Auto run 2 different programs at boot

[dukenukem]

Hi everybody,
I would like to use a Raspberry Pi in an embedded way in a project: the Raspberry has to auto-run two C programs at boot and periodically (every 50/100ms) run those programs, for its entire life.

What is the best way to do so?

I am able to auto run programs at boot modifying the rc.local file , but this will execute those program only once. How to periodically execute them?

In addition, one of those C program should be activate only when an interrupt is detected on a GPIO pin. Is it possible to obtain this behaviour?

Thank you!
Tommaso

[RaTTuS]

every 50 / 100 ms is pretty damn fast ...

but if you have a script that calls your stuff like
#!/bin/sh
while [ 1 ] ; do
/home/pi/proggy
done

then that will run for ever

you can use interrupts to select your code etc....

[ghans]

How much jitter is acceptable to you ? Can you deviate from the 50/100 ms interval ?

ghans

[dukenukem]

Well every 50ms a pin is raised from a micro controller to a GPIO pin of the Raspberry, this pin should generate an interrupt in the Raspberry (that in the meantime is running the other C program) and they should communicate in SPI (this communication lasts for about 2 ms), subsequently this data has to be elaborated but in very simple way, so i think it won't take much time.

The other program should be executed every 100ms but this is not a strict obligation, a 200/300ms period is ok.

For the 50ms interrupt i am now reading some infos about the wiringPi library, i think it should work, doesn't it?

Another way could be a 'concurrent' execution of these 2 programs and the first one reads that pin in a polling way, but i am afraid this could decrease too much the entire system speed.

[topguy]

Why cant the program just run continuously and do its stuff when it needs to, you can control timing much better from inside a running program.

- When should I do stuff: T2
- What the time now: T1
- Lets wait: T2 - T1
- do stuff.

And the other process handling the GPIO interrupt could in theory run in a seprate thread in the same program.

[kusti8]

Two ways: in the script, use sleep to pause until you do it again. The other way is to use crontab, but that has a minimum of 1 second. I recommend the first.

[dukenukem]

I have no experience in this field but it seems to me that two feasible ways to run two application in a concurrent way are:

1) a shell script that periodically calls those programs. Here i don't get how to handle the interrupt wake up of one program and the periodic execution of the other (is it possible to use a timer in a shall script?????).

2) the other way is writing an entire program with multiple threads. I suppose it is the easiest and faster way but, what i don't like of this solution is the fact that those 2 programs have nothing in common, they don't share any variable, so i would like to keep them separate.

Does it make sense what i have said? Are there other solutions?

[RaTTuS]

personally,
for interrupts - I'd have the program running all the time and act on those interrupts to do what it needs to do
for the other that just runs periodically then depending on what it neds to do and how often and to what degree of accuracy
cron has a 1 minute min period
anything shorter then you need to either loop a script - with suitable delays
or write a program that does it .

[ghans]

Don't use a script , but a third program to spawn the others - a C program should give you much better control than a Bash script.

ghans