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

katja katjavetter at gmail.com
Wed Dec 3 03:20:49 CET 2014

Let me reformulate the mystery: one pd executable is able to get real
time priority while another is not, on the same system and started by
the same user belonging to group audio.

Raspbian is now indeed distributed with real time priority set by
default for audio group (thanks Chris for pointing that out), with
user pi as member of audio group. These are the settings which should
give real time priority for pd.

But the point is, these settings do not work for a 'local install'
like when you put a build from Miller's site in your home dir, even
while you do get real time priority for puredata when installed from
Raspbian repository, or Pd-extended from apt.puredata.info.

There's good reason to use Miller's latest build on Raspberry Pi.
Puredata is debian-packaged vanilla, and wheezy has an outdated
version (0.43). For one thing, that version doesn't handle subnormals
properly on armv6, which may under certain conditions eat all CPU
time. Miller has fixed that almost two years ago. With puredata 0.46.2
from jessie, you have best of both worlds: real time priority and no
subnormals bug. However Raspbian jessie is not yet released.

Following IOhannes' guidelines in an earlier thread I built the .deb
packages from jessie source. That works great, but still it's quite a
detour and in particular for new users there should be an easier way
to get pd working properly on Raspberry Pi. If there's a trick to get
real time priority for a build in home directory (apart from running
as root), that would be great. I've always wondered, how does the
system know that puredata is an audio process? Maybe that's where it
goes wrong with the local build?


On Tue, Dec 2, 2014 at 7:36 AM, Chris McCormick <chris at mccormick.cx> wrote:
> On 02/12/14 14:20, Chris McCormick wrote:
>>> 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...
>> Is this something that is set in /etc/security/limits.conf? That file is
>> empty except for comments.
> pi at razor ~ $ cat /etc/security/limits.d/audio.conf
> @audio   -  rtprio     95
> @audio   -  memlock    unlimited
> #@audio   -  nice      -19
> So it looks to me like it has the right realtime settings by default.
> Cheers,
> Chris.
> --
> http://mccormick.cx/

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