Can not debug with ICD-3 while using wdt

[amit78]

Hello All,

I am using ICD 3, with MPLAB IDE. I know the limitation.

[PCM programmer]

You could possibly emulate the Watchdog with a Timer interrupt.
Just have a global variable and decrement it inside the Timer isr.
Let's say the Timer interrupt occurs every 1 ms. Then initialize
your global counter to 128 (let's say) for a 128 ms emulated WDT
timeout period.

Inside the Timer isr, when or if the global counter variable gets
decremented down to 0, then call the cpu_reset() function.
This will be your emulated WDT reset.

In the rest of your program, everywhere that you have a restart_wdt()
statement, you should add a statement to reload the global counter
with the initial value (128, for example).

It's possible that a fault in your program could stop the Timer interrupts.
In that case, the Watchdog reset emulation would fail. You could check
this by toggling an LED at a 2 Hz rate inside the isr. As long at the LED
is blinking, then you know you have Timer interrupts working, and your
WDT emulation is also probably still working.

You could surround all the WDT emulation lines with

[temtronic]

hmm..
"I have written a huge and complicated code with PIC18F452"

Hopefully you started with small sections of code, debugged them,got them 100% working before you combined into a 'huge and complicated' program!
If not, you're in for a LOT of head scratching, trying to figure out why 'something' doesn't work correctly.
Enabling the WDT is probably the last step in any major program,after having verified all the other code works, as the WDT is a type of 'failsafe' feature.

Also, be aware that the WDT timing is NOT precise.Check the datasheet for the specs.



hth
jay

[amit78]

Thank you all.

To PCM programmer

Got a simple and nice idea. It will definitely work.


To temtronic

Yea that is true. The code has small small modules. Each module has its own unit testing. so we do debug them without wdt. But now while we integrated the code, we need to test it with wdt. There are some requirement of restart the micro. But some are working some are not, thats why we need to debug.

Thank you all. I will suggest my team for software wdt.

Amit

[Ttelmah]

and for 'testing', you need to remember just how inaccurate the WDT is on most chips. We are not talking a +/-10% type error, but 400%+. Typically the '21mSec' watchdog, can trigger anywhere from perhaps 7mSec to 30mSec, on different chip examples. Nothing worse than debugging everything, then finding that there is one part of the code that does not refresh the watchdog, which leave 8mSec, so on just one chip in a thousand, the watchdog triggers....

If you have a spare pin, and the MCLR is enabled, you can implement a 'hardware' watchdog simulator breakout. Replace 'restart_wdt', with code to toggle the spare pin. Have a little timer (perhaps a PIC12F675 or similar), which if it doesn't see this toggle, pulses MCLR low. If you want to use 'restart_cause', so that you can implement watchdog recovery, then a second pin is needed, and have the little timer set a pin high/low according to whether it has triggered, so you can detect the simulated watchdog.

Best Wishes

[amit78]

My boss suggested me to use chip like MAX691 external watchdog timer .. I am checking it.