[Openvortex-dev] au88x0 PCM Volume control

[Raymond]

The proposed PCM Volume controls of the playback device 0 of au88x0 
driver allow any ALSA application using the PCM Volume control 
(.iface=SNDRV_CTL_ELEM_IFACE_PCM) associated to the sudevice to change 
the volume (-48dB to 6dB) when the audio passing through the hardware 
mixer of au88x0.


Mono
                            0dB
DMA -> FIFO -> SRC -> MIXIN ---> MIXOUT -> Equalizer -> Front Left
                        |   0dB
                        +------> MIXOUT -> Equalizer -> Front Right
                        |   6dB
                        +------> MIXOUT --------------> Rear Left
                        |   6dB
                        +------> MIXOUT --------------> Rear Right

Stereo

                            0dB
DMA -> FIFO -> SRC -> MIXIN ---> MIXOUT -> Equalizer -> Front Left
            |           |   6dB
            |           +------> MIXOUT --------------> Rear Left
            |               0dB
            +> SRC -> MIXIN ---> MIXOUT -> Equalizer -> Front Right
                        |   6dB
                        +------> MIXOUT --------------> Rear Right

Surround40

                            0dB
DMA -> FIFO -> SRC -> MIXIN ---> MIXOUT -> Equalizer -> Front Left
            |               0dB
            +> SRC -> MIXIN ---> MIXOUT -> Equalizer -> Front Right
            |               6dB
            +> SRC -> MIXIN ---> MIXOUT --------------> Rear Left
            |               6dB
            +> SRC -> MIXIN ---> MIXOUT --------------> Rear Right

> Description of the patch (beta)
> - add PCM Volume control by using the hardware mixer of au88x0
>
>
> TEST AT YOUR OWN RISK !!!
>
> The audio will be distorted when total gain exceed the limit of 18-bits
> DAC in AC97 codec.
>
>
> Any comment/suggestion or programs to test the feature are welcome.
>
>
> > Hi,
>
>
> > On Mon, 2005-08-29 at 10:28 +0800, Raymond wrote:

> > > Distortion occur when the combined gain of audio data, hardware
> > > mixer ,  equalizer and 3D effect > 6dB ( limit by the 18-bits DAC i
> > > n AC97 codec)
>
>
> > The maximum gain possible for a entire audio pipe should obvisouly not
> > exceeded.

Why the hardware mixer in the current ALSA driver is set to zero gain in 
vortex_adb_allocroute() when capturing audio from 18-bits ADC to 16-bits 
audio ? ( In theory, it should be -6dB )


                                              AC97
16bits Audio                 0dB        18bits   Analog
DMA <- FIFO <- SRC <- MIXOUT <- MIXIN <- ADC  <- MIXER <---- MIC
                                       |           |
DMA <- FIFO <- SRC <- MIXOUT <- MIXIN <+           +---------LINE IN
                                                   |
                                                   +---------VIDEO
                                                   |
                                                   +---------CD
                                                   |
                                                   +---------AUX
                                                   |
                                                   +---------PHONE
                                                   |
                                                   +---------MIX


> > > In the ALSA au88x0 driver, the hardware mixer provide default gain
> > > of  6dB ( 16-bits auido data to 18-bits DAC in AC97 codec ) for the
> > > left/right channels of au8820 and the rear channels of au8810/au8830
> > > (to  SDAC of quad codec),
> >  >
> > > For the front channels of au8810/au8830, zero gain in hardware mixer
> > > and  this 6dB gain is most likely controlled by the equalizer or 3D
> > > effect.
> > >
>
> > I would suggest using the correct signed or unsigned type instead of
> > doing explicit type conversions.


static void
vortex_mix_setinputvolumebyte(vortex_t * vortex, unsigned char mix,
                              int mixin, unsigned char vol)
{
        int temp;

        hwwrite(vortex->mmio,
                VORTEX_MIX_INVOL_A + (((mix << 5) + mixin) << 2), vol);
        if (1) {                /* this_10, initialized to 1. */
                temp =
                    hwread(vortex->mmio,
                           VORTEX_MIX_INVOL_B + (((mix << 5) + mixin) << 2));
                if ((temp != 0x80) || (vol == 0x80))
                        return;
        }
        hwwrite(vortex->mmio,
                VORTEX_MIX_INVOL_B + (((mix << 5) + mixin) << 2), vol);
}


static int snd_vortex_adb_pcm_change_vol(vortex_t *vortex,int mixin,int
mix,int volume)
{
        if ( volume >= 128 )
                vortex_mix_setinputvolumebyte(vortex, mix, mixin, volume-128);
  // GAIN
        else
                if ( volume < 64 )
                        vortex_mix_setinputvolumebyte(vortex, mix, mixin, 
0x80);        // MUTE
                else
                        vortex_mix_setinputvolumebyte(vortex, mix, mixin, 
volume+128);  // ATTEN
        return 0;
}