[Tinyos-host-mote-wg] Re: [Tinyos-2.0wg] mica2 timer / problems @ 32kHz

[Joe Polastre]

Yeah, the problem was the external crystal.  I would ditch that thing
if I were you, as all of the B-MAC code that both Jason and I wrote
assumes that you're using the internal oscillator instead of the
external crystal.

-Joe

On 8/20/05, Robert Szewczyk <szewczyk at eecs.berkeley.edu> wrote:
> Looking at the timer in 1.x it appears that it sets the maximum tick interval to 230.
> 
> I could not make it work reliably with anything over 250.  There was something weird going on with wakeup from power save mode when running w. external xtal (4ms warmup time).  I don't know if that also happened with the internal RC oscillator (60us wakeup or so); it might make sense to try it with the short wakeup.   The old timer that did use (or handle) overflow at all, I believe the new Alarm/Timer mechanism does use compare and overflow timers correctly; with these I would expect the timer system to work.
> 
> Rob
> 
> ----- Original Message -----
> From: David Gay <dgay42 at gmail.com>
> Date: Friday, August 19, 2005 8:42 pm
> Subject: Re: [Tinyos-2.0wg] mica2 timer / problems @ 32kHz
> 
> > On 8/19/05, Phil Levis <pal at cs.berkeley.edu> wrote:
> > > On Fri, 2005-08-19 at 17:22, David Gay wrote:
> > > > While testing the prerelease, I found that the radio no longer
> > > > appeared to work with any reliability... Further investigation
> > > > suggested the problem was with timers, and much further
> > investigation> > suggests that the atmega128 loses timer0 overflow
> > interrupts when the
> > > > timer0 compare register is 254 or 255 (at least when it's
> > running w/o
> > > > a divider).
> > > >
> > > > Question 1: has anyone else seen effects like this with the
> > atmega128> > timer0? Or is some other mysterious bug causing the
> > problem? (note
> > > > that just avoiding 254 or 255 doesn't seem to quite make
> > problems go
> > > > away, though I could at least get a regular 1Hz blink when the
> > radio> > was enabled...)
> > > >
> > > > Question 2: the problem can be (apparently, at least)
> > alleviated by
> > > > using a 4kHz basic clock rate (i.e., divide by 8). Is this a
> > practical> > solution? (i.e., will it work for micaz?)
> > > >
> > > > Question 3: the easiest fix for the prerelease would seem to be to
> > > > remove the 32kHz timer, and just run timer0 at 1kHz. Comments?
> > > >
> > > > I'll try and create a more isolated test case Monday.
> > >
> > >
> > > I know that when Rob first wrote the timer (for GDI), he had 240
> > as the
> > > maximum overflow value...
> >
> > Rings a bell. And I think the 1.x timer currently stops at around 200?
> > Rob, any comments?
> >
> > David
> >
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