From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Steve DeRosier" <derosier@pianodisc.com>
Subject: RE: hw pause in USB
Date: Wed, 28 Dec 2005 15:37:44 -0800
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To: Takashi Iwai <tiwai@suse.de>
Cc: Clemens Ladisch <ladischc@informatik.uni-halle.de>, Alsa-Devel <alsa-devel@lists.sourceforge.net>
List-Id: alsa-devel@alsa-project.org

Ok, still on the hw pause issue.  I've got it so the "burp" doesn't =
happen any more. But upon unpause I'm still out of sync.  At first I =
just figured that my calculations based on delay were off, but at this =
point I think I'm right.

Here's the code:

            if( device.CanPause )
            {
              snd_pcm_pause(device.pcmhandle, 1);
            }
            else
            {
              /* more complex if we can't do hardware pause. */
             =20
              /* First step: get our count */
              device.PauseFrames =3D 0;
              err =3D snd_pcm_delay( device.pcmhandle, =
&device.PauseFrames );
              if( err )
                printf( "snd_pcm_delay error: %i\n", err ); =20
                 =20
              /* Second, drop the pcm data: */
              err =3D snd_pcm_drop( device.pcmhandle );
              if( err )
                printf( "snd_pcm_drop error: %i", err ); =20
             =20
            }
       =20
            all_notes_off();
            while (device.pause.status) {
              usleep(250000);
              start_time =3D time(NULL);
              update_status();
            }
           =20
            if( device.CanPause )
            {
              snd_pcm_pause(device.pcmhandle, 0);
            }
            else
            {
              /* More difficult to do a "software pause" */
             =20
              /* Get the data from our ring buffer */
              ogg_int16_t Buff[ RingBuff_Size( device.PauseBuff ) ];
             =20
              int PauseRet =3D RingBuff_GetBuff( device.PauseBuff, Buff, =
device.PauseFrames *2 );
             =20
              if( PauseRet < device.PauseFrames*2 )
                printf( "DSP Unpause: Frames stored !=3D frames =
returned.\n" );
             =20
               err =3D snd_pcm_prepare( device.pcmhandle );
               if( err )
                 printf( "DSP Unpause: snd_pcm_prepare return error: =
%i.\n", err );
             =20
              err =3D snd_pcm_writei( device.pcmhandle, Buff, =
device.PauseFrames );
             =20
              /* since the buffer should be empty, should never overrun. =
*/
              if( (err =3D=3D -EAGAIN) )
              {
                printf( "DSP Unpause: snd_pcm_writei return -EAGAIN when =
buffer should be empty.\n" );
              }
              else if( err < 0 )
              {
                printf( "DSP Unpause: snd_pcm_writei return < 0: %i\n", =
err );
              }

Note, RingBuff_* has been tested to work and returns what I'm asking of =
it. It handles 16bit words, and since a frame (in this config anyway) is =
two 16 bit words I'm having to mult frame counts by 2 when I work with =
it.  When I do my snd_pcm_writei() calls earlier, I always then put the =
same data into the ring buffer so it is always full of the most current =
data I did via snd_pcm_writei().

Any sugestions?   =20

Thanks,
- Steve



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