Not jumping to ISR

I'm working on developing interrupt driven comms for an lpc2129 and having a problem getting the interrupts working. It all seemed fairly straight forward so I must be missing something. What I have is a short main loop that will echo back any Rx'd bytes on uart1. This works fine until I enable the interrupts for uart1 at which point something goes amuk.

The ISR for uart1 is going to echo the rx'd byte back out the port - simple enough to get started with. When I enable uart1 interrupts and single step via the debugger, I can see the Receive Data Ready interrupt bit get set when I send the uart a character. However, flow continues normally - that is, no jump is made to the ISR. The character I send is then echoed back via the code in the main loop (NOT the ISR).

When I run the code without the debugger I get nothing back from the board via uart1 so I'm assuming I'm getting hung up someplace.

This is the main loop:

while(1)  {
		if( getchar_uart1() )
			putchar_uart1( cTemp );   /* echo any bytes Rx'd */
}

This is the getchar function:

int getchar_uart1( void )  {
	if( U1LSR & 0x01 )   /* if data return it */
		return (U1RBR);
	else
		return 0;
}/* end getchar_uart1 */

The following snippet is the setup code for uart1:

void init_uart1( void )  {
	PINSEL0 |= 0x00550000;   /* set P0.8, P0.9, P0.10 and P0.11 as TxD1, RxD1, RTS1, CTS1 */
	U1LCR = 0x83;   /* set DLAB and word size (8bits), defaults for others yield */
						 /* no parity, one stop bit, and no break */
	U1DLL = 0x61;   /* yields 9600 Baud */
	U1DLM = 0x00;   /* explicit initialization - is also the default */
	U1LCR &= 0x7f;   /* clear DLAB */

/* set up the interrupts */
	U1IER = 0x05;   /* enable RDA and THRE interrupts */
	VICVectAddr1 = (unsigned long) u1_interrupt;   /* set interrupt vector */
	VICVectCntl1 = 0x20 | 7;   /* use VICVectAddr1 for UART1 interrupts */
	VICIntEnable = 0x00000080;   /* enable uart1 interrupts */

}/* end init_uart1() */

and this is the ISR:

void u1_interrupt (void) __attribute__ ((interrupt));   /* generate interrupt */

/*************************************************************************/
/**************************  interrupt for uart1  ************************/
void u1_interrupt (void)  {
	if( U1IIR && U1LSR &= 0x20 ) /* Tx buffer empty? - also clearing U1IIR */
		U1THR = U1RBR;   /* echo the Rx'd byte */
	VICVectAddr = 0;   /* acknowledge interrupt */
}/*end u1_interrupt() */

As I said, when using the debugger and a byte is Rx'd code flow in the getchar_uart1() contiues instead of the ISR. I can see the interrupt triggered in the uart1 peripheral window and the VIC window is also correct (intEnabled for uart1, type IRQ 1).

Any suggestions/solutions appreciated.
-m