ZYNQ 串口持續觸發 TX FIFO EMPTY中斷 XUARTPS_IXR_TXEMPTY

1.ZYNQ 串口持續觸發 TX FIFO EMPTY中斷（XUARTPS_IXR_TXEMPTY）

問題描述：

? ZYNQ 7020 串口作業為中斷觸發模式，使用XUartPs_Send()函式發送完成資料之后，會產生一個 TX FIFO EMPTY中斷（盡管串口初始化中斷時并沒有使能XUARTPS_IXR_TXEMPTY中斷），同時會呼叫串口中斷處理函式，如果沒有清除處中斷標志位，除非關閉中斷XScuGic_Disable()否則會持續呼叫中斷處理函式，影響程式正常運行，

產生原因：

? 呼叫XUartPs_Send()函式時，會先關閉TX EMPTY和TX FULL中斷

	/*
	 * Disable the UART transmit interrupts to allow this call to stop a
	 * previous operation that may be interrupt driven.
	 */
	XUartPs_WriteReg(InstancePtr->Config.BaseAddress, XUARTPS_IDR_OFFSET,
					  (XUARTPS_IXR_TXEMPTY | XUARTPS_IXR_TXFULL));

     BytesSent = XUartPs_SendBuffer(InstancePtr);

? 然后呼叫XUartPs_SendBuffer()函式，在該函式中，如果開啟了接收中斷，則會開啟TX EMPTY的中斷，

/*
	 * If interrupts are enabled as indicated by the receive interrupt, then
	 * enable the TX FIFO empty interrupt, so further action can be taken
	 * for this sending.
	 */
	ImrRegister =
		XUartPs_ReadReg(InstancePtr->Config.BaseAddress,
				  XUARTPS_IMR_OFFSET);
	if (((ImrRegister & XUARTPS_IXR_RXFULL) != (u32)0) ||
		((ImrRegister & XUARTPS_IXR_RXEMPTY) != (u32)0)||
		((ImrRegister & XUARTPS_IXR_RXOVR) != (u32)0)) {

		XUartPs_WriteReg(InstancePtr->Config.BaseAddress,
					   XUARTPS_IER_OFFSET,
					   ImrRegister | (u32)XUARTPS_IXR_TXEMPTY);//使能TX EMPTY中斷
	}

解決辦法：

（1）在中斷處理函式中對發送FIFO中斷進行判斷，如果觸發該中斷，則清除中斷標志，

（2）使用XUartPs_SendByte()按位元組發送資料，

串口發送代碼：

void Ublox_Cfg(u8 type)
{
	switch(type)
	{
		case Hot:
		{
			unsigned char uart_send[] ={0xB5, 0x62, 0x06, 0x04, 0x04, 0x00, 0x00, 0x00, 0x02, 0x00, 0x10, 0x68};
			XUartPs_Send(&Uart_Ps, uart_send, 12);
			break;
		}
		default:
			break;
	}
}

中斷處理函式代碼：

void uart_handler(void *call_back_ref)
{
	XUartPs *uart_instance_ptr = (XUartPs *) call_back_ref;
	u32 IsrStatus;
	u32 rx_realnumber;
	//讀取中斷 ID 暫存器，判斷觸發的是哪種中斷
	IsrStatus = XUartPs_ReadReg(uart_instance_ptr->Config.BaseAddress,
	XUARTPS_IMR_OFFSET);
	IsrStatus &= XUartPs_ReadReg(uart_instance_ptr->Config.BaseAddress,
	XUARTPS_ISR_OFFSET);
	if((IsrStatus & (u32)XUARTPS_IXR_TXEMPTY))
	{
		XUartPs_WriteReg(uart_instance_ptr->Config.BaseAddress, XUARTPS_ISR_OFFSET, XUARTPS_IXR_TXEMPTY) ;//clear TX FIFO中斷
	}
	if((IsrStatus & (u32)XUARTPS_IXR_RXOVR))//接收FIFO觸發中斷
	{
		rx_realnumber = XUartPs_Recv(uart_instance_ptr,&uart_recv[uart_totalnumber],512);//讀取FIFO資料到陣列，回傳實際接收長度
		uart_totalnumber += rx_realnumber;//計算總接收長度
		XUartPs_WriteReg(uart_instance_ptr->Config.BaseAddress, XUARTPS_ISR_OFFSET, XUARTPS_IXR_RXOVR) ;//clear 中斷
	}
}

串口初始化代碼：

int uartps_init(XUartPs* uart_ps)
{
	int status;
	XUartPs_Config *uart_cfg;
	XScuGic_Config *intc_cfg;
	uart_cfg = XUartPs_LookupConfig(UART_DEVICE_ID);
	if (NULL == uart_cfg)
		return XST_FAILURE;
	status = XUartPs_CfgInitialize(uart_ps, uart_cfg, uart_cfg->BaseAddress);
	if (status != XST_SUCCESS)
		return XST_FAILURE;

	XUartPs_SetOperMode(uart_ps, XUARTPS_OPER_MODE_NORMAL);
	XUartPs_SetBaudRate(uart_ps,UART_BAUD);
	XUartPs_SetFifoThreshold(uart_ps,60);
    
	Xil_ExceptionInit();
	intc_cfg = XScuGic_LookupConfig(INTC_DEVICE_ID);
	if (NULL == intc_cfg)
		return XST_FAILURE;
	status = XScuGic_CfgInitialize(&Intc, intc_cfg,intc_cfg->CpuBaseAddress);
	if (status != XST_SUCCESS)
		return XST_FAILURE;
	Xil_ExceptionRegisterHandler(XIL_EXCEPTION_ID_IRQ_INT,(Xil_ExceptionHandler)XScuGic_InterruptHandler,(void *)&Intc);
	XScuGic_Connect(&Intc,UART_INT_IRQ_ID,(Xil_ExceptionHandler)uart_handler,(void *)uart_ps);
	//設定 UART 的中斷觸發方式
	XUartPs_SetInterruptMask(uart_ps,XUARTPS_IXR_RXOVR); //此處沒有打開XUARTPS_IXR_TXEMPTY中斷
	Xil_ExceptionEnable();
	XScuGic_Enable(&Intc,UART_INT_IRQ_ID);
	return XST_SUCCESS;
}