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Problem with Timer2 and Timer0 interrupt

 
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mutevaggil



Joined: 29 May 2008
Posts: 8

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Problem with Timer2 and Timer0 interrupt
PostPosted: Sat Jul 26, 2008 4:24 am     Reply with quote
hi everyone. i got a problem.

here is my timer adjustments of timer0:


Code:
 setup_timer_0(RTCC_INTERNAL|RTCC_DIV_8|RTCC_8_bit);
 set_timer0(131);
 enable_interrupts(INT_TIMER0);


My system OSC=40 Mhz so osc. frequency is 10 Mhz and so tosc=0,1microsecond.

interrupt is supposed to work every 100 microsecond. i have counter in timer0 func.

Code:
#INT_timer0
void count_it()
{
counter_val++;
set_timer0(131)
}



and counter_val is shown in screen. but this apprx. 50 second results in just a minute. it must show 60 on screen, but not.

is my compute wrong? i dont think so. so what is my problem?

(i tried it with timer2 too, it also failed.)

PS: i use 18f4431

Last edited by mutevaggil on Tue Jul 29, 2008 4:50 am; edited 1 time in total
Ttelmah
Guest
PostPosted: Sat Jul 26, 2008 9:02 am     Reply with quote
Do some searches here.
The problem is fundamentally, that interrupts take _time_. With a counter advancing every 8 instruction times, the timer will probably already have advanced by several counts, before you get to your instruction setting the count. When you then set the timer, this advance is 'lost', so the timer is then seen to run slow.
Preferably, either use a timer that supports resetting at a count in hardware (timer2), or adjust your code so you don't have to reset the timer value. As a 'worst case' solution, _add_ your required offset to the value read from the timer (this can still give errors if the timer increments between the read and the write).
There have been a huge number of threads here about this, and different methods of avoiding problems.

Best Wishes
mutevaggil



Joined: 29 May 2008
Posts: 8

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its done
PostPosted: Tue Jul 29, 2008 4:48 am     Reply with quote
thanks ttelmah,

i listened your advice and did some searches here. you really answered hundreds of time for the same problem. and of them worked for me.

i just kept PR2 short. i mean:

Instead of TIMER2(DIV_BY_1, 124, 8) //100us,

TIMER2(DIV_BY_4,24, 10) //100 us worked very well.

i am writing this here because this may be help any other people who face to same problem.


thanks.
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