delay in main causes delay in timer0 interrupt

[mutthunaveen]

Dear Forum

yesterday i started to write a program in 16F676 uC.

i used internal OSC 4Mhz
1. Timer0
2. EXT INT
3. Void main with Infinity loop.

1. timer 0 (toggle YELLO LED when a variable de-pleats inside timer0)
2. EXT INT (inside toggle a GREEN LED with a small delay (delay_ms(10)))
3. Void main Infinity loop (toggle RED LED with (delay_ms(1000))

problem -->
when delay in main is removed the Timer0 works fine
when delay in main is enabled then timer0 delay is also correspondingly increasing.

where is wrong? can someone help me.

thank you

[Ttelmah]

You will be getting a warning saying that interrupts are disabled to prevent re-entrancy.

Problem is that you are using the delay routine, both inside an interrupt (INT_EXT), and outside. A function cannot be called from inside itself in the PIC (this is 're-entrancy'). So to prevent the possibility of the delay function being called from inside the delay function, interrupts have to be disabled when you use the delay in the main.....

Now, realistically using a delay inside an interrupt (except for the very shortest ones using a couple of cycles of delay), is 'not good practice'. General thing is that interrupt handlers should always exit 'ASAP'. If you want something to happen a moment after doing something in an interrupt, then program a timer to trigger at the interval required, and use an interrupt from this. As a separate thing, consider not using 'delays' in the main code at all. If (for instance) you have an interrupt triggering every few hundredths of a second, use this to time your delays. Have a simple counter. In the interrupt have something like:

[mutthunaveen]

Dear Ttelmah

Thank you for the elaborated explanation. Now i got the complete knowledge on how delay impact interrupt and how to smartly apply delays.
Best practice is not to use Delay anywhere in code unless it is too short.

Thank you Ttelmah