On Wednesday 23 September 2009, freddie_cho...@op.pl wrote:
> "Petri Pirttinen" <petri.pirtti...@tietolaite.com> napisał(a):
> > I may have missed something in here, but why trying to specify a crystal
> > frequency? Can't we use 4 MHz in here, IF we are setting the clock
> > source to internal RC oscillator in reset-init script anyway?
>
> 1. Not all LPCs have internal RC - just the "more recent ones"
> from LPC23xx and LPC24xx family - older ones (LPC21xx and LPC22xx)
> need a crystal to start and run.
And that hardware is not restricted to 12 MHz crystals...
> 2. To clarify - 12MHz is the default value for the chips without
> the RC. The ones that do have it have that frequency configured to 4MHz.
I don't see how that can be right either, except on chips that
have a real way to halt-on-reset ... and as I understand, these
chips from NXP don't support that. So chip startup code will run,
and likely set up some clocking stuff first thing, which will be
neither 4 MHz nor 12 MHz but something appropriate to the board
and the application int manages.
> > And, Freddie, I hope you can bear with this conversation. I think that
> > these things discussed in here does relate to each other, although some
> > of them needs to be addressed separately really. In all and all I'm
> > quite thrilled about this as finally I get some light shred to this
> > LPC2xxx mess. Your proposed script layout is A LOT better than any I've
> > seen so far.
>
> The things are related - true, but there is no problem in finishing with
> one and starting another then, not to simultaneously think about 10
> different things. IMHO we'll never go anywhere while "jumping around"
> like this.
Agreed. But there's no "jumping around" here; just the normal sort
of requirement that each incremental step be correct.
> Anyway - to be honest - I don't know what should I / we do now. The
> frequency IS required, it has to be specified some way or another.
> Unfortunatelly I think only the method proposed in the file I posted
> is user friendly - the need for next "wrapper script" that would specify
> that just because "frequency is not specific to targets" seem extremely
> "un-friendly" to me.
A "wrapper" is already required to associate the right JTAG adapter
with the right target. I fail to see how adding the "set" in this:
source [interface/...cfg]
set CRYSTAL_SPEED 3579545
source [target/...cfg]
is "unfriendly" ... especially compared to setting the wrong value
for the clock speed, so flash write timings are broken.
- Dave
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