why this progam in RTOS not running?

My guess is that the function os_start_system() in RTX51 does a similar thing as the os_sys_init() function in the ARM version of RTX.

The manual says "The os_sys_init function does not return."

If you let main() return, then it is up to the startup code to decide what will happen - if main will be restarted, the processor will be reset (leading to main being called again), the program getting stuck in an infinite loop after end of main(), ...

In short - consider it undefined behaviour what happens if you leave mai(), and make sure that it doesn't happen.

My guess is that the function os_start_system() in RTX51 does a similar thing as the os_sys_init() function in the ARM version of RTX.

The manual says "The os_sys_init function does not return."

If you let main() return, then it is up to the startup code to decide what will happen - if main will be restarted, the processor will be reset (leading to main being called again), the program getting stuck in an infinite loop after end of main(), ...

In short - consider it undefined behaviour what happens if you leave mai(), and make sure that it doesn't happen.

If you leave out the forever loop in main then Keil will insert a LJMP to 'Main'at the end of Main. That is why your main continues forever. As was pointed out, you should not have a 'Main' when using RTX51. RTX51 always enters at Task 0.
The Delete of the Task Startup code is a good practice. Normally you would have you system power up or reset initialization code in this task, then start your other tasks and then delete the Start up task. You don't want to re-run the initialization task again.
I don't see where you define P2_3 as any set bit code.
P2 is defined in the header but P2^3 is used to toggle the port bit.
Do you have a definition that I missed?
Bradford

Thanks for your help!
But I see the examples in RTX51.pdf, all of them use main() function. So I don't understand how to leave main(). Could you tell me a example without main() function?

What is the result of the following:

#include <rtx51.h>
#include <stdio.h>
#include <math.h>
#include <REGX51.H>

void  task1(void) _task_ 1 _priority_ 1 {
    while (1) {
        P2_1 = 0;
        os_wait(K_TMO,100,0);
    }
}

void  task2(void) _task_ 2 {
    while (1) {
        P2_1 = 1;
        os_wait(K_TMO,100,0);
    }
}

void start(void) _task_ 0 {
    os_set_slice(10000);
    os_create_task(1);
    os_create_task(2);
    P1 = 0;
    os_delete_task(os_running_task_id());
}

void  main(void) {
    P2_3 = 0;
    os_start_system(0);
}

Here is a quick modified code from the RTXTiny Example file.
Bradford

#include <rtx51tny.h>
#include <reg51.h>

sbit  Toggle = P2^1;

/*****************************************************/
/* Task 0 'job0': RTX-51 tiny starts execution with task 0             */
/**************************************************/
void start (void) _task_ 0
{       os_create_task (1);
        os_create_task (2);
        os_delete_task (os_running_task_id ());
}



/****************************************************/
/*   Task 1 'job1':  RTX-51 tiny starts this task with os_create_task (1)     */
/***********************************************/

void  task1 (void) _task_ 1
{
 while(1){
 Toggle = 0;
 os_wait(K_TMO, 100, 0);
 }
}


/****************************************************/
/*    Task 2 'job2':  RTX-51 tiny starts this task with os_create_task (2)    */
/****************************************************/
void  task2 (void) _task_ 2
{
 while(1){
 Toggle = 1;
 os_wait(K_TMO, 100, 0);
 }
}

Thank you very much for your code. I compile it with RTX-51 Tiny. It run successfull. I see the change state on P2_1.

Now I need to add the priority to the tasks. It means each task has different prioritys. And the program must use RTX-51 Full. From your code , I add the priority and compile with RTX-51 full. It's ok. But when I make simulation this program, I don't see any change state o P2_1. So I sets the same priority to task 1 and 2 . But that has no effect.

This is the code:

#include <rtx51tny.h>
#include <reg51.h>

sbit  Toggle = P2^1;

/*****************************************************/
/* Task 0 'job0': RTX-51 tiny starts execution with task 0             */
/**************************************************/
void start (void) _task_ 0
{       os_create_task (1);
        os_create_task (2);
        os_delete_task (os_running_task_id ());
}

/****************************************************/
/*   Task 1 'job1':  RTX-51 tiny starts this task with os_create_task (1)     */
/***********************************************/

void  task1 (void) _task_ 1 _priority_ 1
{
 while(1){
 Toggle = 0;
 os_wait(K_TMO, 10, 0);
 }
}

/****************************************************/
/*    Task 2 'job2':  RTX-51 tiny starts this task with os_create_task (2)    */
/****************************************************/
void  task2 (void) _task_ 2 _priority_ 1
{
 while(1){
 Toggle = 1;
 os_wait(K_TMO, 10, 0);
 }
}

Could you give me advice?
Thanks a lot!

Glad you have your first RTX Tiny running. I'm sorry but I do not have RTX Full on this computer so I do not have the documentation but have you added the correct header files for RTX Full? Have you selected the correct operating system under Targets -> Operating system? This will load the correct library files.
That's about all I can remember of RTX Full without the documentation available to me at this time.
Bradford