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HC32F460串口波特率设置19200，函数返回ErrorInvalidParameter

发布时间 2023-08-01 17:32:37作者: lazy12138

今天，在调试项目的时候，遇到设置串口2波特率为19200的时候，USART_SetBaudrate(M4_USART2, 19200)函数返回 ErrorInvalidParameter，导致程序陷入了死循环，配置程序如下：

void USART2_LIN_Config(void){
    
#ifdef LIN_EN
 #ifdef HC32_MCU
   stc_usart_uart_init_t stcInitCfg;
     en_result_t enRet;
     
     stcInitCfg.enClkDiv = UsartClkDiv_1;
     stcInitCfg.enClkMode = UsartIntClkCkNoOutput;
     stcInitCfg.enDataLength = UsartDataBits8;
     stcInitCfg.enDirection = UsartDataLsbFirst;
     stcInitCfg.enStopBit = UsartOneStopBit;
     stcInitCfg.enParity = UsartParityNone;
     stcInitCfg.enSampleMode = UsartSamleBit8;
     stcInitCfg.enDetectMode = UsartStartBitFallEdge;
     stcInitCfg.enHwFlow = UsartRtsEnable;
     enRet = USART_UART_Init(M4_USART2, &stcInitCfg);
     if (enRet != Ok)
        { while (1); }
     enRet = USART_SetBaudrate(M4_USART2, 19200);
     if (enRet != Ok)
        { while (1); }
     USART_FuncCmd(M4_USART2, UsartRx, Enable);
   USART_FuncCmd(M4_USART2, UsartTx, Enable);
     USART_FuncCmd(M4_USART2, UsartRxInt,Enable);
 #endif
#endif
}

之后，我百思不得其解，根据函数注释来看是“ErrorInvalidParameter       USARTx is invalid”，也就是串口无效，这怎么可能呢，之后我进入底层函数查看

在   static en_result_t SetUartBaudrate(M4_USART_TypeDef *USARTx, uint32_t u32Baudrate)  函数里看，

DIV = ((float)C / ((float)B * 8.0f * (2.0f - (float)OVER8))) - 1.0f;
            DIV_Integer = (uint32_t)(DIV);

            if (!((DIV < 0.0f) || (DIV_Integer > 0xFFul)))
            {
                enRet = Ok;
                if ((DIV - (float32_t)DIV_Integer) > 0.00001f)
                {
                    /* FBME = 1 Calculation formula */
                    /* B = C * (128 + DIV_Fraction) / (8 * (2 - OVER8) * (DIV_Integer + 1) * 256) */
                    /* DIV_Fraction = ((8 * (2 - OVER8) * (DIV_Integer + 1) * 256 * B) / C) - 128 */
                    /* E = (C * (128 + DIV_Fraction) / (8 * (2 - OVER8) * (DIV_Integer + 1) * 256 * B)) - 1 */
                    /* DIV_Fraction = (((2 - OVER8) * (DIV_Integer + 1) * 2048 * B) / C) - 128 */
                    u64Tmp = (uint64_t)(((uint64_t)2ul - (uint64_t)OVER8) * ((uint64_t)DIV_Integer + 1ul) * (uint64_t)B);
                    DIV_Fraction = (uint32_t)(2048ul * u64Tmp / C - 128ul);
                    if (DIV_Fraction > 0x7Ful)
                    {
                        enRet = ErrorInvalidParameter;
                    }
                }

                if (Ok == enRet)
                {
                    USARTx->CR1_f.FBME = (DIV_Fraction > 0x7Ful) ? 0ul : 1ul;
                    USARTx->BRR_f.DIV_FRACTION = DIV_Fraction;
                    USARTx->BRR_f.DIV_INTEGER = DIV_Integer;
                }
            }

我怀疑是频率的问题，原先给串口分配的频率是42MHz，之后我改为10.5MHz，就好了