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v4linux & CameraPlugin

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timrowledge

v4linux & CameraPlugin

Is there anyone out there that actually feels they understand v4linux and how it is supposed to work with the CameraPlugin? At the moment, on a Pi, it works *once* but only once per run of squeak. The error message is
libv4l2: error setting pixformat: Device or resource busy
which seems to be a very common problem if you do a quick google. The problem is that it appears to have been common for a lot of people for a long time and many of the purported fixes make no sense to me at all. It doesn’t help that the code in the CameraPlugin/sqCamera-linux.c file doesn’t appear to fit in my head either.

Mind you, it does at least have the colours correct now; last time I managed to try it out (and I can’t recall whether it worked more than once back then, unfortunately) the RGB was more BGR.

tim
--
tim Rowledge; [hidden email]; http://www.rowledge.org/tim
On a clear disk you can seek forever...

Bert Freudenberg

Re: v4linux & CameraPlugin

On 08.02.2015, at 01:47, tim Rowledge <[hidden email]> wrote:
>
> Is there anyone out there that actually feels they understand v4linux and how it is supposed to work with the CameraPlugin?

Well, I suppose Derek (the original author) would have an idea. Cc'ed.

Also, v4l has an IRC channel and a mailing list:
http://www.linuxtv.org/lists.php

> At the moment, on a Pi, it works *once* but only once per run of squeak. The error message is
> libv4l2: error setting pixformat: Device or resource busy
> which seems to be a very common problem if you do a quick google. The problem is that it appears to have been common for a lot of people for a long time and many of the purported fixes make no sense to me at all. It doesn’t help that the code in the CameraPlugin/sqCamera-linux.c file doesn’t appear to fit in my head either.
>
> Mind you, it does at least have the colours correct now; last time I managed to try it out (and I can’t recall whether it worked more than once back then, unfortunately) the RGB was more BGR.

What camera are you using? Does it work with other software?

If it's the Pi-specific Camera Module then this might help:
http://www.raspberrypi.org/forums/viewtopic.php?f=43&t=50639

- Bert -

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Bert Freudenberg

Re: v4linux & CameraPlugin

Derek isn't subscribed to squeak-dev anymore, forwarding his reply:

Begin forwarded message from Derek O'Connell <[hidden email]>

>
> Hi Bert, Tim,
>
> the fact that it works once makes it smells like an "EINTR" problem. If
> you can "strace" to locate where it's occurring then it's simply a
> matter of wrapping it in a retry-loop. There will be other places where
> sys-calls are similarly wrapped (if not there then definitely in the
> ALSA/PA plug-in's and probably in the VM itself).
>
> In case you're not aware, a change in the Linux kernel several years ago
> dictated that anything could be interrupted at any time. I forget the
> details but it had a big impact on user-land code. It has took a long
> time for coders to adapt their code, not helped by the unpredictable
> nature of such interrupts and that there is no one-shot solution, hence
> some code could run for years without problem. To make matters worse you
> can end up plugging one bit of code only for EINTR to start popping up
> elsewhere. OTOH it seems insane to have to have to wrap every sys-call.
>
> Re camera code: std v4l code taken straight from examples plus
> non-circular buffering. Anything else can only be to do pixel formatting.
>
> Best wishes,
>
> -D

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timrowledge

Re: v4linux & CameraPlugin

In reply to this post by Bert Freudenberg

On 09-02-2015, at 8:36 AM, Bert Freudenberg <[hidden email]> wrote:

> On 08.02.2015, at 01:47, tim Rowledge <[hidden email]> wrote:
>>
>> Is there anyone out there that actually feels they understand v4linux and how it is supposed to work with the CameraPlugin?
>
> Well, I suppose Derek (the original author) would have an idea. Cc’ed.

Oh, of course. I even have his address from some ancient emails. D’oh.
>
> What camera are you using? Does it work with other software?

It’s the Pi camera. The interesting thing is that I’m *fairly* sure it used to (as in at least a year ago) work multiple times but the colour map was screwed.

tim
--
tim Rowledge; [hidden email]; http://www.rowledge.org/tim
The world is not magic