topic Re: Watchdog Timer Reset unexpected behaviour in LPC Microcontrollers

Watchdog Timer Reset unexpected behaviour

lpcware — Wed, 15 Jun 2016 19:20:24 GMT

Content originally posted in LPCWare by hangdog on Wed Oct 01 05:11:53 MST 2014
Hi

I'm trying to use the watchdog timer to reset an LPC4350 - the device stops running, but seems never to start again. When I hard reset using the reset button on the dev board (DIOLAN), it comes back as expected. What I don't get is... isn't using the WDT equivalent to pressing the reset button? Or did I miss something?

The only other information that might be pertinent is that various interrupts are enabled, so other code can potentially run whilst the WDT is counting down, but this is the only place in the code base that I touch the WDT, so I can't see why anything would get in its way.

Cheers for any insight, my WDT reset code follows:

WWDT_TC = 0xFFFF;
WWDT_MOD = BIT0 | BIT1;
WWDT_FEED = 0xAA;
WWDT_FEED = 0x55;
while (1)
{
}

Re: Watchdog Timer Reset unexpected behaviour

lpcware — Wed, 15 Jun 2016 19:20:25 GMT

Content originally posted in LPCWare by hangdog on Thu Oct 30 13:05:28 MST 2014
Bump - on the off chance a super hero is passing by...

Re: Watchdog Timer Reset unexpected behaviour

lpcware — Wed, 15 Jun 2016 19:20:26 GMT

Content originally posted in LPCWare by starblue on Fri Oct 31 04:15:01 MST 2014

Quote: hangdog
isn't using the WDT equivalent to pressing the reset button?

That's not so easy, the startup code might check whether a watchdog reset occurred.

Re: Watchdog Timer Reset unexpected behaviour

lpcware — Wed, 15 Jun 2016 19:20:26 GMT

Content originally posted in LPCWare by hangdog on Fri Oct 31 06:37:09 MST 2014
Hi starblue

Thanks for your comment.

As someone previously suggested to me, I have read Ch14 of the user manual, and as far as I can see the relevant entry is Table 165, which describes a CORE_RST as being generated by either the external reset pin or by a WWDT timeout reset. That is, they're the same, aren't they? Fig 36 seems to indicate the same thing.

What I didn't state in my original post was that the reset does work most of the time, it just fails to come back occasionally. I can't see any pattern to when it does this.

So, what startup code are you referring to, the device ROM? Have you any notion that the behaviour of the ROM might be different following a WWDT reset?

Cheers

Re: Watchdog Timer Reset unexpected behaviour

lpcware — Wed, 15 Jun 2016 19:20:27 GMT

Content originally posted in LPCWare by starblue on Mon Nov 03 05:26:48 MST 2014

Quote: hangdog
So, what startup code are you referring to

No, just a generic assumption that the startup code in your software might do something different (e.g. count the number of watchdog resets to prevent a loop).

Quote: hangdog
the device ROM? Have you any notion that the behaviour of the ROM might be different following a WWDT reset?

It seems they removed an erroneous mention in the boot flowchart that was in some earlier version of the UM, maybe I had that in the back of my mind.

So I guess you have to work on developing your own super powers ...