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Re: MT4BB Halting
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Watchdog timers are awesome and easy to implement internally in most any micro.? Here is an external one in an old-fashioned dip: As Barry pointed out, you can deadbug it by gluing it upside down with epoxy or such, and soldering to the pins in the air.? However, the watchdog needs a periodic reset within its timeout window, and the firmware needs to provide this on a pin, or some signal on the board needs to be tapped that is fast enough to keep the WD happy, yet stops toggling when the system hangs.? Not something that is generally added after the fact. Also, there are system latchups that require a power cycle to clear.? The silicon structure can get an scr-like trigger from static zaps, rf, or whatever, and a reset will not clear it.? For a remote install, a timer cycling power at midnight is a pretty good plan, and easy to implement. gil ----- Original message ----- From: "vhsproducts via groups.io" <vhsproducts=[email protected]> Subject: Re: [TinyTrak] MT4BB Halting Date: Monday, October 18, 2021 5:31 AM The problem with having a TT4-based watchdog timer is that the ATMEGA chip seems to be the thing that hangs, so depending on the code to run in the chip that is locked up is a no-go. I have considered an extra timer based on a PIC to periodically restart the TT4 chip ( It does not take long to reboot)? so that it will still automatically essentially push the reset switch on pin 9 of the TT4 chip, and not be dependent on the TT4 itself. Compton's use of an external timer seems to validate the approach. I don't know if having a timer to intermittently reset the TT4 actually prevents the mysterious hanging condition, or if it just allows recovery in the rare instance of a hangup. 73, Allen AF6OF -----Original Message----- From: Barry L. Lankford <BarryL@...> Sent: Sun, Oct 17, 2021 11:08 pm Subject: Re: [TinyTrak] MT4BB Halting If you are OK with the fixed periodic reboot solution, the following might still be useful in the future.? Google "Watchdog Timer," the time-honored, last-ditch method of dealing with many impossible-to-find (and yet-to-be-experienced) bugs. I once took over a bad project where the original designer (and also its programmer) had included a watchdog function but put the code to periodically clear the watchdog counter inside an interrupt routine instead of in-line with the main program path.? So, when the main program somehow got out in the weeds, the timer service interrupt would push the "out in the weeds" program counter onto the stack, jam in the address of the interrupt service routine, which would then reset the timer preventing it from ever timing out.? The interrupt service code would then reach the end of the routine and the return from the routine would pop the old "out in the weeds" program counter location off the stack and the program would jump right back out into the weeds, solving NOTHING.? Don't do it that way! Unfortunately, AFAIK, we still don't have access to the source so it'd be difficult to add some elements of a watchdog timer function to the TT4 code.? I think there are some one-chip hardware watchdog timer solutions now.? Might be worth a look, but I've been out of that level of design for several years, so I'm not familiar with a lot of the newer ICs.? Maybe you could dead-bug the chip, connect it to suitable circuit nodes with wire-wrap wire and be done with it.? If "dead-bug" and "wire-wrap" are unfamiliar to the younger folks, Wikipedia them (wire-wrap is actually referenced in the wiki article about dead-bug). I think the techniques are still useful and the dead-bug method is very durable. Barry N4MSJ On 10/17/2021 9:10 PM, Compton wrote: > On Mon, Oct 18, 2021 at 12:45 PM, David Schultz, KC5WSV wrote: > >? ? Putting one of the problem systems in a location where it was easier >? ? to troubleshoot when it failed would probably help a lot. > > Done that. Found nothing. The timer work around works. Not worth > spending any more time on the issue. > > -- > Compton > VK2HRX > Sydney, Australia |
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