/* TIMER.H */
/* Routines for reprogramming of timer and Ctrl-Break */

/* User-defined routines */
void user_init();       /* Initialization program. Sets the frequency   */
void user_interface();  /* Interface task. Executed in the foreground   */     
void user_task();       /* Periodic task. Executed in the background    */
void user_terminate();  /* Termination task. Executed after terminate() */
void user_abort();      /* Abort task. Executed after ctrl-break        */

void newbreak_start(), newbreak_stop(),newtask_start();

/* Declaration of program variables */
/* freq is the sampling frequency (Hz) and must be set by the user */
float freq; int countdown,lobyte,hibyte,count,doscount,done;

/* Routines to change the interrupt rate of the timer */
/* and to redirect the timer processing */
void (interrupt *oldtask) ();
void interrupt newtask() {
	user_task();
	if ( count==0 ){(*oldtask)();count=doscount;}
	else{--count;outp(0x20,0x20); } }
void newtask_init() {
	countdown=(int)(1193180./freq);
	hibyte=(int)(countdown/256);
	lobyte=countdown-hibyte*256;
	count=done=0; doscount=(int)(freq/18.2); }      
void newtask_start() {
	disable();
	oldtask=getvect(0x08);
	outp(0x43,0x36); outp(0x40,lobyte); outp(0x40,hibyte); 
	setvect(0x08,newtask);
	enable(); }
void newtask_stop() {
	disable();
	setvect(0x08,oldtask);
	outp(0x43,0x36); outp(0x40,0); outp(0x40,0);
	enable(); }

/* Routines to redirect the Ctrl-Break processing */
void (interrupt *oldbreak) ();
void interrupt newbreak() {
	newtask_stop(); newbreak_stop(); outp(0x20,0x20);
	user_abort(); exit(1); }
void newbreak_start () {
	disable();
	oldbreak=getvect(0x23); setvect(0x23,newbreak);
	enable(); }
void newbreak_stop() {
	disable();
	setvect(0x23,oldbreak);
	enable(); }
void terminate() {
	newtask_stop(); newbreak_stop(); outp(0x20,0x20);
	user_terminate(); exit(1); }

/* Main program */
main() {
	user_init(); newtask_init();
	newbreak_start(); newtask_start();
	while(!done){user_interface();} }