sensors and bias

[Daniel Drake]

Hi,

On XO-1, we had an ALSA switch that enabled mic bias. This was used by
measure when being put into resistance sensor mode.

However, on XO-1.5, when Mitch Bradley suggested how to implement sensor
mode, his advice was "disable bias, enable the DC port and select it as
input"

Also, our DC input port does not seem to have any bias options.
http://dev.laptop.org/~dsd/20090713/codec0.txt
It is NID 0x1e.

The only nodes that have bias options are 0x1a and 0x1b (the analog
microphone inputs).


Not knowing much about this area, I'm confused. Is bias useful or not
when dealing with sensors? Have we excluded the possibility to control
it on XO-1.5?

(The current XO-1.5 kernel has a switch to control "DC Input Bias" but
this was an oversight, it doesn't do anything because NID 0x1e has no
bias settings.)

Daniel