Re: Reading ADC that comes from a multiplexer

[Fabio Estevam <festevam@gmail.com>]

Hi Peter,

On Wed, Sep 22, 2021 at 11:28 AM Peter Rosin <peda@axentia.se> wrote:

> Nice!
>
> While I don't completely understand that iio-device node in the beaglebone
> dts that didn't work for you, it looks like it's just a renumbering thing?

The beaglebone dts uses some undocumented properties such as:
iio-channels and iio-channel-names.

> However, your version only remapped 4 channels, and in that case your new
> iio-device only had those, i.e. 0-3. But the iio-mux was looking for the
> missing channel 4. Maybe that was why that variant didn't work?

Yes, this is where I got confused.

The stmpe811 has 8 channels. On the apalis board, the first four channels
(0 to 3) are used for touchscreen. The other 4 channels are for general purpose.

The ADC that is connected to the MUX is channel 4 (which is the first
one that is
free for general usage), so I had to pass:

io-channels = <&adc0 0>;

in the mux, instead of  io-channels = <&adc0 4> that I was originally trying.

and now the mapping is correct and I can read proper voltages when I
switch the mux.

Thanks!