Lpc2000

Hello,
One question about WDT feeding.

The user manual is (once more) not exatcly clear about WDT refresh.
It says that after writing 0xAA to WDTFEED, 'the next operation in 
watchdog register space should be a write 0x55 to WDTFEED', otherwise 
the watchdog will reset the cpu even if the timer is not yet elapsed.

What happens if one interrupt triggers between 0xAA and 0x55?

I see the wdt resets cpu, even if the ISR does not affect WDT 
register space.

Do I need to disable interrupts before feeding WDT?

Thank you.

As far as I know, yes. Feed sequence must not be interrupted. 

Kerem

----- Original Message ----- 

From: "extra300_it" <roberto.labaa@...>
To: <lpc2000@yahoogroups.com>
Sent: Thursday, February 03, 2005 4:49 PM
Subject: [lpc2000] WDT feed


> 
> 
> Hello,
> One question about WDT feeding.
> 
> The user manual is (once more) not exatcly clear about WDT refresh.
> It says that after writing 0xAA to WDTFEED, 'the next operation in 
> watchdog register space should be a write 0x55 to WDTFEED', otherwise 
> the watchdog will reset the cpu even if the timer is not yet elapsed.
> 
> What happens if one interrupt triggers between 0xAA and 0x55?
> 
> I see the wdt resets cpu, even if the ISR does not affect WDT 
> register space.
> 
> Do I need to disable interrupts before feeding WDT?
> 
> Thank you.
> 
> 
> 
> 
> 
> 
> 
> 
> Yahoo! Groups Links
> 
> 
> 
> 
> 
> 
> 
>

At 02:49 PM 2/3/05 +0000, extra300_it wrote:
>The user manual is (once more) not exatcly clear about WDT refresh.
>It says that after writing 0xAA to WDTFEED, 'the next operation in
>watchdog register space should be a write 0x55 to WDTFEED', otherwise
>the watchdog will reset the cpu even if the timer is not yet elapsed.
>
>What happens if one interrupt triggers between 0xAA and 0x55?

The WD feed fails.

>I see the wdt resets cpu, even if the ISR does not affect WDT
>register space.

That's to be expected.

>Do I need to disable interrupts before feeding WDT?


Yes.

Robert

" 'Freedom' has no meaning of itself.  There are always restrictions,
be they legal, genetic, or physical.  If you don't believe me, try to
chew a radio signal. "

                         Kelvin Throop, III

Yes, disable ALL interrupts when writing the AA and 55 then re-enable them.

  -----Original Message-----
  From: extra300_it [mailto:roberto.labaa@...]
  Sent: Thursday, February 03, 2005 9:50 AM
  To: lpc2000@yahoogroups.com
  Subject: [lpc2000] WDT feed



  Hello,
  One question about WDT feeding.

  The user manual is (once more) not exatcly clear about WDT refresh.
  It says that after writing 0xAA to WDTFEED, 'the next operation in
  watchdog register space should be a write 0x55 to WDTFEED', otherwise
  the watchdog will reset the cpu even if the timer is not yet elapsed.

  What happens if one interrupt triggers between 0xAA and 0x55?

  I see the wdt resets cpu, even if the ISR does not affect WDT
  register space.

  Do I need to disable interrupts before feeding WDT?

  Thank you.







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[Non-text portions of this message have been removed]

When I first started with the LPC210x and Watchdog my board would 
sporadically crash - mainly then when I was dumping data to the 
serial port (lots of SCI interrupts).

I decided to protect the feed sequence from interrupts and this 
cured the problem - since then the system is as solid as a rock.

Therefore the feed sequence should absolutely be protected against 
interrupts!!!

regards

Mark Butcher

www.mjbc.ch



--- In lpc2000@yahoogroups.com, "extra300_it" <roberto.labaa@l...> 
wrote:
> 
> Hello,
> One question about WDT feeding.
> 
> The user manual is (once more) not exatcly clear about WDT refresh.
> It says that after writing 0xAA to WDTFEED, 'the next operation in 
> watchdog register space should be a write 0x55 to WDTFEED', 
otherwise 
> the watchdog will reset the cpu even if the timer is not yet 
elapsed.

> 
> What happens if one interrupt triggers between 0xAA and 0x55?
> 
> I see the wdt resets cpu, even if the ISR does not affect WDT 
> register space.
> 
> Do I need to disable interrupts before feeding WDT?
> 
> Thank you.