Enabling ADC on a Beaglebone Black running FreeBSD 12.0-CURRENT (BEAGLEBONE)

[Dr. Rolf Jansen]

Am 30.03.2017 um 17:28 schrieb Oleksandr Tymoshenko <gonzo at bluezbox.com>:
> Dr. Rolf Jansen (rj at obsigna.com) wrote:
>> Today I updated once again my Beaglebone Black by
>> merging-in the latest FreeBSD 12.0-CURRENT (BEAGLEBONE)
>> snapshot, and once again I enabled the ADCs on the
>> Beaglebone in the device tree blob am335x-boneblack.dtb,
>> and the ADC is still working fine.
>> 
>> Even if it is not that a big hassle to modify the device
>> tree blob, I am curious on why the ADC has been disabled
>> in the blob in the first place, end even more, given the
>> fact that the device ti_adc driver is built-in to kernel
>> and once enabled, the ADC is functional.
>> 
>> Didn't it work at some time in the past? Now it is.
>> 
>> What is missing to activate the ADC in the device tree
>> blob by default?
> 
> Few months ago FreeBSD switched to using upstream DTB files
> instead of custom-made ones. For some reason ADC is disabled
> in upstream. If you're running recent FreeBSD you can use
> dtb overlays to enable ADC without hassle of maintaining
> custom dts file. You can do following:
> 
> 1. Create am335x-beaglebone-tscadc.dts with following
> content:
> 
> /dts-v1/;
> /plugin/;
> 
> / {
>    compatible = "ti,am335x-bone-green", "ti,am335x-bone-black", "ti,am335x-bone", "ti,am33xx";
> 
>    fragment at 0 {
>        target = <&tscadc>;
>        __overlay__ {
>            status = "okay";
>            adc {
>                ti,adc-channels = <0 1 2 3 4 5 6>;
>            };
>        };
>    };
> };
> 
> 2. Compile overlay:
>  $ dtc -I dts -O dtb -o am335x-beaglebone-tscadc.dtbo am335x-beaglebone-tscadc.dts
> 
> 3. Copy it to /boot/dtb/ directory on your BBB
> 
> 4. Enable overlay in /boot/loader.conf by adding following line:
> 
> fdt_overlays="am335x-beaglebone-tscadc.dtbo"


Oleksandr, thank you very much for drawing my attention to the dtb overlay facility.

I created and enabled the adc-dtb-overlay file as you explained above, and it works.

Best regards

Rolf