[-,JACK,PCM,plugin] jack: Use boundary as hw_ptr wrap around

Commit Message

Timo Wischer Feb. 9, 2018, 1:11 p.m. UTC

Hello all,

[1] was merged as it is (see [2])
Therefore this commit can be merged without conflicts, now.

Please have a look.

[1] http://mailman.alsa-project.org/pipermail/alsa-devel/2018-January/130942.html
[2] http://git.alsa-project.org/?p=alsa-plugins.git;a=commit;h=21839e981a4b7c7178c1a473f20460c003e13db4

Best regards

Timo Wischer

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Patch

diff --git a/jack/pcm_jack.c b/jack/pcm_jack.c
index 3aed332..c22a5d0 100644
--- a/jack/pcm_jack.c
+++ b/jack/pcm_jack.c
@@ -40,6 +40,7 @@  typedef struct {

        char **port_names;
        unsigned int num_ports;
+       snd_pcm_uframes_t boundary;
        unsigned int hw_ptr;
        unsigned int sample_bits;
        snd_pcm_uframes_t min_avail;
@@ -130,6 +131,21 @@  static int snd_pcm_jack_poll_revents(snd_pcm_ioplug_t *io,
 static snd_pcm_sframes_t snd_pcm_jack_pointer(snd_pcm_ioplug_t *io)
 {
        snd_pcm_jack_t *jack = io->private_data;
+
+       /* ALSA library is calulating the delta between the last pointer and
+        * the current one.
+        * Normally it is expecting a value between 0 and buffer_size.
+        * The following example would result in an negative delta
+        * which would result in a hw_ptr which will be reduced.
+        *  last_hw = jack->boundary - io->buffer_size
+        *  hw = 0
+        * But we cannot use
+        * return jack->hw_ptr % io->buffer_size;
+        * because in this case an update of
+        * hw_ptr += io->buffer_size
+        * would not be recognized by the ALSA library.
+        * Therefore we are using jack->boundary as the wrap around.
+        */
        return jack->hw_ptr;
 }

@@ -162,7 +178,7 @@  snd_pcm_jack_process_cb(jack_nframes_t nframes, snd_pcm_ioplug_t *io)

        while (xfer < nframes) {
                snd_pcm_uframes_t frames = nframes - xfer;
-               snd_pcm_uframes_t offset = hw_ptr;
+               snd_pcm_uframes_t offset = hw_ptr % io->buffer_size;
                snd_pcm_uframes_t cont = io->buffer_size - offset;

                if (cont < frames)
@@ -176,7 +192,8 @@  snd_pcm_jack_process_cb(jack_nframes_t nframes, snd_pcm_ioplug_t *io)
                }

                hw_ptr += frames;
-               hw_ptr %= io->buffer_size;
+               if (hw_ptr >= jack->boundary)
+                       hw_ptr -= jack->boundary;
                xfer += frames;
        }
        jack->hw_ptr = hw_ptr;
@@ -200,6 +217,8 @@  static int snd_pcm_jack_prepare(snd_pcm_ioplug_t *io)
        err = snd_pcm_sw_params_current(io->pcm, swparams);
        if (err == 0) {
                snd_pcm_sw_params_get_avail_min(swparams, &jack->min_avail);
+               /* get boundary for available calulation */
+               snd_pcm_sw_params_get_boundary(swparams, &jack->boundary);
        }

        /* deactivate jack connections if this is XRUN recovery */