| OSVRegisterTimer | Function* (tigcc.a)

system.h

short OSVRegisterTimer (short timer_no, unsigned long T, Timer_Callback_t Action);

Registers an event (vectored) timer.

Before release 2.04 of the AMS, TIOS also had two event (vectored) timers numbered as 1 and 2 (in addition to 6 notify timers which may be registered using OSRegisterTimer). In AMS 2.04, Texas Instruments decided for some strange reasons to remove these vectored timers from the TIOS. I was very angry due to this decision, so I decided to reimplement these timers independently of the TIOS, to make them work on any AMS version. Well, now you have it. More precise, you now have two event (vectored) timers which are numbered as 1 and 2, which work on any AMS release (TIOS based implementation as implemented in TIGCCLIB releases prior to 2.2 did not work on AMS 2.04 and AMS 2.05).
OSVRegisterTimer initializes the event timer which ID number is timer_no, and sets its initial value to T. Every time the Auto-Int 5 is triggered (20 times per second if you didn't change the programable rate generator), the current value of the timer is decremented by 1. When the current value reaches zero, a procedure specified by user will be called, then the timer starts counting again from its initial value. The parameter Action is the pointer to the procedure which will be triggered every time the timer reaches zero. So, the procedure Action will be called periodically, with a period determined by T.
Action need not to be an assembly language procedure; it may be any user-defined function written in C. Its body will be executed in the supervisor CPU mode and with disabled interrupts (th information is probably not important from the user point of view).
If the function Action changes any global variable in the program, such global variable must be declared as "volatile" to inform the compiler that its value may be changed asynchronously, i.e. in a way which is unexpected for the normal program flow.
OSVRegisterTimer returns a nonzero value if the registration was successful, else returns zero. This happens if you give wrong parameters, or if the timer timer_no is already in use. So, you must first free the timer using OSVFreeTimer (as I completely rewrote these routines, I also corrected some bugs in them which were presented in TIOS routines; you know about them if you read the documentation about OSVRegisterTimer in earlier releases of TIGCCLIB). As event timers now work indepentently of TIOS timers, both event timers (1 and 2) are free for use. Here is a simple example of a program which installs both event timers (called "Timers"):

    // Install two timers with counter variables

    #define USE_TI89              // Compile for TI-89
    #define USE_TI92PLUS          // Compile for TI-92 Plus
    #define USE_V200              // Compile for V200

    #define MIN_AMS 100           // Compile for AMS 1.00 or higher
    #define SAVE_SCREEN           // Save/Restore LCD Contents

    #include <tigcclib.h>         // Include All Header Files

    CALLBACK void Action1(void)
    {
      static int Counter = 0;
      printf_xy (50, 50, "Counter1 = %d  ", ++Counter);
    }

    CALLBACK void Action2(void)
    {
      static int Counter = 0;
      printf_xy (70, 70, "Counter2 = %d  ", ++Counter);
    }

    void _main(void)
    {
      OSVRegisterTimer (1, 3, Action1);
      OSVRegisterTimer (2, 10, Action2);
      ngetchx ();
      OSVFreeTimer (1);
      OSVFreeTimer (2);
    }

In this implementation of OSVRegisterTimer, it is not necessary to free timers using OSVFreeTimer before first usage of them, because they are free by default at the begining. However, nothing wrong will happen if you try to free them explicitely (which was necessary in previous releases of TIGCCLIB).
Note: As already mentioned above, all TIOS bugs in timer routines (dependence between notify and event timers, etc.) are now removed, because these routines are rewritten to be independent of the TIOS.