[EXTERNAL] Re: BeagleBone Black Networking (wifi and/or wired)

[Chris Johns]

On 8/6/19 5:58 pm, Christian Mauderer wrote:
> ----- Ursprüngliche Mail -----
>> Von: "Oyake, Amalaye (386M)" <amalaye.oyake at jpl.nasa.gov>
>> An: "Chris Johns" <chrisj at rtems.org>, "Vijay Kumar Banerjee" <vijaykumar9597 at gmail.com>, "Christian Mauderer"
>> <christian.mauderer at embedded-brains.de>
>> CC: "RTEMS Users" <users at rtems.org>
>> Gesendet: Samstag, 8. Juni 2019 04:57:02
>> Betreff: Re: [EXTERNAL] Re: BeagleBone Black Networking (wifi and/or wired)
> 
>> Device Tree overays are a method used to update the Device Tree. Given a device
>> tree that describes all the devices, let's say you add a new SPI device, you
>> can update the device tree with a (blob) device tree overlay.
>>
>> I should ask (without Googling), What is the Device Tree Overlay mechanism in
>> RTEMS?
> 
> 
> Hello Amalaye,
> 
> as far as I know, the device tree overlay mechanism in RTEMS is not implemented. There is the prototype of fdt_overlay_apply() in libfdt.h but there is no implementation. So there are two methods:
> 
> 1. Applying the overlay on a build machine. Vijay did that during his tests.

How do you do this?

> 2. Use the U-Boot mechanism to apply overlays before booting RTEMS. That should most likely work too. But I didn't test it yet.

OK

>> On 6/7/19, 6:17 PM, "users on behalf of Chris Johns" <users-bounces at rtems.org on
>> behalf of chrisj at rtems.org> wrote:
>>
>>    On 8/6/19 1:53 am, Vijay Kumar Banerjee wrote:
>>    > 
>>    > I would like to add that in two projects of this year( I2C and PRU-ICSS drivers)
>>    > we
>>    > are using our own device tree overlays that make our drivers work. Where to add
>>    > the device
>>    > tree related stuff seems like an important question.
>>    
>>    What are device tree overlays?
> 
> Like Oyake already said: They are some small pices of device trees that are just added to the base tree in it's binary form. Linux (and most likely FreeBSD too) supports that even after boot. If you add an overlay it re-parses the device tree, updates GPIO settings and loads new drivers. The alternative is to let the boot loader apply them during boot.

What is needed to do this? Maybe I can add it to rtems-boot-image as a way to
handle this at the u-boot version.

> A practical example would be adding a I2C device like a DS1338 RTC to the extension connector of the Beagle: https://github.com/beagleboard/bb.org-overlays/blob/master/src/arm/BB-I2C2-RTC-DS1338.dts

I see the need for this.

> I suggested them for Vijays GSoC project to be able to add an I2C adaption layer so that libbsd uses the RTEMS i2c drivers. That's necessary so that RTEMS applications can still use the RTEMS i2c interface but at the same time the FreeBSD drivers (in that case for some chip related to HDMI) can use the BSD interface.

OK.

Chris