Watchdog fuse bit

Pzx · Joined: 05 May 2015 Posts: 39

Hello, I would like to use Watchdog always on fusebit to be more safe and independent from unexpected software crash, but it seems not work properly.
My test program is very simple:

Config Watchdog = 1024
Start Watchdog

Do
Reset Watchdog
Toggle LED
Waitms 1
Loop
End

With Watchdog controlled by software fuse bit selected everything is ok, but when I select Watchdog always on fuse bit the program doesnt work. Why? What is missing in the code then?

(BASCOM-AVR version : 2.0.7.8 )

Evert :-) · Joined: 18 Feb 2005 Posts: 2156

What processor are you using?

Pzx · Joined: 05 May 2015 Posts: 39

ATMEGA 2560

i.dobson · Posted: Thu Aug 18, 2016 7:32 am Post subject:

Hi,

Could it be that the avr is taking too long to initialise and going into watchdog reset?

Maybe try using the $INITMICRO macro to reset the watchdog during init. Something like:

Pzx · Joined: 05 May 2015 Posts: 39

Hi Ian, you are right Atmega seems to be in permanent reset state,
unfortunately your code doesnt help much.
Any other ideas?

EDC · Joined: 26 Mar 2014 Posts: 971

This micro have even 8s Watchdog(look into datasheet page 66). Try another higher value.
Wait 1 + Toggle can be more than 1024 WD timer
You can also try Waitms 500->Reset WD ->Waitms 500 -> Reset WD + Toggle LED ..and so on if value 1024 is the best for you.

EDIT. Look attached picture.
I often open DAT files and search for interested me values by typing CTRL + F
Here I type WD and voila Wink

i.dobson · Posted: Thu Aug 18, 2016 9:30 am Post subject:

Hi,

Looking through the data sheet, I couldn't find anything on what value will be used for the watchdog reset timer on power up (before the user code starts).

Regards
Ian Dobson

Evert :-) · Joined: 18 Feb 2005 Posts: 2156

If you are using the watchdog with the WDTON fuse you can not change the watchdog registers anymore easy. (Has to be done with in 4 clock cycles)
This is done to prevent that the software accidentally alter the registers.
It's not clear how Bascom handles this and if Bascom takes the setting of the fuse bit in consideration.

Are you using a bootloader?

O-Family · Joined: 23 May 2010 Posts: 320 Location: Japan

This is $initmicro instruction after the execution, would initialize the Watchdog to a minimum of 16ms, I think that it is a bug in the BASCOM.
Only get fixed in the mark, there is not means.

MWS · Joined: 22 Aug 2009 Posts: 2262

Pzx · Joined: 05 May 2015 Posts: 39

Hello, thanks for all your replays Smile

Same more claryfication regarding my hardware:
no Bootloader
external 16MHz cristal oscilator

Also I find interesting info in the Atmel ATMEGA2560 pdf in the Watchdog Timer section:
(There is also timming issue about 4 clock cycles like Evert wrote before)

The Watchdog always on (WDTON) fuse, if programmed, will force the Watchdog Timer to System Reset mode.
With the fuse programmed the System Reset mode bit (WDE) and Interrupt mode bit (WDIE) are locked to 1 and 0
respectively. To further ensure program security, alterations to the Watchdog set-up must follow timed sequences.
The sequence for clearing WDE and changing time-out configuration is as follows:
1. In the same operation, write a logic one to the Watchdog change enable bit (WDCE) and WDE. A logic one
must be written to WDE regardless of the previous value of the WDE bit.
2. Within the next four clock cycles, write the WDE and Watchdog prescaler bits (WDP) as desired, but with
the WDCE bit cleared. This must be done in one operation.

There is also some asm code example:

WDT_off:
; Turn off global interrupt
cli
; Reset Watchdog Timer
wdr
; Clear WDRF in MCUSR
in r16, MCUSR
andi r16, (0xff & (0<<WDRF))
out MCUSR, r16
; Write logical one to WDCE and WDE
; Keep old prescaler setting to prevent unintentional time-out
ldi r16, WDTCSR
ori r16, (1<<WDCE) | (1<<WDE)
sts WDTCSR, r16
; Turn off WDT
ldi r16, (0<<WDE)
sts WDTCSR, r16
; Turn on global interrupt
sei
ret

Im not sure what to do with this code. Is it watchdog configure code only or is it reset Watchdog procedure that I should run periodicly? Can I then use normal Reset Watchdog Bascom function? Unfortunately I am not familiar with asm (thats why I am using Bascom Smile

) so how to implemant this asm code into my Bascom test code?.

MWS · Joined: 22 Aug 2009 Posts: 2262

O-Family · Joined: 23 May 2010 Posts: 320 Location: Japan

If your operation clock is 16MHz, that normally work by my Arduino MEGA250 board.
When Wait was put at the beginning of the program, I didn't normally move, so the whole clearance time of SRAM was doubted.

$Initmicro after the instruction, because the Watchdog is initialized to the minimum of 16ms, it makes no sense to write the ASM code.

MWS · Joined: 22 Aug 2009 Posts: 2262

EDC · Joined: 26 Mar 2014 Posts: 971

I test this with m2560 with WD FuseBit on.

EDIT: I found funny issue. BOOTRST FuseBit must be disabled while programming. I don`t have time to investigation this Very Happy

This code work perfectly Wink