中断的添加过程：

首先，因为中断要调用上下文切换代码，所以用汇编语言入口。

再从汇编语言中调用C语言。　需然在中断程序中不会完成多少任务，但是用C毕竟简化了工作，并给了代码充分的可读性。

最后就是将中断向量写入AIC的中断向寄存器了。

中断程序：

汇编部分：

RSEG ICODE:CODE
CODE32

EXTERN vUARTISR
PUBLIC vUARTISREntry

; Wrapper for the EMAC interrupt service routine. This can cause a
; context switch so requires an assembly wrapper.

; Defines the portSAVE_CONTEXT and portRESTORE_CONTEXT macros.

#include "ISR_Support.h"

vUARTISREntry:

portSAVE_CONTEXT ; Save the context of the current task.

bl vUARTISR ; Call the ISR routine.

portRESTORE_CONTEXT ; Restore the context of the current task -
; which may be different to the task that
; was interrupted.

END

C语言部分：

__arm void vUARTISR( void )
{
unsigned int status;
int i;

status = AT91C_BASE_US0->US_CSR;
AT91C_BASE_US0->US_CR = AT91C_US_RSTSTA;

if( status & AT91C_US_ENDRX )
{
for( i = 0; i < Rx_Count; i )
{
US0_BuffTx[ i ] = US0_BuffRx[ i ];
}

Tx_Count = Rx_Count;
AT91C_BASE_US0->US_TPR = ( unsigned int )US0_BuffTx;
AT91C_BASE_US0->US_TCR = ( unsigned int )Tx_Count;

AT91C_BASE_US0->US_RPR = (unsigned int )US0_BuffRx;
Rx_Count = 8;
AT91C_BASE_US0->US_RCR = Rx_Count;
}
else if( status & AT91C_US_ENDTX )
{

}
else
{
AT91C_BASE_US0->US_THR = 'C';
}

//中断结束之后要通知系统中断处理完毕，否则下次此器件将不会产生中断
AT91C_BASE_AIC->AIC_EOICR = 0x1234;

}

其中有一部分是在外面定义的全局变量。

unsigned int US0_BuffRx[256];
int Rx_Count;
unsigned int US0_BuffTx[256];
int Tx_Count;

中断设置部分：

/*-----------------------------------------------------------*/
void Init_UART_DMA()
{
AT91PS_PIO pIO = AT91C_BASE_PIOA;
pIO->PIO_PDR |= 0x03;
pIO->PIO_ASR |= 0x03;

AT91C_BASE_PMC->PMC_PCER |= ( 1 << AT91C_ID_US0 );
//USART :Normal Mode
//USCLKS:MCK
//CHRL(CHARACTER LENGTH):8BIT(11)
//SYNC:0 In Asynchronous Mode
//PAR:(100) No Parity
//NBSTOP:1 stop bit
//CHMODE(CHANNEL MODE):Normal Mode
AT91C_BASE_US0->US_MR = 0x08C0;

//baudrate = Select_Clock/(8(2-over)CD) = 47923200/(16*312) = 9600
AT91C_BASE_US0->US_BRGR = 312;

//reset usart0
AT91C_BASE_US0->US_CR = 0x010C;
//set interrupt bit
AT91C_BASE_US0->US_IDR = 0xFFFFF;
//enable rxen and txen
AT91C_BASE_US0->US_CR = 0x0050;
//Disable AIC interrupt
AT91F_AIC_DisableIt( AT91C_BASE_AIC, AT91C_ID_US0 );
//Enable Interrupt in us0
AT91C_BASE_US0->US_IER = 0x00018;

AT91F_DBGU_Print32( AT91C_BASE_US0->US_CSR );

AT91C_BASE_US0->US_PTCR = 0x00000101;

prvSetupUARTInterrupt( );

AT91C_BASE_US0->US_RPR = ( unsigned int )US0_BuffRx;
Rx_Count = 8;
AT91C_BASE_US0->US_RCR = Rx_Count;

}
/*-----------------------------------------------------------*/

static void prvSetupUARTInterrupt( void )
{
/* Enable the interrupts in the AIC. */
AT91F_AIC_ConfigureIt(

AT91C_BASE_AIC,

AT91C_ID_US0, 6,

AT91C_AIC_SRCTYPE_INT_HIGH_LEVEL,

( void (*)( void ) ) vUARTISREntry

);

AT91F_AIC_EnableIt( AT91C_BASE_AIC, AT91C_ID_US0 );

}