[alsa-devel] Fwd: ALSA queries
Chakravarthi Pradeep
doubleq7 at gmail.com
Mon Aug 6 14:29:26 CEST 2018
Hello Takashi,
Thanks for your explanation about period and periods.
> Erm, I'm no consultant. Does your driver issue really
> snd_pcm_period_elapsed() or not? You should know that.
>
> If the problem happens even if the driver really calls
> snd_pcm_period_elapsed(), then it's another cause
I'm calling snd_pcm_period_elapsed() in my audio thread
snd_pcm_period_elapsed(drv->substream);
I'm calling this <snd_pcm_period_elapsed()> function after one frame
is copied to from PCIe device. However, hwptr is not updated and no
sound in the VLC application.
Regards,
Chakravarthi Pradeep K
On Mon, Aug 6, 2018 at 2:09 PM Takashi Iwai <tiwai at suse.de> wrote:
>
> On Sun, 05 Aug 2018 20:09:47 +0200,
> Chakravarthi Pradeep wrote:
> >
> > ---------- Forwarded message ---------
> > From: Chakravarthi Pradeep <doubleq7 at gmail.com>
> > Date: Sun 5 Aug, 2018, 14:19
> > Subject: Re: [alsa-devel] ALSA queries
> > To: <tiwai at suse.de>
> >
> >
> > Hello Takashi,
> >
> > Thanks for your reply.
> >
> > periods_min = the minimal number of periods
> > period_bytes_min = the minimal size of bytes for one period
> > period_bytes_max = the maximal size of bytes for one period
> >
> >
> > periods_min = the minimal number of periods : what is meaning of
> > periods , is it minimal number of interrupts ?
>
> The "period" in ALSA PCM definition represents the interval time (or
> frames) of the periodical interrupts on the ring buffer. If the irq
> is issued for each 256 frames while the ring buffer size is 1024
> frames, periods = 1024/256 = 4. The periods_min defines the minimal
> number of periods the hardware may accept.
>
> > period_bytes_min = the minimal size of bytes for one period : it
> > means, minimal size of bytes per interrupt in case of device, Is it
> > correct ?
>
> Correct.
>
> > what about period_max ?
>
> The maximal number of periods, the counter-part of periods_min.
>
>
> > It's most likely the ALSA PCM core's safety stop; your driver seem to
> > have missed snd_pcm_period_elapsed() calls, so the hwptr isn't
> > updated, resulting in XRUN. ALSA PCM core checks such XRUN condition
> > with the own timer.
> >
> > I'm attaching my driver thread along with this mail. Can you please
> > let me know if I have missed something in audio thread. ?. How to make
> > sure in driver that, trigger stop should be called only when stop
> > command is sent from application.
>
> Erm, I'm no consultant. Does your driver issue really
> snd_pcm_period_elapsed() or not? You should know that.
>
> If the problem happens even if the driver really calls
> snd_pcm_period_elapsed(), then it's another cause.
>
> > I'm getting cut cut cut ... noise along with audio in VLC application.
> > Initially for 2 or 4 seconds, cut cut cut noise is not heard in VLC
> > application, However after almost after 5 sec ,I can hear cut cut cut
> > noise in VLC application. With my analysis, hwptr is getting updated
> > properly however I have doubt in app_ptr. I'm attaching the excl sheet
> > with hw_ptr,app_ptr and buf_pos values.
>
> Do the buffer size and period size are set really as expected?
> Often the driver misses the fact that PCM core doesn't guarantee the
> alignment of buffer size and period size unless specified explicitly
> via hw constraints. That is, as default, it's possible to set a
> buffer size 3000 bytes for the period size 64 bytes. Then the last
> period is partial.
>
> For aligning the period and the buffer sizes, call
> snd_pcm_hw_constraint_integer(runtime, SNDRV_PCM_HW_PARAM_PERIODS);
> in the open callback.
>
>
> Takashi
>
> >
> > How to remove the cut cut cut ... noise in audio ?
> >
> > Regards,
> > Chakravarthi
> >
> > On Fri, Aug 3, 2018 at 1:05 PM Takashi Iwai <tiwai at suse.de> wrote:
> > >
> > > On Thu, 02 Aug 2018 16:31:13 +0200,
> > > Chakravarthi Pradeep wrote:
> > > >
> > > > I'm working on ALSA driver for PCIe card. My ALSA driver and it's
> > > > initializing struct snd_pcm_hardware with below parameter.
