Problem about multi-task in RL-RTX

Hi all,
I want to implement UDP communication between two LPC1768 boards. Coz each board should be able to send msg as well as receive msg at the same time, the only way I thought about is multi-task under RTOS.

I use the RL-RTX and create two tasks. The problem is if I only do some simply stuff in the task, like display a char on the screen, then it works fine. But if I add more in the task, it will stuck somewhere in the while loop.

I tried on one example, Keil\ARM\Boards\Keil\MCB1700\RL\TCPnet\LEDClient, i put the send function into a task. But the code stuck when the 2nd time it starts the while loop. (i use the display function to see the code step) I don't know the reason. Do I miss some key configuration?

__task void send_msg(void)
{
  U8 p2val, cnt, lshf;
  p2val = 1;
  cnt   = 0;
  lshf  = 1;  /* left shift */
  while (1) {
  timer_poll();
  main_TcpNet ();
  while (1) {
  if (tick == __TRUE) {
    if (++cnt == 2) {
        LED_out (p2val);
        send_data(p2val);
        p2val = lshf ? (p2val << 1) : (p2val >> 1);
        if (p2val == 0x80) lshf = 0;
        if (p2val == 0x01) lshf = 1;
        cnt = 0;
    }
    tick = __FALSE;
  }
  }
}

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well...I changed the priviledged mode in RTX_Config, set OS_RUNPRIV to 1. Then it seems all right...I am not totally understand it right now, I'm quite a rookie in embedded sys...

Another thing is the stack setting in config file. I find there're two places to set stack size. One in startup_LPC17xx.s Stack_Size and another in RTX_Config.c OS_STKSIZE...I don't really know how to properly set it...

Thanks all.
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