stuart interrupt problem on pxa255 board

Hi, i'm developing a bootloader on a pxa255 based board.
I have a problem using stuart RX interrupt.
When I enter a character on a console, it receives the correct
character when I read the STRBR register, but no jump to my IRQ
function.

Below is a function initializing stuart.
void serial_init(unsigned long baudrate)
{
        unsigned int rate;


        rate = UART_CLOCK/(16*baudrate);


        _bl_disable_irq();


        CKEN |= CKEN5_STUART;


        STFCR = 0;  /* disable TX/RX FIFO */


        /* set baud rate */
        STLCR = LCR_DLAB; /* DLAB on */
        STDLL = rate & 0xFF;
        STDLH = rate >> 8;
        STLCR = LCR_WLS0 | LCR_WLS1;


                 /* enable and reset TX/RX FIFO(1-byte rx threshold
FIFO) */
        STFCR |= FCR_TRFIFOE|FCR_RESETRF|FCR_RESETTF;


        __asm{ nop }
        STLCR &= ~LCR_DLAB; /* DLAB off */
        STIER = IER_UUE | IER_RAVIE; /* enable UART, RX interrupt */


        ICMR = 0xFFFFFFFF;


               _bl_enable_irq();



}


Below is the hexadecimal register values I print
when a character is received(STLSR & LSR_DR).
STIER=41, STLSR=21, STIIR=c4, ICIP=0, ICMR=ffffff80, ICPR=0
[
  STIER=41 => 0x40:uart enabled,
                       0x01:Receiver Data Available Interrupt Enable.
  STLSR=21 => 0x20:Transmit FIFO has half or less than half data,
                       0x01:Data is available in RBR or the FIFO
  STIIR=c4 => 0xc0:FIFO mode is selected
                     0x04:Received Data Available
  ICIP=0 => IRQ Pending Register
  ICMR=FFFFFF80
  ICPR=0 => no interrupt pending (why ?????????)
]

Below is the part I print above register values.
(void)itoa(rcv_char, buffer, 16);
serial_puts("\r\nc started, cpsr=");
serial_puts(buffer);
serial_puts(", STIER=");
rcv_char = STIER;
(void)itoa(rcv_char, buffer, 16);
serial_puts(buffer);
serial_puts(", ICMR=");
rcv_char = ICMR;
(void)itoa(rcv_char, buffer, 16);
serial_puts(buffer);
serial_puts("\r\n\n");


while(1) {
    if(STLSR & LSR_DR) {
        serial_puts("STIER=");
        rcv_char = STIER;
        (void)itoa(rcv_char, buffer, 16);
        serial_puts(buffer);


        serial_puts(", STLSR=");
        rcv_char = STLSR;
        (void)itoa(rcv_char, buffer, 16);
        serial_puts(buffer);


        serial_puts(", STIIR=");
        rcv_char = STIIR;
        (void)itoa(rcv_char, buffer, 16);
        serial_puts(buffer);


                serial_puts(", ICIP=");
        rcv_char = ICIP;
        (void)itoa(rcv_char, buffer, 16);
        serial_puts(buffer);


        serial_puts(", ICMR=");
        rcv_char = ICMR;
        (void)itoa(rcv_char, buffer, 16);
        serial_puts(buffer);


        serial_puts(", ICPR=");
        rcv_char = ICPR;
        (void)itoa(rcv_char, buffer, 16);
        serial_puts(buffer);


        //serial_puts(", char=");
        //rcv_char = serial_tstc();
        //serial_putc((char)rcv_char);
        serial_puts("\r\n");
        rcv_char = STRBR;
    }



}


The global interrupt in CPSR is enabled.
And when I tested using OS timer, the coresponding interrupt was
generated correctly.

Any help will be greatly appreciated. 
Thanks. 
Terry.