install_int_ex(3)               Allegro manual               install_int_ex(3)



NAME
       install_int_ex - Adds or modifies a timer. Allegro game programming
       library.

SYNOPSIS
       #include <allegro.h>


       int install_int_ex(void (*proc)(), int speed);

DESCRIPTION
       Adds a function to the list of user timer handlers or, if it is already
       installed, retroactively adjusts its speed (i.e makes as though the
       speed change occurred precisely at the last tick). The speed is given
       in hardware clock ticks, of which there are 1193181 a second. You can
       convert from other time formats to hardware clock ticks with the
       macros:

          SECS_TO_TIMER(secs)  - give the number of seconds between
                                 each tick
          MSEC_TO_TIMER(msec)  - give the number of milliseconds
                                 between ticks
          BPS_TO_TIMER(bps)    - give the number of ticks each second
          BPM_TO_TIMER(bpm)    - give the number of ticks per minute

       There can only be sixteen timers in use at a time, and some other parts
       of Allegro (the GUI code, the mouse pointer display routines, rest(),
       the FLI player, and the MIDI player) need to install handlers of their
       own, so you should avoid using too many at the same time. If you call
       this routine without having first installed the timer module,
       install_timer() will be called automatically.

       Your function will be called by the Allegro interrupt handler and not
       directly by the processor, so it can be a normal C function and does
       not need a special wrapper. You should be aware, however, that it will
       be called in an interrupt context, which imposes a lot of restrictions
       on what you can do in it. It should not use large amounts of stack, it
       must not make any calls to the operating system, use C library
       functions, or contain any floating point code, and it must execute very
       quickly. Don't try to do lots of complicated code in a timer handler:
       as a general rule you should just set some flags and respond to these
       later in your main control loop.

       In a DOS protected mode environment like DJGPP, memory is virtualised
       and can be swapped to disk. Due to the non-reentrancy of DOS, if a disk
       swap occurs inside an interrupt handler the system will die a painful
       death, so you need to make sure you lock all the memory (both code and
       data) that is touched inside timer routines. Allegro will lock
       everything it uses, but you are responsible for locking your handler
       functions. The macros LOCK_VARIABLE (variable), END_OF_FUNCTION
       (function_name), END_OF_STATIC_FUNCTION (function_name), and
       LOCK_FUNCTION (function_name) can be used to simplify this task. For
       example, if you want an interrupt handler that increments a counter
       variable, you should write:

          volatile int counter;

          void my_timer_handler()
          {
             counter++;
          }

          END_OF_FUNCTION(my_timer_handler)

       and in your initialisation code you should lock the memory:

          LOCK_VARIABLE(counter);
          LOCK_FUNCTION(my_timer_handler);

       Obviously this can get awkward if you use complicated data structures
       and call other functions from within your handler, so you should try to
       keep your interrupt routines as simple as possible.

RETURN VALUE
       Returns zero on success, or a negative number if there is no room to
       add a new user timer.


SEE ALSO
       install_timer(3), remove_int(3), install_int(3),
       install_param_int_ex(3), excamera(3), exsprite(3), extimer(3),
       exunicod(3), exupdate(3)



Allegro                          version 4.2.3               install_int_ex(3)
