[alsa-devel] ASoC: DAPM and differential inputs

[Jeremy McDermond]

I’ve been working on the tlv320aic32x4 driver for a while now to add some features for some projects I’m working on using the chip.  I’m trying to wrap my head around DAPM and getting it to work with the variety of inputs on the aic32x4.

Basically, the codec has a set of registers that control the positive and negative inputs to each of the right and left input mixers.  The only setting is what value of resistor to connect between the input pin and a particular mixer (none, 10k, 20k, 40k).  For example, you can have a differential pair between IN1_R and IN2_R, or between IN1_R and IN3_R, or single ended by setting the negative pin to the common.  So, there’s a lot of flexibility and not just a differential “mode”.  The registers would even allow you to set up two negative pins, although I’m not sure why that would be useful.

I’m currently setting up DAPM so that both the positive and negative pins are wired to a single mixer.  This doesn’t seem to be working since only the negative pin seems to cause the path to be enabled.  Do I have to set up another “Negative Right” and “Negative Left” mixer to handle the negative pins?  Am I missing something else?

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Jeremy McDermond (NH6Z)
Xenotropic Systems
mcdermj at xenotropic.com