Device Tree Blob for Beaglebone Black?

[Christian Mauderer]

On 24/02/2020 07:01, Chris Johns wrote:
> 
> 
>> On 24 Feb 2020, at 5:32 am, Christian Mauderer <list at c-mauderer.de> wrote:
>>
>> On 23/02/2020 17:07, Alan Cudmore wrote:
>>> I have been trying to bring up RTEMS with rtems-libbsd on the
>>> beaglebone black (latest master).
>>>
>>> I can run the regular RTEMS samples on the board, and a couple of the
>>> rtems-libbsd testsuite examples run as well.
>>>
>>> The samples such as ping01 and usb01 get a fatal exception in the
>>> function fdt_ro_probe_ , leading me to believe that maybe I am not
>>> using the correct device tree blob.
>>>
>>> I'm using the instructions here:
>>> https://git.rtems.org/rtems-docs/tree/user/bsps/arm/beagle.rst
>>>
>>> And I have am loading am335x-boneblack.dtb that I copied from a linux
>>> u-boot build. The instructions talk about getting the one from the
>>> FreeBSD repository, but there are many other files included in that
>>> dts source.
>>>
>>> What dtb is normally used for the Beaglebone black RTEMS libbsd testing?
>>>
>>> Is the dtb needed for the non-libbsd BSP?
>>>
>>> Also, is the ethernet supported on the RTEMS beagle BSP, or do I need
>>> libbsd to get ethernet?
>>>
>>> Thanks,
>>> Alan
>>
>> Hello Alan,
>>
>> I recommend to use the FreeBSD device trees. libbsd is FreeBSD based and
>> therefore works best with them. Normally I would suggest to use the
>> version matching the FreeBSD commit used in libbsd. But unfortunately in
>> the last commit that doesn't seem to work. Vijay had some problems with
>> it and noted that the version from FreeBSD commit
>> 19a6ceb89dbacf74697d493e48c388767126d418 works fine.
> 
> Is this with 5 branch in Libbsd?
> 
> I am a little confused about the branch to package in a release and also which FDT files we need for which branch. If different I feel a release will makes things more complicated. This flies into the BSP  vertical stack building in the RSB. 
> 
> I am working on releasing and I hope this does not block things. 
> 
> Chris

Hello Chris,

the non-working device tree is for the master branch from a few weeks
back. I didn't tested it with the 5-freebsd-12 branch.

Again: In the normal case I would just suggest to use the FDT sources
that match the FreeBSD commit we use for libbsd. That worked best for me
in the past. But in the current referenced commit FreeBSD has updated
the device tree sources to the ones from a recent Linux version and the
drivers haven't been adapted yet (on master - I expect that it works
better on 5-freebsd-12).

Regarding the release: I don't think you pack the FDT files (yet), do
you? So I don't see why there should be a reason for this topic to block
the release.

Note that the exact FDT version used for different BSPs is still a
bigger problem. Some BSPs expect a version provided by a board
manufacturer. Some use a random Linux DTB. And some work well with the
ones from FreeBSD (which is just a snapshot of the Linux ones) - that's
the method I prefer because it works well with libbsd most of the time.
I think currently the right device tree for the board is only documented
in the User Manual (if it is documented).

Best regards

Christian
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