Date: Thu, 30 Mar 2017 18:11:33 -0300 From: "Dr. Rolf Jansen" <rj@obsigna.com> To: freebsd-arm@FreeBSD.org Subject: Re: Enabling ADC on a Beaglebone Black running FreeBSD 12.0-CURRENT (BEAGLEBONE) Message-ID: <79EE9798-BCF0-4585-93F5-4E604142561F@obsigna.com> In-Reply-To: <20170330202858.GA22253@bluezbox.com> References: <0C4DCBB9-2642-4B0F-B15B-4139D5D8B249@obsigna.com> <271AFD8F-BD2C-445C-AB95-D7D07593E487@obsigna.com> <5D2FEB0D-64F3-488C-8458-85E7DF10EFB7@obsigna.com> <20170330202858.GA22253@bluezbox.com>
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Am 30.03.2017 um 17:28 schrieb Oleksandr Tymoshenko <gonzo@bluezbox.com>:
> Dr. Rolf Jansen (rj@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@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
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