60 hz timer

Hi all, I've become quite frustrated with a problem and so I seek help from the powerful minds that congregate here. ;)

The main device I work on has a large COTS piece of hardware that operates, and sends us packets, at 60hz. We use these incoming packets as a timer for a large number of processes.

Recently we developed a stripped down device for our customer that offers 75% capability at 20% of the price. One of the things to get cut was this hardware that sends us packets at 60hz.

Because we no longer have a hardware timer I attempted to write a 60hz software timer(using QueryPerfromanceCounter() and the like). This works great on my desktop, unfortunately the machines in the device are both slower and running a lot of processes which causes the software timer to be slow by about 8 seconds per hour.

So now I'm searching for cheap hardware solution. I know they exist, I just can't figure out the proper search phrase(I've been looking on and off for a bout a month). Does anybody know of a simple device that can output a signal to RS-232 at 60hz?

Thanks!

At first glance I think you could take a power cord off an appliance like a toaster, strip the ends of the wires, and attach to a cat. The cat will meow 120 times per second (one meow for each of the positive/negative peaks of the AC waveform). Using a microphone, attach to an ADC and digitize, then process digitally to remove every other meow. The resulting meows will be at a frequency of 60 hz.

EDIT: Ugh, I just realized that this may make your device too expensive, since shipping of a live cat is not cheap and food must be provided. Depending on which TI ADC you choose (you DO buy only TI components for DSP, right) that may be another added cost. Hmm. I'll try to think of something cheaper.

Okay, okay. Obviously I'm joking. The serious point I am obscuring with this stupidity is that the power itself will be at 60 hz (if you're American, at least) and you MAY be able to use this somehow.

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Originally Posted by brewbuck

EDIT: Ugh, I just realized that this may make your device too expensive, since shipping of a live cat is not cheap and food must be provided. Depending on which TI ADC you choose (you DO buy only TI components for DSP, right) that may be another added cost. Hmm. I'll try to think of something cheaper.

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Not to mention, this will be used on an Army base, and those guys like to walk off with piece of the units. Probably wouldn't go over so well to have to keep replacing cats.

(also, the smell...)

A serial port server perhaps?
Here

meow! love it. the link brewbuck put up send packets at 802.11gb not 60 hz. something more like a 555 timer chip would give you 60 hz. connect it to the clk pin on your rs232.

a meowtrakngome

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Originally Posted by kryptkat

something more like a 555 timer chip would give you 60 hz. connect it to the clk pin on your rs232.

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This is closer to what I was looking for, although I doubt the management would like the idea of building this in house(They would much rather buy COTS or sub-contract). Any chance there's an existing product using these?

This is why I love programming.

The 555 is a good way to go if your power is not guaranteed to be 60hz (but if military and using oseas power lines they tend to be 50hz; I had serious problems in Germany in the 80s w/systems that derived clock from power). And the 555 is both harder to walk off with and cheaper than a cat.

Or just run it through a comparator (the other terminal to ground). Why would you need to sub-contract someone for that?

Come to think of it, 555 is probably a better idea.

Only needs DC (just draw it from any of the internal power supply lines).

But this should be doable in software.

You can make it "self-correcting".

After each wait, subtract the extra time from the next wait.

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And the 555 is both harder to walk off with and cheaper than a cat.

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hey ! i am a parsh kitten.

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Come to think of it, 555 is probably a better idea.

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thank you.
you should be able to run it off of your computers +5v power supply. do not remember if rs232 has a pos +5v line or not. one thing you may run in to is power leveling <amps> or in this case micro amps. impedance match a must.

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Originally Posted by kryptkat

meow! love it. the link brewbuck put up send packets at 802.11gb not 60 hz.

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Brewbuck didn't post that link. I did.

oops.

Problem with RS-232 is that it requires a negative voltage for low, and the port doesn't supply power. Since all the power supply lines in a computer probably have a common ground, you cannot just connect 2 together to get the negative voltage. Meaning you'll probably need to get power from outside, with your own transformer.

> unfortunately the machines in the device are both slower and running a lot of processes which causes the software timer to be slow by about 8 seconds per hour.
But you were using QueryPerformanceCounter?
Also bear in mind that QPC could give some very odd results if the processor is variably clocked (as in a laptop) to save power.

What exactly is your embedded device?
If it's running processes, then that implies a scheduler of some sort as well. Unless the scheduler is entirely cooperative, having a hardware timer interrupt is all but essential.

Having found the hardware timer, is that stable for your needs?

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Originally Posted by cyberfish

Meaning you'll probably need to get power from outside, with your own transformer.

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Make sure you wear insulated gloves for this Dr. Frankenstien -- someone might get hurt.

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Originally Posted by Salem

> unfortunately the machines in the device are both slower and running a lot of processes which causes the software timer to be slow by about 8 seconds per hour.
But you were using QueryPerformanceCounter?
Also bear in mind that QPC could give some very odd results if the processor is variably clocked (as in a laptop) to save power.

What exactly is your embedded device?
If it's running processes, then that implies a scheduler of some sort as well. Unless the scheduler is entirely cooperative, having a hardware timer interrupt is all but essential.

Having found the hardware timer, is that stable for your needs?

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That's quite a good suggestion. We're actually running servers with Quad-core opterons, and after a bit of reading it looks like AMD implemented "Independent Dynamic Core Technology" which clocks each core independently. I'm going to check out if disabling that helps anything. Thanks!

As for the hardware timer. I'm now trying to devise a software side solution for syncing to a signal over RS-232. The existing implementation is to use ReceiveFrom() to sync via UDP without constantly polling. Anybody know of a similar functionality for RS-232?

I'm guessing you've got an OS on top of that lot?

So which is it?