' *********** CHNEVENT.BAS *******************************************

      DEFINT A-Z

      DECLARE FUNCTION InstallHandler% (BYVAL InterruptNumber%)

' This MASM function attempts to install our service routine,
' returning -1 if it could not do so (zero if OK).  The parameter
' InterruptNumber can range from 0-255, but for the sake of your
' sanity, please don't try it indiscriminately... there *are* some
' vectors which will cause crashes (at a minimum).
'
' Contrast this with the InstallHandler in the HDWEVENT package, which
' is passed an IRQ number from 2-7, not a vector number from 0 to 255.
'
' NOTE that this CANNOT be called multiple times to install multiple
' handlers!

      ON UEVENT GOSUB MyEventHandler   'establish a handler
      UEVENT ON                        'activate handler

      IF InstallHandler(9) THEN
         PRINT "Could not install interrupt handler"
         STOP
      END IF

' The following is just a way to get INT 9's to occur.  Whatever you
' type will be echoed onto the screen, and each press, release, or
' repeat of a key will invoke MyEventHandler, causing a click sound.

      DO
         k$ = INKEY$
         IF k$ = CHR$(27) THEN
           EXIT DO
         END IF
         PRINT k$;
      LOOP
      SYSTEM

MyEventHandler: 'just make a ticking noise when the event is detected

      SOUND 2000, .1    'make a small noise
      RETURN