On 2021-09-22 04:18, Fabio Estevam wrote:
> Hi Peter,
>
> I have a SN74LV4051 multiplexer that is controlled by 3 GPIOs and I
> described like this in DT:
>
> adcmux: mux-controller {
> compatible = "gpio-mux";
> #mux-control-cells = <0>;
> mux-gpios = <&gpio3 31 GPIO_ACTIVE_HIGH>,
> <&gpio3 30 GPIO_ACTIVE_HIGH>,
> <&gpio3 26 GPIO_ACTIVE_HIGH>;
> };
>
> adc-mux {
> compatible = "io-channel-mux";
> io-channels = <&adc 4>;
> io-channel-names = "parent";
> mux-controls = <&adcmux>;
> channels = "chan0", "chan1", "chan2", "chan3",
> "chan4", "chan5", "chan6", "chan7";
> };
>
> /sys/class/mux/muxchip0/ is created:
>
> # ls /sys/class/mux/muxchip0/
> device of_node power subsystem uevent
>
> Sorry for the trivial question, but I haven't found any examples.
>
> What is the userspace command if I want to expose "chan3" to be read
> by the ADC 4 channel?
Basically, the whole point is that you simply don't. The iio-mux exposes
the channels as 8 new ADCs, and whenever you read a value from one of
them, the iio-mux operates the gpios for you, giving you the impression
that you have 8 independet ADCs. They are of course not independent, but...
Anyway, I have almost the exact same setup in
arch/arm/boot/dts/at91-tse850-3.dts
mux: mux-controller {
compatible = "gpio-mux";
#mux-control-cells = <0>;
mux-gpios = <&pioA 0 GPIO_ACTIVE_HIGH>,
<&pioA 1 GPIO_ACTIVE_HIGH>,
<&pioA 2 GPIO_ACTIVE_HIGH>;
idle-state = <0>;
};
envelope-detector-mux {
compatible = "io-channel-mux";
io-channels = <&env_det 0>;
io-channel-names = "parent";
mux-controls = <&mux>;
channels = "", "",
"sync-1",
"in",
"out",
"sync-2",
"sys-reg",
"ana-reg";
};
(but with the added complication that my ADC is not an ordinary ADC, but
instead a DAC and a comparator, such that the envelope of an AC signal can
be detected by a series of measurements, and I only use 6 channels)
That's exposed to user-space as:
$ ls "/sys/bus/iio/devices/iio:device3"
in_altvoltage2_compare_interval in_altvoltage5_scale
in_altvoltage2_invert in_altvoltage6_compare_interval
in_altvoltage2_raw in_altvoltage6_invert
in_altvoltage2_scale in_altvoltage6_raw
in_altvoltage3_compare_interval in_altvoltage6_scale
in_altvoltage3_invert in_altvoltage7_compare_interval
in_altvoltage3_raw in_altvoltage7_invert
in_altvoltage3_scale in_altvoltage7_raw
in_altvoltage4_compare_interval in_altvoltage7_scale
in_altvoltage4_invert name
in_altvoltage4_raw of_node
in_altvoltage4_scale power
in_altvoltage5_compare_interval subsystem
in_altvoltage5_invert uevent
in_altvoltage5_raw
$ cat "/sys/bus/iio/devices/iio:device3/name"
envelope-detector-mux
But the above gets tedious fast, and iio:device3 can of course be something
else etc etc, which is why libiio is the recommended interface.
ctx = iio_create_local_context();
dev = iio_context_find_device(ctx, "envelope-detector-mux");
chn = iio_device_find_channel(dev, "altvoltage2", 0);
iio_channel_attr_read_longlong(chn, "raw", &value);
Hope that helps!
Cheers,
Peter
