[Tinyos-host-mote-wg] RE: [Tinyos-2.0wg] TinyOS Telecon Notes 8/31/05

[mturon at xbow.com]

The external oscillator is available for users who are concerned with UART
reliability -- with it they can achieve 100%.  With 8MHz, maximum
reliability of the ATmega128 UART is 99.8%.  Therefore, use of the internal
osc is not practical for *everything*, but it is mandatory for low power.

I think it is important that we think this through for Timers -- we need a
way to specify at init time the source clock of the chips/MCU, because we
cannot assume it is always the same.  The BusyWait component should adjust
accordingly -- most black magic is related to TOSH_uwait not working when
clock source assumption is wrong.  Such an interface would make mica2dot
support much easier, as the 4MHz CPU clock is the primary difference there.

Martin 
__________________________________________________
Martin Turon  |  Crossbow Technology, Inc.

-----Original Message-----
From: Joe Polastre [mailto:joe.polastre at gmail.com] 
Sent: Friday, September 02, 2005 3:07 AM
To: mturon at xbow.com
Cc: bengreenstein at gmail.com; tinyos at barnowl.org
Subject: Re: [Tinyos-2.0wg] TinyOS Telecon Notes 8/31/05

Thanks Martin, but you didn't answer my question... Do you plan to use
the internal oscillator for *everything*, or are you still planning on
using the external oscillator?  If so, why?  Using the internal makes
life easier for everyone.  Besides, if you calibrated the oscillator,
then Jason Hill's black magic would work across platforms ;)

-Joe

On 9/1/05, mturon at xbow.com <mturon at xbow.com> wrote:
> Hi Joe,
> 
> The internal oscillator is default for low-power apps.  This opens up a
> discussion on initialization of timers.
> 
> We need to think about timer initialization and how to allow multiple
> configurations.  Some users will want to set an MCU to a different clock
> speed.  What API do we use to specify this?
> 
> Martin
> __________________________________________________
> Martin Turon  |  Crossbow Technology, Inc.
> 
> -----Original Message-----
> From: Joe Polastre [mailto:joe.polastre at gmail.com]
> Sent: Thursday, September 01, 2005 4:29 AM
> To: Ben Greenstein
> Cc: mturon at xbow.com; tinyos at barnowl.org
> Subject: Re: [Tinyos-2.0wg] TinyOS Telecon Notes 8/31/05
> 
> > Phil: I agree. It should take something like 60-80 cycles to compute
> > the power state of the mcu. Let's consider the notion of a dirty
> > bit. If anything changes in the power state, the dirty bit isset. The
> > MCU goes into same state as the last time unless this bit is set. When
> > set it recomputes. ... Is this notion something that would be usesful
> > for eyes?
> 
> Note about Phil's comment:
> 
> This won't work if you're using a DMA or other such device that relies
> on other hardware components.  It makes setting the "dirty" bit very
> difficult.
> 
> Besides, 60-80 cycles is at most 20us of computation.  Considering it
> takes longer than that for the Atmel to wake up, I don't see a problem
> doing the computation.
> 
> Martin-- What is going to be the "default" oscillator for mica2 and
> micaz?  Seems like using the external oscillator is like shooting
> yourself in the foot before you even start.  Does Xbow have any plans
> to calibrate the internal Atmel oscillator?  Is there even a reason to
> include the external oscillator on the board?  Obviously we don't use
> one on Telos/Tmote or Eyes, and there's at least one "micaz clone"
> that don't have it either.
> 
> -Joe
>

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