On Dec 13, 2018, at 9:00 PM, Brian Badger <brian@...> wrote:That’s exactly how it works. The TLV320AIC3204 has three inputs that can be connected to the ADC. Each input also has an inline resistor that you can select from the mixer. We suggest that you use 10k, because that’s been shown to work in all the situations we’ve tried, but if you need to do some advanced configuration you can use the 20k and 40k values. Please also note that it is a valid configuration for the codec to hook both input 1 and 2 to the ADC at the same time. The signals will merely get mixed. So, if that’s not something you desire, remember to turn off 1 when 2 is in use and vice-versa.
Also read the entire mixer description. There are indeed switches for things like “IN1L to Right Mixer” where you can cross things up.
The “ADC Level” analog control determines the input gain for these. Left and right are separately controllable.
I’d love to be able to pare down these options to be more specific to udrc/draws, but the alsa code doesn’t really allow you to do that very easily.
On the output side, it’s quite a bit simpler. There’s one right and one left output off of the DAC. They are hooked to one of two amplifiers, LO and HP. LO is line out, and HP is headphones. UDRC/Draws only brings out the LO amplifier to pins. There’s an “LO DAC” control that should always be on unless you never intend on transmitting. This hooks the output of the DAC to the LO amplifier. There are then two output controls, one for each of the left and right pin. These are brought out to the output pin on the DIN6.
The trickiness here is that there are two level controls for the output. The first is the PCM control. This controls output from the DAC itself. The thing to note about this control is that it’s a digital control, which means it’s really just multiplying input values to the DAC by a scaling factor. That means that the lower you set it, the less effective bits of the DAC you’re using. This can cause more quantization noise in your output. The other control is the “LO Drive” control. This controls the gain of the LO amplifier. Because of the lack of quantization issues, you would prefer to use this one for the bulk of your setting if possible.
With regards to the “LO Drive” and “PCM” controls, my experience has shown that 0dB on both controls is pretty close to clipping the outputs, so use caution when adjusting them above 0dB.
If you need more output than the defaults can provide, there’s a secret device tree overlay called udrc-boost-output that’s in our repository that you can use to change the power source of the LO amplifier. How to use such is an exercise for the reader since it’s rarely needed.
And what is IN3? AUnused.
Annaliese McDermond (NH6Z)