Lpc2000

At 07:19 AM 4/30/06 +0000, jayasooriah wrote:
>--- In lpc2000@yahoogroups.com, Robert Adsett <subscriptions@...> wrote:
> > So the difference would be
> >          - Leaves a different signature behind
> >          - Leaves the I/O in the state it was, quite possibly
>increasing
> > the latency to a known good state.
> >
> > The LPC does the first as well,  The second it does differently.
>Better as
> > far as I'm concerned.  However both are reasonably easily dealt
>with.  Only
> > when running close to the edge would that be a deciding factor in
>choosing
> > one over the other.
>
>The approach you refer to as "better" is IMO flawed for the following
>reason:
>
>In the hardware approach, external bus sizing only takes place on
>power on reset.  External bus is invariant for any given system and
>thus a watchdog (or even external reset) does not change this.

Um, Jaya I wasn't referring to external bussed units here.  The issue of 
bus sizing is a separate issue from the rest of the watchdog issues.

>In the LPC approach, the watchdog reset does not preserve bus size
>setting because it does a system reset as a blind reset.
>
>So when a watchdog fires, external bus sizing has to be done all over
>again by software ... but the pins now have taken on a different role
>because these are used as GPIO!
>
>There is no way out.  Watchdog reset and "GPIO" usage of BOOT0 and
>BOOT1 pins are mutually exclusive.  The external device driving this
>input has no way of knowing when the watchdog fires.
>
>In fact, if you think about this carefully, if you are using watchdog
>timer, then you cannot use these pins for output either because these
>have to be strapped so that it does the right thing every time the
>watchdog fires.

Here, I agree with you.  Those are essentially dedicated inputs.  To me it 
looks like marketing overcame engineering sense.  Being able to claim an 
extra two inputs on a check sheet.  Mind you any unit that can afford an 
external bus should be able to afford  a '245 or similar to provide extra 
digital I/O if needed.  If I recall correctly ST did dedicate their 
equivalent lines in that fashion but like I said I don't follow the larger 
units that closely.


>In an earlier post I mistakenly said these were analog inputs.  You
>are right that these are digital inputs.
>
>Analog or digital input or output, the fact remains that these pins
>cannot be used if one uses the watchdog.  I bet Philips throught it
>would be a good idea to sell these bus size strapping pins as GPIO!

Yep,  At the very least it deserves some bold print in the user manual and 
maybe even a footnote in the datasheet as well.

BTW this would be worth adding to the tips,trick, traps section of the 
armuc wiki.

Robert

" 'Freedom' has no meaning of itself.  There are always restrictions,   be 
they legal, genetic, or physical.  If you don't believe me, try to chew a 
radio signal. "  -- Kelvin Throop, III
http://www.aeolusdevelopment.com/