Fwd: Re: [avr-chat] Error in Timing.

[Royce Pereira]

Hi,
It seems this mail I sent to the list on the 2nd March has not been posted on 
the list. I'm still recieving replies, although my problem was solved as 
described below - the 3rd time I'm sending this mail, and hope the list gets it 
this time.

Also, The mails(archive) have not been updated since the 1st Mar ??

--Royce
------- Forwarded message -------
From: "Royce Pereira" <address@hidden>
To: AVR-CHAT <address@hidden>
Cc: address@hidden
Subject: Fwd: Re: [avr-chat] Error in Timing.
Date: Thu, 02 Mar 2006 09:38:06 +0530

Hi James,

------- Forwarded message -------
From: "James Washer" <address@hidden>
To: address@hidden
Cc:
Subject: Re: [avr-chat] Error in Timing.
Date: Thu, 02 Mar 2006 00:00:35 +0530

> With a prescale of 8, you may be missing a few counts to TCCNT0 before you reset 
> it... try using >a larger prescaler.

Yes you were right. That was what was happening. The accuracy improved 
dramatically after setting a higher prescaler value.

In fact, even with the internal RC osc, the accuracy was acceptable for my app. 
(2 sec error in 20 mins). So I could do away with the crystal(which I had added 
to solve this problem).

Only inconvenience now is getting divisions to get 1ms,10ms. This was possible 
with the prescaler at CK/8 (4000000/8 = 500000 i.e 0.5 ms, so getting 10ms, 
20ms was easy). Now I have prescaler at CK/256 giving 15625 Hz, a non factor of 
10 :(.

But the main issue is resolved. Thank you,James, & all who responded!

--Royce
-----------------------------------------------------------------------
On Wed, 01 Mar 2006 23:37:49 +0530
"Royce Pereira" <address@hidden> wrote:

> Hi,
>
> On Wed, 01 Mar 2006 21:51:37 +0530, James Washer <address@hidden> wrote:
>
> >
> > Post you timing code.. including initialization and interrupt handler
>
> OK, here it is:
> //========================================
> #define F_CPU   4000000
> ISR(TIMER0_OVF_vect) //interrupt handler for Timer0
>     {
>        TCNT0= ~250; //for 0.5ms
>        //------------------
>        if(!--ms100)   //100 ms counter.
>           {
>              ms100=200;
>                 if(!--sec)
>                 {
>                    sec=10;
>                    if(user_time)
>                         {
>                            if(!--user_time)             
>                               {
>                            //...beep the buzzer, relay on, etc
>                                 }
>                         }
>            }
>         //....etc.
>         return;
>     }
> //=================================
> int main(void)
>         {
>        TCCR0=2;    //prescaler= CK/8
>        TCNT0=~250;  //divide furthur by 250 for 0.5ms interrupts.
>        TIMSK=1;    //Enable Timer0 interrupt.
>        sei();      //enable global interrupts
>
>         while(1)
>         {
>         //.....other stuff(display etc)
>         }
>         return 0                
>         }
> //===================================
>
> Thanks,
> --Royce.
> --
> Using Opera's revolutionary e-mail client: http://www.opera.com/mail/



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