[PD] Raspberry Pi & pd 0.46 with real time priority

[Miller Puckette]

Hi all -

The following magic seems to work on any linux distribution: edit
/etc/security/limits.conf and add the lines,

* - rtprio 99
* - memlock 1000000000

I can't remember if I did this on my Pi or not (and don't have it handy
right now to check) but I bet I did.

On the other hand, I wonder what Pd extended does.  Perhaps it makes itself
belong to group 'audio' and runs 'rwxr-sr-x' (the 's' meaning that it
confers its group status to whomever runs it).  But I thought the 'pi'
user was already part of group audio.  Also I'm not sure if group audio
gets realtime permission by default on Raspian - that's another thing I'd
need to dig up my pi to check...

cheers
Miller

On Sun, Nov 30, 2014 at 03:12:10PM +0100, katja wrote:
> Without real time priority, Pd on Raspberry Pi easily suffers from
> drop outs. When I run vanilla Pd (for example 0.46-2 executable from
> Miller's site http://msp.ucsd.edu/software.html) on Raspbian with
> option -rt, it says that priority scheduling failed, and 'audio I/O
> error' flashes whenever I move the cursor (I'm not running the Pi
> headless).
> 
> I've noticed that puredata 0.43 as installed from Raspbian repository
> can run with real time priority even when started by normal user. I
> wondered where the difference is: in the Pd version or in the fact
> that puredata from repository is installed and owned by root. Or maybe
> yet another factor that I can't think of. In any case, I built and
> installed puredata 0.46.2 from repository source (described here:
> http://lists.puredata.info/pipermail/pd-list/2014-11/108543.html).
> This build works with normal user real time priority too.
> 
> In order to see if ownership matters, I changed ownership of Miller's
> build to root. Still it can't run with real time priority when loaded
> by normal user. Permissions are the same for Miller's build and
> puredata from repository (-rwxr-xr-x).
> 
> Does anyone know a way to run Miller's build with real time priority
> (apart from running with root permission, which I don't want)? Though
> I'm happy with puredata 0.46.2 as built from repository source, there
> may sometimes be a reason to use or test another build.
> 
> Katja
> 
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