the number of tasks

Jian,

I don't use the Arm compiler, so what follows is unlikely to work for you, however here we go:
- the debugger can tell you right away how many tasks are running, plus much more information. It should be part of the "peripherals" menu.
- if you want your own program to know how many tasks are running, a good place to start looking is os_active_TCB[].

I imagine that a piece of code like:

    #include "blah...\AR166\SRC\Kernel\AR166_Config.h"
    #include "blah...\AR166\SRC\Kernel\AR_C_Interface.h"
    unsigned int NumberOfRunningTasks = 0;
    for (i=os_maxtaskrun; i--;)
    {
        if (os_active_TCB[i]!=PNULL)
        {
            NumberOfRunningTasks++;
        }
    }