Lpc2000

--- In lpc2000@yahoogroups.com, "Ake Hedman, eurosource" <akhe@b...>
wrote:
>

> >
> >
> The absolute majority of watchdogs, internal or external, function by 
> toggling a bit  from time to time. Where in the code  you do this 
> toggling is something you have to investigate for each project. The 
> common point in any case is that if the program pass a certain point in 
> the flow we allow the application to live for n milliseconds more. 

True enough.  :-)

> 
> The 0xAA, 0x55 sequence is nothing else either. It may look safer then 
> toggling a bit but false watchdog triggers have never been a problem
for 
> an extended time during my years as an embedded developer. The chance 
> that your crashed program start to toggle a watchdog bit or write a 
> 0xAA, 0x55 sequence is just minimal and in that light I think Tom's 
> reasoning is fully correct and would not make the watchdogs 
> functionality less good. At least IMHO.

Minimal is NOT zero, so conservative hardware design pratices dictate
erring on the side of caution.  IMHO, that reasoning makes the
software design task easier, but makes the watchdog less reliable when
atomic kick sequences are not required.


> 
> But requiring the 0xAA,0x55 sequence is acceptable to of course. The 
> need to mask interrupts while doing it is not. Thats really bad.
> 
Bad is probably a matter of opinion?
More difficult, certainly.

The need for atomic code sequences is not all that unusual, so it is
just something that needs to be dealt with in the software design,IMHO.


-- Dave