Re: pause(.01) gives a mean pause of 0.0102 and not 0.0100 seconds

[Przemek Klosowski]

On 10/16/19 4:47 PM, GoSim wrote:
> I use octave as a real time controller and use pause() to get my desired
> sample time. When I want to get a sample time of 0.01 seconds I get a mean
> pause of 0.0102 seconds. I tried pause(0.0100000) with the same result. I
> don't know if it is fixable or if it is a bug but I just wanted to make you
> aware.
>
> I attach a picture with the sample time in a real time environment and you
> can also see the command
> tic;pause(.01);toc in the octave console giving the same result.
>
> The real time environment is achieved with the chrt command in xubuntu.
>
> The graph in the pic shows the sample time which should 0.01 seconds.
>
> I hope you fix it! Kind regards.
I am actually quite impressed how good it is!

I don't think it's realistic to expect much better results. Note that 
tic;command;toc measures the time to execute the command PLUS half of 
the time to execute the pair tic; toc. The occasional deviation is also 
quite hard to avoid, and is not really Octave's fault---it has to do 
with the inherent timing variations in all the components of your 
system, from CPU and the memory subsystem to all the peripherals, and 
various data management functions in the interpreter.

No milisecond-resolution real time loops in interpreted languages, I'm 
afraid. My advice would be to rewrite your code to run the realtime loop 
in a dedicated process compiled from say C, that is sharing data with a 
separate Octave process.