/* Measure period of pulse at IC1. 
   Error: +/- 100ms (0.1sec). 
   minimum period = 0.1sec.*/

#code 0xC000
#data 0xD000

#include <startup.c>
#include <68hc11.h> /* to use special register of 68HC11 */
#include <stdio.h>

/* These are included to use fputs */
#include <fopen.c>
#include <fputs.c>
#include <fputc.c>
#include <EVB_out.c>

#define REG_BASE 0x1000

FILE stdout; /* to use fputs */

int done; /* flag: 0-not done,1-pulse measured*/
int first; /* s/w mode flag: 0 -> waiting, 1 -> first edge*/
int factor, count;
 

interrupt tme_ic1() {

     if (first == 0) {
          first = first+1; /* 1st edge detected, not done */
     }
     else {
          done = 1; /* 2nd edge detected, done */
          first = 0;
     }

     bit_set(REG_BASE+TFLG1,0x04); /* clear int. flag */

}

init() {

     done = 0;
     first = 0;
     count = 0;

     pokeb(REG_BASE+TCTL2,0x10); /*EDG1B:EDG1A = 0:1, IC1 rising edges*/
     bit_set(REG_BASE+TFLG1,0x04); /* clear IC1 flag, if any */
     bit_set(REG_BASE+TMSK1,0x04); /* enable IC1 interrupt */
     bit_set(REG_BASE+TFLG2,0x40); /* clear RTI flag, if any */
     bit_set(REG_BASE+TMSK2,0x40); /* enable RTI interrupt */
     bit_set(REG_BASE+PACTL,0x03); /* set rate to 32.77ms */
     e_int();

}

 

/********************************************************

* This service routine gets called every 32.77ms. count is

* incremented each time until = 3 (100ms has passed). "factor"

* is incremented every 100ms since the first edge is detected.

* The period is (factor * 100ms).

*/

 

interrupt rti(){

     if(count == 3){ /* 100ms has passed */

     count = 0; 

     if(done ==1){

          d_int(); /* disable interrupt */

          stdout = fopen(EVB_out);

          printdec(factor * 100); /* print the period out to screen */

          fputs(" ms\n", stdout);

          done = 0; /* reset done flag for next measurement */

          factor = 0; /* reset for next measurement */

          e_int(); /* enable interrupt */

     }

     else if(first == 1) factor = factor + 1;

     else ; 

     }

     else count = count + 1; /*keep track of when 100ms has passed*/

     bit_set(REG_BASE+TFLG2,0x40); /*clear int. flag */

}

 

main(){ 

     poke(0xE9,tme_ic1); /* make tme_ic1 an int. service routine*/

     poke(0xEC,rti); /* make rti() an int. service routine */

     init(); 

     while(1){ ; 

     }

}