Please see my second edit above.
Also, I'd say that the GPIO1 line on the audio codec serves solely to inform the codec of the headphones insertion. Why does the codec need that, I can't say because it isn't documented.
Edit: Thank you for pointing it out, now I see the daughterboard schematic. Let me check it out.
Edit #2: I could be wrong, but aren't the left and right audio channel switched at the daughterboard schematic? Shouldn't the tip be the left channel, and shouldn't the first ring be the right channel? To make matters worse, I've tried playing some left/right channel sample music, which can be heard as expected using the built-in speakers, but when the headphones are connected... I hear both channels in both earpieces, i.e., there's seems to be no separation between the channels.
Edit #3: I really don't seem to understand how the headphones detection, the jack part, actually works? When no headphones are connected, HP_DET_H seems to be connected to HPO_L through a single resistor, R16 (1K, the other couple of resistors are 0R or NC), while HP_DET_H is not pulled low by R234, because it's marked as NC.
Also, I'd say that the GPIO1 line on the audio codec serves solely to inform the codec of the headphones insertion. Why does the codec need that, I can't say because it isn't documented.
Edit: Thank you for pointing it out, now I see the daughterboard schematic. Let me check it out.
Edit #2: I could be wrong, but aren't the left and right audio channel switched at the daughterboard schematic? Shouldn't the tip be the left channel, and shouldn't the first ring be the right channel? To make matters worse, I've tried playing some left/right channel sample music, which can be heard as expected using the built-in speakers, but when the headphones are connected... I hear both channels in both earpieces, i.e., there's seems to be no separation between the channels.
Edit #3: I really don't seem to understand how the headphones detection, the jack part, actually works? When no headphones are connected, HP_DET_H seems to be connected to HPO_L through a single resistor, R16 (1K, the other couple of resistors are 0R or NC), while HP_DET_H is not pulled low by R234, because it's marked as NC.