Lpc2000

--- In lpc2000@yahoogroups.com, "brendanmurphy37"
<brendanmurphy37@...> wrote:
>
> --- In lpc2000@yahoogroups.com, "jayasooriah" <jayasooriah@> 
> No need to say the same thing four times: they all miss the point in 
> any case.
> 
> The point isn't that a peripheral is known to lock up (in fact, I'm 
> not aware any of the LPC2xxx peripherals that exhibit this 
> bevahiour), the point is that there is a risk that such a problem 
> may be present and as yet undiscovered. These deveices are just too 
> complex, and the systems in which they operate so numerous as to 
> make a guarentee of the possibility virtually impossible.

I think you seem to miss my point: that if you find a vendor produces
devices that lockup or do not function properly (like the UART in
LPC), the costs of trying to find the bugs and working around (if this
is possible) are more than moving on to a processor with peripherals
that have a good track record.

> Knowing this risk exists, I've learnt from both my own and others 
> experience that the best thing to do when a watchdog expires is to 
> reset everything back to a known state, and then re-configure as 
> required. If this is what the watchdog does, then great.

I advice people to think of costs as an ongoing issue.  Often one
finds that a product appears to be an inexpensive initial investment,
but over the life of the project, this turns out to be more expensive.

> If there's some counter argument (as to why it might be prefereble 
> not to reset back to a known state), I'd love to hear it.

I will restate for you what I have already posted in response to
Robert's questions.

If you want the components of your system external to the CPU to
function without disruption when you take a watchdog timer interrupt,
then you need the processor to preserve its external world interface
as it was, and let you problem and incrementally recover from the
software deadlock in a way that the outside world does not even know
you took this interrupt.

This is relevant if for example you are restarting a device that is
involved talking to a remote system via modem or network.

There are lots of other reasons, and this is why other manufactures do
this.  As I said before, the purpose of the watchdog timer is for the
user to recover from a software deadlock, not a means for the
manufacturer of the device to get you out of a hardware deadlocks. 

> I believe it is always a good strategy to learn from others often 
> hard-one experience.

Critiquing the solution (be it yours or that of another person) is the
key to learning, whether it is by way of examples or experience.

Jaya