Thread: [Alsa-user] Direct memory write for more than 4 channels

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> Hi,
>
>
>
> I’m having difficulty getting more than 4 playback channels to work using
alsa callbacks and direct memory write.
>
>
>
> The sound card is an RME HDSP Madi, and alsa version is 1.0.15. I’m
currently forced to use this old version as having problems with later alsa
and the RME card (long story). The Madi is running in double-speed mode so
supports 32 channels at 96k bps.
>
>
>
> Currently the code works fine for record on all 32 channels.
>
> Previously I only output on the last 2 channels 31 & 32, which is the
stereo output on the PCI card itself. The output code worked fine.
>
>
>
> I’m now attempting to output on multiple channels using and external 8
channel in/out box on the fibre Madi.
>
> The 1st 4 channels work OK if I use slot ID 1, but 5th and higher do not.
Also strange pulsing noises appear on other channels (eg 31,32).
>
>
>
> I’m baffled. As I understand it, all channels work synchronously, so they
all should have the same number of frames free to write to in the ring
buffer at the same time.
>
> If I set the ID to 2, I can’t get channel 8-16 to work at all.
>
>
>
> My code looks like this:
>
> Callback:
>
> <handle record buffers>
>
> size = period_size;
>
> snd_pcm_avail_update(outhand);
>
>         while (size > 0) {
>
>             frames = size;
>
>             err = snd_pcm_mmap_begin(outhand, &my_areas, &offset,
&frames);
>
>             <error handling>
>
>             load_output(my_areas, offset, frames, (PCMDATA *)data);
>
>             commitres = snd_pcm_mmap_commit(outhand, offset, frames);
>
>             <error handling>
>
>             size -= frames;
>
>         }
>
>
>
> static void
>
> load_output(const snd_pcm_channel_area_t *hard,
>
>            snd_pcm_uframes_t offset,
>
>            int count, PCMDATA *tx)
>
> {
>
>                 frame_t *outp[MAXCHCH], *hwp[MAXCHCH];
>
>                 frame_t *psave[MAXCH];
>
>                 int y;
>
>
>
>                 for(y=0; y < tx->hwchans; y++)
>
>                 {
>
>                                 psave[y] = (frame_t *)((unsigned char
*)hard[y].addr + (hard[y].first/8)) + offset;
>
>                 }
>
>              <fill required psave channels directly with my pcm data from
tx>
>
> }

Thread: [Alsa-user] Direct memory write for more than 4 channels

alsa-user