> > > >
> > > > /************************ code start
> > > > ************************************************/
> > > > static struct snd_pcm_hardware audio_pcm_hardware = {
> > > > .info = (SNDRV_PCM_INFO_INTERLEAVED | SNDRV_PCM_INFO_MMAP |
> > > > SNDRV_PCM_INFO_MMAP_VALID |
> > > > SNDRV_PCM_INFO_BLOCK_TRANSFER |
> > > > SNDRV_PCM_INFO_RESUME ),
> > > > .formats = (SNDRV_PCM_FORMAT_S16_LE | SNDRV_PCM_FORMAT_S24_LE),
> > > > .rates = (SNDRV_PCM_RATE_44100 | SNDRV_PCM_RATE_48000 |
> > > > SNDRV_PCM_RATE_96000 | SNDRV_PCM_RATE_192000),
> > > > .rate_min = 44100,
> > > > .rate_max = 192000,
> > > > .channels_min = 2,
> > > > .channels_max = 8,
> > > > .buffer_bytes_max = 76800, /*75 kbytes */
> > > > .period_bytes_min = 512,//4410, /* (channel (2) * sample_rate (44100)
> > > > * bit width (24)) / (60 * 8) */
> > > > .period_bytes_max = 16*1024,
> > > > .periods_min = 10,
> > > > .periods_max = 255,
> > > >
> > > > };
> > > > /************************ code end
> > > > ************************************************/
> > > >
> > > > 1) I did not understand what is significance of periods_min ,
> > > > period_bytes_min , period_bytes_max and periods_max. Can you please
> > > > tell me what is importance of these parameter and what value should be
> > > > mentioned according into ALSA.
> > >
> > > These three defines the values your hardware may accept:
> > > periods_min = the minimal number of periods
> > > period_bytes_min = the minimal size of bytes for one period
> > > period_bytes_max = the maximal size of bytes for one period
> > >
> > > > 2) snd_pcm_ops trigger callback is getting called in the driver when
> > > > application sends "start" command. But ALSA driver is stopping by
> > > > itself after one frame is copied to ALSA framework, without waiting
> > > > for "stop" command.
> > > >
> > > > For instance:
> > > > In trigger callback , I'm getting these logs after one frame is copied.
> > > > Trigger:Start (When Play button is selected/clicked in application,
> > > > Start command is sent to ALSA driver)
> > > > Dma transfer is completed.
> > > > Trigger:Stop. (When Stop button is selected/clicked in application,
> > > > Stop command is sent to ALSA driver. But stop button is not clicked in
> > > > this case)
> > >
> > > It's most likely the ALSA PCM core's safety stop; your driver seem to
> > > have missed snd_pcm_period_elapsed() calls, so the hwptr isn't
> > > updated, resulting in XRUN. ALSA PCM core checks such XRUN condition
> > > with the own timer.
> > >
> > >
> > > Takashi
> >
> >
> >
> > --
> > Thanks and Regards
> > Chakravarthi Pradeep.K
> > Ph: 91 9980434900
> > [1.2 <text/html; UTF-8 (quoted-printable)>]
> >
> > static int uhdc_audio_thread(void *data)
> > {
> > char *audio_frame = NULL;
> > int count = 0;
> > uhdc_t3_card_driver *drv = (uhdc_t3_card_driver *)data;
> > struct snd_pcm_runtime *runtime = drv->substream->runtime;
> >
> >
> > audio_frame = kmalloc(MAX_AUDIO_SIZE, GFP_DMA);
> > if(!audio_frame)
> > {
> > return -ENOMEM;
> > }
> > while(1)
> > {
> >
> > if (kthread_should_stop())
> > {
> > dbg_alsa( "###### %s %d\n",__FUNCTION__,__LINE__);
> > break;
> > }
> > dbg_alsa( "###### Waiting for audio signal %s_%d\n",__FUNCTION__,__LINE__);
> > wait_event_interruptible (audio_interrupt, (atomic_read (&audio_data_ready)));
> > atomic_set (&audio_data_ready, 0);
> > g_count = get_audio_size(g_temp_lro);
> > count = g_count;
> > printk( "######audio signal received and audio size:%d runtime->period_size:%d %s_%d\n",g_count,runtime->period_size,__func__,__LINE__);
> >
> > /* dma read is done here */
> > /* audio_frame contains audio data */
> > memcpy(drv->substream->runtime->dma_area + drv->buf_pos ,audio_frame,count);
> >
> > /* update the buf_pos */
> > // here the (auto)increase of buf_pos is handled
> > drv->buf_pos += count;
> > drv->buf_pos %= drv->pcm_buffer_size;
> >
> >
> > printk("\n\n\n hwptr=%d appl=%d pos=%d\n",
> > (int)frames_to_bytes(runtime,runtime->status->hw_ptr),(int)frames_to_bytes(runtime, runtime->control->appl_ptr),drv->buf_pos);
> > /* Below line needs to be uncommented for pointer to be updated in the alsa lib */
> > snd_pcm_period_elapsed(drv->substream);
> >
> > try_to_freeze();
> >
> > }
> >
> > kfree(audio_frame);
> > audio_frame = NULL;
> >
> > return 0 ;
> >
> > }
> > [3 hwptr_app_ptr_buf_pos_analysis.xlsx <application/vnd.openxmlformats-officedocument.spreadsheetml.sheet (base64)>]
> >
--
Thanks and Regards
Chakravarthi Pradeep.K
Ph: 91 9980434900
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