PSoC timer interrupt

Question

It seems to me that my timer interrupt does not work correctly. Problem is that counter inside interrupt function increments only once. Here is my code from main and timer settings.

#include <m8c.h>
#include "PSoCAPI.h"
#include <stdio.h>
#include <stdlib.h>

char theStr[] = "PSoC LCD";
static char tmp[3];
static int counter = 0;

void main(void){

    LCD_Start();
    LCD_Position(0,5);
    LCD_PrString(theStr);
    M8C_EnableGInt;
    Timer8_EnableInt();
    Timer8_Start();
    while (1);
}

#pragma interrupt_handler myTimerInt
void myTimerInt(void){
    counter ++;
    LCD_Position(1,0);
    itoa(tmp, counter, 10);
    LCD_PrString(tmp);
}

The thing about interrupt handlers is that they should be small, fast and especially not cause nested interrupts to occur. — Some programmer dude, Mar 30 '14 at 11:02
@JoachimPileborg - yeah, 'LCD_Position' does not sound like something I would call from an interrupt-handler. — Martin James, Mar 30 '14 at 11:32
Indeed, printing to the LCD could be a bit time consuming. How often does the timer interrupt fire? Does the code start working if the rate of timer interrupts is drastically reduced? — Chris Stratton, Apr 02 '14 at 02:36

score 1 · Accepted Answer · answered Apr 02 '14 at 00:29

1

Most interrupt service routines need to re-arm the interrupt (sometimes called "acknowledging the interrupt) which called it. Otherwise, the ISR is only called once. Typically, this is done after the critical part of the ISR is complete.

In the case of the 503418, I think the reenabling is done by reading the counter register. See the code at the bottom of this.

answered Apr 02 '14 at 00:29

wallyk

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That's right, interrupt was called only once. Made it easier using only flag and it works now. Thank you. – mikedanylov Apr 25 '14 at 19:54

score 0 · Answer 2 · 2014-04-03T13:40:28.630

A possible problem you might have is a misconfigured interrupt service routine in Timer8INT.asm. When using the directive #pragma interrupt_handler you need to make sure you're using the right instruction to call the C interrupt service routine in your Timer8INT.asm ISR.

If this directive is defined a reti instruction will be add to the end of that function which is incorrect if you use lcall to call that C function from your Timer8INT.asm. In this case you actually need a simple ljmp instruction to that C function.

When using directive #pragma interrupt_handler Timer8INT.asm should have

_Timer8_ISR:

    ljmp _myTimerInt

    reti

Without directive #pragma interrupt_handler Timer8INT.asm should have

_Timer8_ISR:

    PRESERVE_CPU_CONTEXT
    lcall _myTimerInt
    RESTORE_CPU_CONTEXT

    reti

PSoC timer interrupt

2 Answers2