usart0_isr.c

UART developing tutorial module with source codes a褌胁 hints.

//  *****************************************************************************
//   						usart0_isr.c
// 
//     USART0 Interrupt Service Routine
//
//	   This demonstration is designed to read 10 characters into a buffer.
//     After the 10th character arrives, transmit the 10 characters back.
//
//	   The application is interrupt-driven.
//
//  Author:  James P Lynch  June 22, 2008
//  ***************************************************************************** 

//  *******************************************************
//                Header Files
//  *******************************************************
#include "at91sam7x256.h"
#include "board.h"

//  *******************************************************
//                Global Variables
//  *******************************************************
char			Buffer[32];				// holds received characters
unsigned long	nChars = 0;				// counts number of received chars
char			*pBuffer = &Buffer[0];	// pointer into Buffer


void Usart0IrqHandler (void) {
         
	volatile AT91PS_USART pUsart0 = AT91C_BASE_US0;		// create a pointer to USART0 structure
	
	// determine which interrupt has occurred 
	// assume half-duplex operation here, only one interrupt type at a time
	if ((pUsart0->US_CSR & AT91C_US_RXRDY) == AT91C_US_RXRDY) {

		// we have a receive interrupt, 
		// remove it from Receiver Holding Register and place into buffer[]
		*pBuffer++ = pUsart0->US_RHR;
		nChars++;
		
		// check if 10 characters have been received
		if (nChars >= 10) {
			
			// yes, redirect buffer pointer to beginning
			pBuffer = &Buffer[0];
			nChars = 0;
			
			// disable the receive interrupt, enable the transmit interrupt
			pUsart0->US_IER = AT91C_US_TXEMPTY;					// enable TXEMPTY usart0 transmit interrupt
			pUsart0->US_IDR = ~AT91C_US_TXEMPTY;				// disable all interrupts except TXEMPTY
			
			// send first received character, TXEMPTY interrupt will send the rest
			pUsart0->US_THR = *pBuffer++;
			nChars++;
		}
		
	} else if ((pUsart0->US_CSR & AT91C_US_TXEMPTY) == AT91C_US_TXEMPTY) {
		
		// we have a transmit interrupt (previous char has clocked out)
		// check if 10 characters have been transmitted
		if (nChars >= 10 ) {
			
			// yes, redirect buffer pointer to beginning
			pBuffer = &Buffer[0];
			nChars = 0;
			
			// enable receive interrupt, disable the transmit interrupt
			pUsart0->US_IER = AT91C_US_RXRDY;					// enable RXRDY usart0 receive interrupt
			pUsart0->US_IDR = ~AT91C_US_RXRDY;					// disable all interrupts except RXRDY
			
		} else {
			
			// no, send next character
			pUsart0->US_THR = *pBuffer++;
			nChars++;
		}
	}
}