How to choose a firmware partner

How do you know if you have the optimum distribution of

clear-WDT

instructions?

If your system is simple enough to predict this, then it is simple enough to code without the risk of depending on state to avoid lockup.

If your system is too complicated to predict optimum distribution then you must err on the safe side allowing bugs to remain undetected because they are masked by watchdog resets.

Yes we do this, without problems. Our code is inherently safe. This is easy to do because it is small.

I was afraid someone would say that.

Robin

Yes, I did consider that for a moment, but then the Troll-o-meter kicked in, as it did on the first post. -jg

systems run

Absolutely - I (or rather my daughter) is adept at this. Set-top boxes seem to be particularly bad, and I believe I know why...

Steve

Untrue.

I've used watchdogs (external hardware watchdogs, i.e. cannot be disabled) in systems with a single 8-bit CPU, 128 bytes of RAM, and under 2k of ROM.

Again, you're missing the main point of using a watchdog. It's nothing to do with software.

Steve

Forgive my ignorance (I was released 1970), what is the difference between core and RAM chips ?

In article , " snipped-for-privacy@tesco.net" writes

So you've never run code on a standalone MCU in an electrically noisy environment then?

Do tell. (I can crash my set top box in about 10 seconds without even trying. Luckily it has a power switch on the front).

Robert

Wow, do I feel old now. Magnetic core was a bunch of tiny little "donuts" that looked something like miniscule ferrite beads. It was literally sewn together by meticulous women (peering thru microscopes) into an X, Y type lattice that also had a sense/inhibit wire running throughout all the "donuts". Each little donut could be magnetized into one of two polarities to represent a 1 or 0. When core was read, it destroyed the data stored and had to be automatically rewritten by the hardware. Some guy named Wang figured all this out.

;-)

Cool, it's nice to meet someone that actually worked with this stuff before. I was beginning to think that everyone who had was dead now, or worse yet French. ;-)

seem

Brief version: this area seems to suffer from the Curse of The Inappropriate RTOS. Or perhaps it's appropriate, due to all the various 3rd-party comms layers required... but in any case, said RTOS doesn't seem to cope with processing key events terribly fast. Which seems kinda lame.

The longer version involves the amount of times I've talked myself out of a job with set-top box manufacturers.

Steve

Huh? Why French?

Steve

These were Varian (later Sperry, then SSCI) machines. The originals could handle only 64 MB, as I recall. Our earlier systems sometimes shipped with less than that. Later, they introduced the "Megamap" which extended addressing capability to a megabyte by use of page mapping registers. I don't remember when the Megamap was introduced. It might not have been until the V-70 series.

That explains your statement, I guess, but you misunderstand the purpose of the watchdog. It's not to protect against coding errors. Hardware breaks.

Are you referring to a Sky digibox by any chance? I have to reboot mine at least twice a week.

Andy

Anthony gave a good description. Keep in mind that many of us old farts have a tendency to call even semiconductor memory "core." In fact, crash dumps are still called core dumps even by people who never saw any core .

There are interesting pictures at

among others.

I remember when core prices finally were reduced to the long anticipated goal of a penny per bit.

One of the good features of core was that it was non-volatile. In the early days of semiconductor memory, it was a hard sell in the process control industry because it would lose it's data if the power went down. We sold battery backed up memory because of this. Still, it was somewhat unreliable, so all our memory was ECC, self-correcting for

No kidding. Did anyone else have the high school algebra book that had a picture of a core plane on the cover? Latest technology then.

Magnetic core was a bunch of tiny little

Back in 1985 I had an interview at one of the last places that still made core memory (there was still military gear being built with core). It was pretty impressive in a retro sort of way. The toroids looked like rounded black grains of sand. The holes in the middle were not casually visible to the naked eye: if you knew the holes were there you could just barely see them under just the right lighting. Once woven together, a sheet of the things looked like a shiny, coarsely woven fabric.

The place only had a couple women capable of stringing the beads. They were a bit worried that one of them would quit or die or whatever before they EOL'ed the product, since finding/training a new person was quite time-consuming.

seem

I've had a Sky box, and yes, it was fragile. I was actually referring to my Nokia freeview receiver - which my daughter (she of the phn txt skl) manages to crash in seconds.

Steve

Indeed.

To Robin: more saliently, it also gets zapped - non-destructively, but enough to cause it to go "off in the weeds". See post re electrically noisy environments. CE marking etc be damned - not too much one can do about this kind of noise (including care in ground plane design - yawn - which is a given, I'd thought) except detect the effects and recover.

As another poster said, designing embedded systems (esp. unattended systems) without a watchdog is tantamount to driving without insurance. This isn't a matter of opinion, it's a matter of hard-won experience.

Steve