Re: Raspberry Pi, Real-Time and Ada

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On Thu, 06 Feb 2014 01:50:40 -0600, Stephen Leake wrote:

> "Rego, P." <pvrego@gmail.com> writes:
> 
>> Is it possible to run Real-Time applications on Raspberry Pi
>> (specially in Ada)? Yesterday I began to read the RPi documentation,
>> and discovered that several (actually all that I found) I/O libraries
>> available to access GPIOs (mostly written in C and Python) are not
>> Real-Time, and even the Raspbian Debian distribution is not intended
>> to run RT applications, so it's not built for it.
> 
> You seem to be using "Real-Time" in some special technical way, as
> opposed to the general definition "meeting the application timing
> deadlines".
> 
> Using the general definition, if your application has deadlines with
> tolerances on the order of 0.1 seconds, then the answer is clearly
> "yes".
> 
> For tighter tolerances, you'd have to measure the actual performance,
> and possibly use an enhanced kernel as you discussed.

Absolutely.

Last time I checked there were ARM GPIO drivers for Linux, so I see no
problem with RT except for possibly poor performance of the GPIO.

It really depends rather on the hardware than the OS. In particular on how
many AD/DA converters are physically present (to be shared between analogue
inputs).

Note that if you have, say, one AD multiplexed to four inputs, then no
matter how RT your OS is, the latency between 1st and 4th inputs will be no
less than 4 conversion times. Taking typical values 40us * 4 = 0.8ms. Now
if inputs considered synchronous, this is also the jitter.

BTW, many boards do not even have all GPIO pins soldered. You should check
if Raspberry Pi has ones you wanted to use.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de