Re: Data source of record.bytes in audioctl

On 2023-07-04 12:00, Alexandre Ratchov wrote:
> On Mon, Jul 03, 2023 at 05:18:13PM -0400, Ricky Cintron wrote:
>> While troubleshooting some audio issues, I noticed that the values of
>> play.bytes and record.bytes in audioctl's output were identical, even
>> when only playing audio.
>>
>> 1) Is this expected behavior?
>
> yes, by default the device always does DMA in both directions
> (synchronously), so record.bytes increases like play.bytes
>
Great to know! This, along with the other details you've provided, will
help me understand what I'm seeing much more clearly now.

Thank you.

>> 2) What is the source of this data (record.bytes)?
>>
>
> The source is the audio hardware interrupts. The audio(4) driver
> handles them and increments its couter. The counter is readable by
> userland with the AUDIO_GETPOS ioctl.
>
>> I found it interesting that the values were the same, so I took a look
>> at mixerctl, and noticed that 'line' (which is an output) and 'mix'
>> (which has line as its only source) were the sources for both
>> record.adc variables. At that point I figured that simply removing
>> all sources from those two variables would eliminate all audio data
>> from those recording channels, but record.bytes continued to match
>> play.bytes. I even attempted to mute both ADCs and to disable
>> recording
>> in mixerctl (without rebooting), but nothing changed.
>>
>> I'm probably going to remove 'line' and 'mix' as sources for the ADCs
>> because they don't make sense there, but I'm still hoping to
>> understand
>> what's going on.
>>
>
> The mixer is a completely different thing and is completely
> independent from DMA. It is supposed to control the analog
> knobs/selectors, jack sensors, and alike.
>
> Setting the record level to 0 (or removing all sources) would make the
> ADC sample silence and produce zeros without affecting how it
> works. That's why record.bytes still increases.
>
>> # mixerctl -v
>> inputs.dac-2:3=126,126
>> inputs.dac-0:1=126,126
>> record.adc-0:1_mute=off [ off on ]
>> record.adc-0:1=124,124
>> record.adc-2:3_mute=off [ off on ]
>> record.adc-2:3=124,124
>> inputs.mix_source=line { line }
>> inputs.mix_line=120,120
>> inputs.mix2_source=dac-2:3 { dac-2:3 mix }
>> inputs.mix3_source=dac-0:1 { dac-0:1 mix }
>> outputs.spkr_source=mix2 [ mix2 ]
>> outputs.spkr_mute=on [ off on ]
>> outputs.spkr_eapd=on [ off on ]
>> outputs.line_source=mix3 [ mix2 mix3 ]
>> outputs.line_mute=off [ off on ]
>> inputs.line=85,85
>> outputs.line_dir=output [ none output input input-vr0 input-vr50
>> input-vr80
>> input-vr100 ]
>> outputs.line_boost=off [ off on ]
>> outputs.line_eapd=on [ off on ]
>> outputs.hp_source=mix2 [ mix2 mix3 ]
>> outputs.hp_mute=off [ off on ]
>> outputs.hp_boost=off [ off on ]
>> outputs.hp_eapd=on [ off on ]
>> record.adc-2:3_source=line,mix { line mix }
>> record.adc-0:1_source=line,mix { line mix }
>> outputs.line_sense=plugged [ unplugged plugged ]
>> outputs.hp_sense=unplugged [ unplugged plugged ]
>> outputs.spkr_muters=line,hp { line hp }
>> outputs.master=126,126
>> outputs.master.mute=off [ off on ]
>> outputs.master.slaves=dac-2:3,dac-0:1,spkr,line,hp { dac-2:3 dac-0:1
>> spkr
>> line hp }
>> record.volume=124,124
>> record.volume.mute=off [ off on ]
>> record.volume.slaves=adc-0:1,adc-2:3 { adc-0:1 adc-2:3 line }
>> record.enable=sysctl [ off on sysctl ]
>>
>>