下面方法,使用的前提是hwp_usart1已经初始化过,uart初始化方法可以参考例程example\uart\src

char *boot_tag = "0x";
void boot_uart_tx(USART_TypeDef *uart, uint8_t *data, int len)
{
    int i;

    for (i = 0; i < len; i++)
    {
        while ((uart->ISR & UART_FLAG_TXE) == 0);
        uart->TDR = (uint32_t)data[i];
    }
}
void main()
{
    boot_tag = "tag0\n";
    boot_uart_tx(hwp_usart1, (uint8_t *)boot_tag, strlen(boot_tag));
}