Ultrasonic Ruler

#include <main.h>
#include <flex_lcd.c>

// Ad hoc programming, only for testing purpose (demo).
// Needs to be revised before using.

#define trigger PIN_A1
#define echo PIN_A0
#define button PIN_B0

int32 overflow;

#INT_TIMER1
void tm1_int(){
   overflow++;
}

long tr_strobe(){
   set_timer1(0);
   while( input(echo) );
   output_high(trigger);
   delay_ms(1);
   output_low(trigger);
   while( ! input(echo) );
   setup_timer_1( T1_INTERNAL |  T1_DIV_BY_8 );
   while( input(echo) );
   setup_timer_1( T1_DISABLED |  T1_DIV_BY_8 );
   return(get_timer1());
}

void main()
{
   lcd_init();
   port_b_pullups(true);
   printf(lcd_putc, "Hello World!\nPress Button.");
   while( input(button) );
   lcd_init();

   int32 ctime;
   int distance_m;
   int32 distance_cm;
   int32 time_ms;
   int time_s;

   enable_interrupts(GLOBAL);
   enable_interrupts(INT_TIMER1);
   printf(lcd_putc, "Time:\nDist.:");


   while(true){
      set_timer1(0);
      overflow=0;
      ctime=tr_strobe();
      ctime = (ctime | (overflow<<16));
      ctime = (ctime << 3);
      ctime = ctime / 10;
      time_s = ctime / 100000;
      time_ms = ctime - time_s * 100000;
      lcd_gotoxy(6,1);
      printf(lcd_putc, "%3.1u.%05lu s", time_s, time_ms);
      lcd_gotoxy(7,0);
      if(time_s==0 && time_ms < 40000){
         distance_m = 17 * ( ( ctime + 5 ) / 10 ) / 1000;
         distance_cm = ( ( 17 * ctime + 5 ) / 10 - 1000 * distance_m + 5 ) / 10;
         printf(lcd_putc, "%5.1u.%02lu m", distance_m, distance_cm);
      }
      else {
         lcd_putc("   --.-- m");
      }
      while(input(PIN_B0));

   }

}