Hi guys,
I have problems with the folowing piece of code. I modified the
original example from Microchip C18 which implements TIMER0 interrupt
and i added PORTB on-change interrupt. The code does only one thing :
it increments pulse_count.b1234 which is an unsigned long (this being
made inside ISR) when it detects a change from 0 to 1 on RB4 and in the
main loop sends the value to PORTC so i can see it.
I tested this code using Proteus VSM and it works well. I applied an
impulse train on RB4 and the programs acts as it shoul with only one
problem : after ~30 seconds it behaves erratically for a few moments and
starts to count again from 0 !
I disabled watchdog timer (even from VSM), i disabled LVP, i disabled
BOR, i disabled Stack overflow reset, no luck whatsoever.
Can anyone see if i am doing something wrong with the folowing piece
of code ? I have the .lst as well as .hex files if that might help. I
have been doing this for the last 10 hours and i feel like i am
loosing my mind.

Thank you for your understanding,

//----------------------------------------------------------------------------


#include <p18F252.h>
#pragma config OSC = XT, OSCS = OFF, PWRT = ON, BOR = OFF, WDT = OFF,
STVR = OFF, LVP = OFF, DEBUG = OFF

//----------------------------------------------------------------------------

void main (void);
void InterruptHandlerHigh (void);

union {
  struct  {
    unsigned Timeout:1;         //flag to indicate a TMR0 timeout
    unsigned None:7;
  } Bit;
  unsigned char Byte;
} Flags;

//=========================
union {
        struct {
                unsigned char B0;
                unsigned char B1;
                unsigned char B2;
                unsigned char B3;
                } byte;
                unsigned long b1234;
} pulse_count;


//=========================
union {
  struct {
    unsigned RB0:1;
    unsigned RB1:1;
    unsigned RB2:1;
    unsigned RB3:1;
    unsigned RB4:1;
    unsigned RB5:1;
    unsigned RB6:1;
    unsigned RB7:1;
        };
        unsigned char old_portb;
} old_portb_bits;

//----------------------------------------------------------------------------
// Main routine

void main () {
        Flags.Byte = 0;
        INTCON = 0x28; //disable global and enable TMR0 interrupt and RB
        INTCON2 = 0x85; //TMR0 high priority
        RCONbits.IPEN = 1; //enable priority levels
        TMR0H = 0; //clear timer and set TMR0H
        TMR0L = 0; //clear timer low byte and also updates high byte from TMR0H
        T0CON = 0x88; //set up timer0 - no prescaler
        INTCONbits.GIEH = 1; //enable interrupts
        TRISB = 0x7E; //PORTB bits 0 and 7 are output, the rest are input
        TRISC = 0; //PORTC bits are output
        PORTC = 0;

        old_portb_bits.old_portb = 0;
        pulse_count.b1234 = 0;
        
        while (1) {
                PORTC = pulse_count.byte.B0;
        }
}

//----------------------------------------------------------------------------
// High priority interrupt vector

#pragma code InterruptVectorHigh = 0x08
void
InterruptVectorHigh (void)
{
  _asm
    goto InterruptHandlerHigh //jump to interrupt routine
  _endasm
}

//----------------------------------------------------------------------------
// High priority interrupt routine

#pragma code
#pragma interrupt InterruptHandlerHigh

void InterruptHandlerHigh () {

        if (INTCONbits.TMR0IF) {                                //check for TMR0 overflow
                INTCONbits.TMR0IF = 0;                          //clear interrupt flag
        }

        if (INTCONbits.RBIF) {
                PORTB = PORTB;
                INTCONbits.RBIF = 0;
                if (PORTBbits.RB4 == 1 && old_portb_bits.RB4 == 0) (unsigned long)pulse_count.b1234++;
                old_portb_bits.old_portb = PORTB;
        }
}

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