Cape4all Alsa Control Registers - HoerTech-gGmbH/Cape4all GitHub Wiki

The following table contains a list which control registers of the ADAU1761 codec can be set with which alsa controls.

Alsa has 2 names for each control, a simple mixer control name (alsa simple) and a card control name (alsa control).

alsamixer shows the simple mixer control names. amixer can use both. The alsa control names are specified by the driver as such. The simple names are derived from the control names by leaving out recognized parts of the name.

The names given in the following table need to be prepended by "C0 ", "C1 ", "C2 " to choose which of the codecs should be influenced.

Some alsa controls control both a left and a right channel.

amixer set "simple name" -- value

• value can be given as:
  • <INT>: directly give the value that is written into the codec's bits. Alsa will perform any necessary left shift, not you, see last section on this page.
  • <INT>%: Map the percentage to the range of possible hardware values
  • <FLOAT>dB: For volume controls, values can be given in dB
  • off, mute: mute or switch off
  • on: unmute or switch on
• When an amixer simple control controls 2 channels, then
  • giving a single value sets both channels to the same value
  • 2 different values can be given as two of the above values separated by comma: valueL,valueR
  • Only the left value can be set by giving valueL, (that's valueL-comma-nothing)
  • Only the right value can be set by giving the value as 0+,valueR (that's zero-plus-comma-valueR)

amixer cset name="control name" -- value

• value can only be given as
  • <INT>: directly give the value that is written into the codec's bits, as above. See last section on this page about not shifting left.
  • on
  • off or mute
• When an amixer card control controls 2 channels, then
  • giving a single value sets both channels to the same value
  • 2 different values can be given as two of the above values separated by comma: valueL,valueR
  • Only the left value can be set by giving valueL, (that's valueL-comma-nothing)
  • Only the right value can be set by giving the value as ,valueR (that's nothing-comma-valueR)

Using the simple alsa names is preferable when we want to set a value in dB. Using the control names is preferable when

• Two different alsa card control names are mapped to the same alsa simple name, so that one of these two controls cannot be set with alsa simple
• When only the right channel of a stereo control should be influenced and the 0+,valueR specification is too unreadable.

• Table cell for alsa simple name is empty: I have not bothered finding out the alsa simple name. You can add it when you find it out.
• Alsa simple name is "": Use alsa simple names C0, C1, or C2 without a space to use these.
• N/A* : The trailing asterisk means, the driver has a control for this, but does not activate it in the Cape4all configuration.
• When column C contains 2, then this is a stereo alsa control, and the alsa control controls 2 hardware registers. Find the register for the other side by searching for the other table row with the same alsa control name.
• DS Name: name of the control in the ADAU1761 data sheet.
• E: Endedness. Some controls as intended for differential microphones (D), some are intended for single-ended microphones (S). Replace "microphones" with other sound hardware as applicable.
• Mask: unimportant, do not let this value bother you. It is the bit mask that isolates this control from the full byte. Not needed for amixer operations.
• DAPM: Dynamic Audio Power Management

All examples affect codec C0. They can be adapted to affect C1 or C2.

# Bits 3-4 in 400b set LDBOOST, same bits in 400d set RDBOOST.  
# They allow 3 settings: mute, 0dB, 20dB. Set both to +20dB
amixer set "C0 PGA Boost" -- 20dB
# Set LDBOOST to 0dB and RDBOOST to mute
amixer set "C0 PGA Boost" -- 0dB,-999dB
# Leave LDBOOST unchanged, set RDBOOST to 20dB
amixer set "C0 PGA Boost" -- 0+,20dB
# Set both to mute
amixer set "C0 PGA Boost" -- 0,-999dB

# Bit 1 in 400e sets LDMUTE, in 400f sets RDMUTE.
# These are independent mute switches in differential paths.
# Set the left to mute, leave the right unchanged
amixer cset name="C0 Capture Switch" mute,
# Set both to mute
amixer cset name="C0 Capture Switch" mute

# Set only the right one to unmute
amixer cset name="C0 Capture Switch" ,on # use "on" instead of "unmute"
# or
amixer cset name="C0 Capture Switch" ,1

Suppose you want to set the RINPG value of codec C2 to -3dB using the INT value method. This is your workflow:

1. Find the description of RINPG in the data sheet https://www.analog.com/media/en/technical-documentation/data-sheets/ADAU1761.pdf. It is the "Gain for a right channel single-ended input from the RINP pin, input to Mixer 2". It is located in the 3 bits [6:4] of the register at 0x400C.
2. Find the necessary bit pattern that you need to set these bits to. The data sheet shows that -3dB corresponds to bit pattern: 100 (Set bit 6 to one, set bits 5 and 4 to zero).
3. Translate the bit pattern to an int. binary number "100" has value 4 (= 0*1 + 0*2 + 1*4).
   • If you were the driver you would need to left shift this value 4 by four bits, so that you are actually setting Bits 4-6 and not Bits 0-2. You would also take care not to alter the values of the other bits in the same byte.
   • But when using amixer, then you are not responsible for the left shift nor for caring about the other bits in the same byte. The alsa driver will take care of this for you.
   • Stick to the value 4 from the bit pattern "100". Do not alter your number. Do not shift bits.
4. Find out the alsa names for RINPG by searching the table above:
   • The simple name is "Input 3". The card control name is "Input 3 Capture Volume"
   • Notice that this is is not mapped as a stereo control, but as a single-channel control: Column C of our table contains a "1".
5. Set this value with amixer set or amixer cset:

amixer set "C2 Input 3" -- 4
amixer cset "C2 Input 3 Capture Volume" -- 4