Lpc2000

Hi Guille,

I have seen this problem before on 2292 and the culprit appears to be what 
the boot loader does on watchdog resets when there is on-chip flash with 
external memory boot capability.

The "USAGE NOTES ON WATCHDOG RESET AND EXTERNAL START" section of 2292 
explains (in a longish way) the limitations (see below).

If you cannot guarantee that certain GPIO signals (not just those 
documented) are not in a particular state when configured as input at the 
time watch dog timer fires, you can lock yourself up in ways and require 
hard reset.

It does not matter if you are not using the external boot feature, or for 
that matter, use the external memory interface.

It is a pity, this appears not to be a processor limitation, but a boot 
loader limitation or bug.  I have not had time to look at the boot loader 
source as yet.

Jaya

>USAGE NOTES ON WATCHDOG RESET AND EXTERNAL START
>
>When LPC2292/2294 is conditioned by components attached to the BOOT1:0 
>pins to start execution in off-chip memory, and is programmed to enable 
>the Watchdog Timer to reset the part if it is not periodically serviced, 
>care must be taken to avoid problems due to the interaction of these features.
>
>First, the BOOT1 and/or BOOT0 pin(s) must be biased to ground using 
>pulldown resistors, not transistors driven from RESET low, because RESET 
>is not driven low during a Watchdog Reset.
>
>Second, if either or both of the BOOT1:0 pins are used as inputs in the 
>application, the application designer must ensure that the external driver 
>will not be enabled during an internal Reset generated by the Watchdog Timer.
>
>(One way to do this is to use one of the CS3:0 outputs to enable the driver.)
>
>If these two conditions cannot be met, an external Watchdog facility can 
>be used.


>    Date: Mon, 06 Feb 2006 12:53:07 -0000
>    From: "Guillermo Prandi" <yahoo.messenger@...>
>Subject: Bootloader not always invoked after reset with P0.14 low
>
>...
>
>5) At T+840 mS, P0.14 goes up sharply. This is 338 mS *after* reset
>went high.
>
>By the spec, these figures should be large enough to trigger the
>bootloader, and it does, except when I've been playing around with my
>firmware for a while (several cycles of compile+flash programming,
>tests, an occasional crash, watchdog triggered, etc.). When the
>bootloader stops responding, the only way to regain the bootloader is
>by removing power.
>Any ideas?
>
>Guille

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