General: A simple as possible 4 cylinder ODB-II ECU?

[GreenBrick]

As it runs Linux, I guess you would need a custom kernel to be able to react to all the inputs and send outputs when you want them, rather than when the OS decides.

We tried to use embedded linux in a video recorder and had a lot of trouble with critical timings.

It may be possible, but the work involved would be far more complicated.

(I could be completely wrong, the wife thinks I am most of the time, but having talked to people who know far more about these things than I do, the Raspberry PI is not one to use).

[Army]

I don't know which processors / operating systems would be best but I guess they are pretty low tech. You've got a mechanical system that operates in a speed range between 0 and say 7000rpm = equivalent frequency range (cycles per second) => 0 to 167 Hz

Double that and add on a bit of extra bandwidth for anti-aliasing filters (which probably don't get used as I suspect it is probably lazy cheap as chips digital signal processing) and you've got to have something that can sample say ten things at a rate of at least 400Hz - a little bit of decision making and two output signals per cycles (for a four cylinder engine) might mean you need a system that needs a 5kHz processor...

...I don't think (non Microsoft) computers are made that slow any more!

EDIT - there is probably the need for a little bit more decision making - more of the IF this THEN that - so processor clock speeds might need to be a bit higher

[rippedoffagain]

Originally Posted by GreenBrick

As it runs Linux, I guess you would need a custom kernel to be able to react to all the inputs and send outputs when you want them, rather than when the OS decides.

We tried to use embedded linux in a video recorder and had a lot of trouble with critical timings.

It may be possible, but the work involved would be far more complicated.

(I could be completely wrong, the wife thinks I am most of the time, but having talked to people who know far more about these things than I do, the Raspberry PI is not one to use).

Fair point. I hadn't considered that but I think you're right.

Linux has an interesting approach to input and output. Everything is basically a file stream. As such, when you write to it, you're basically telling the OS to write it out, sort of whenever you get a moment like. It won't be forever, but it depends when the scheduler gives focus to the task of doing the right. On some Linux installs it could be 20 milliseconds. I'd have to do some sums but my gut instinct tells me it wouldn't be responsive enough.

Processing speed wouldn't be an issue. It's a surprisingly capable cpu in the pi. It's just IO that might be the problem.