void hw_uart4_init(u32 band)

{

? ? GPIO_InitTypeDef GPIO_InitStructure = { 0 };

? ? USART_InitTypeDef USART_InitStructure = { 0 };

? ? NVIC_InitTypeDef NVIC_InitStructure = { 0 };

? ? RCC_APB1PeriphClockCmd( RCC_APB1Periph_USART4, ENABLE );

? ? RCC_APB2PeriphClockCmd( RCC_APB2Periph_GPIOA, ENABLE );

? ? USART_DeInit(USART4);

? ? GPIO_InitStructure.GPIO_Pin = GPIO_Pin_5;

? ? GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;

? ? GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF_PP;

? ? GPIO_Init( GPIOA, &GPIO_InitStructure );

? ? GPIO_PinRemapConfig(GPIO_PartialRemap1_USART4, ENABLE);

? ? USART_InitStructure.USART_BaudRate = baund;

? ? USART_InitStructure.USART_WordLength = USART_WordLength_8b;

? ? USART_InitStructure.USART_StopBits = USART_StopBits_1;

? ? USART_InitStructure.USART_Parity = USART_Parity_No;

? ? USART_InitStructure.USART_HardwareFlowControl = USART_HardwareFlowControl_None;

? ? USART_InitStructure.USART_Mode = USART_Mode_Tx | USART_Mode_Tx;

? ? USART_Init( USART4, &USART_InitStructure );

? ? USART_Cmd( USART4, ENABLE );

}

void hw_uart4_send_bytes(u8 *xbuf, u16 slen)

{

? ? ?u16 i;

? ? ?for(i = 0; i < slen; i++)

? ? ?{

? ? ? ? ?while(USART_GetFlagStatus(USART4, USART_FLAG_TC) == RESET);

? ? ? ? ?USART_SendData(USART4, xbuf[i]);

? ? ?}

}

?uart4初始化和發(fā)送函數(shù)如上，hw_uart4_send_bytes發(fā)送數(shù)據(jù)，PA5沒(méi)任何波形輸出，芯片為CH32X033F8P6。

使用PA5作為UART4的TX引腳需要做端口重映射映射，看你的程序，沒(méi)有打開(kāi)AFIO時(shí)鐘，同時(shí)端口重映射的函數(shù)要在GPIO初始化之前調(diào)用才能有效。