an UART programme

Hi there,I'm trying to delievering and recieving charactors by UART:while I recieve a charactor(for example:0x00),I delieve 0x01.Below is my C programme,could anyone tell me if there's any problems ?Thank you!

# include <unistd.h># include <string.h># include "system.h"# include "sys/alt_irq.h"# include "altera_avalon_uart_regs.h"# include "alt_types.h"# include "altera_avalon_uart.h"# include "altera_avalon_uart_regs.h"# define RRDY_MSK 0x0080# define TRDY_MSK 0x0080

//ISR for receiving and delievering

static void uart_isr(void* context, alt_u32 id)

{

/*

* Read the status register in order to determine the cause of the

* interrupt.

*/

alt_u32 status;

alt_u8 rxdata;

status = IORD_ALTERA_AVALON_UART_STATUS(UART_0_BASE);

/* Clear any error flags set at the device */

IOWR_ALTERA_AVALON_UART_STATUS(UART_0_BASE, 0);

/* process a read irq */

if (status&ALTERA_AVALON_UART_STATUS_RRDY_MSK)

{

rxdata=IORD_ALTERA_AVALON_UART_RXDATA(UART_0_BASE);

}

/* process a write irq */

if (status&ALTERA_AVALON_UART_STATUS_TRDY_MSK)

{

IOWR_ALTERA_AVALON_UART_TXDATA(UART0_BASE, 0x01);

}

}

int main()

{

//enable the uart_0 interrupt

IOWR_ALTERA_AVALON_UART_CONTROL(UART_0_BASE,ALTERA_AVALON_UART_CONTROL_RRDY_MSK|

ALTERA_AVALON_UART_CONTROL_TRDY_MSK);

//Register the interrupt handler

alt_irq_register(UART_0_IRQ,0,uart_isr);

if(rxdata)

{

IOWR_ALTERA_AVALON_UART_TXDATA(UART0_BASE, 0x01);

}

return 0;

}