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

[Chris Johns]

On 9/6/19 4:29 pm, Vijay Kumar Banerjee wrote:
> On Sun, Jun 9, 2019 at 6:22 AM Chris Johns <chrisj at rtems.org
> <mailto:chrisj at rtems.org>> wrote:
>     On 8/6/19 5:58 pm, Christian Mauderer wrote:
>     > ----- Ursprüngliche Mail -----
>     >> Von: "Oyake, Amalaye (386M)" <amalaye.oyake at jpl.nasa.gov
>     <mailto:amalaye.oyake at jpl.nasa.gov>>
>     >> An: "Chris Johns" <chrisj at rtems.org <mailto:chrisj at rtems.org>>, "Vijay
>     Kumar Banerjee" <vijaykumar9597 at gmail.com
>     <mailto:vijaykumar9597 at gmail.com>>, "Christian Mauderer"
>     >> <christian.mauderer at embedded-brains.de
>     <mailto:christian.mauderer at embedded-brains.de>>
>     >> CC: "RTEMS Users" <users at rtems.org <mailto: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?
> 
> I used `fdtoverlay` from libfdt on linux host. 

Could cpukit/dtc/libfd in RTEMS be updated to support this code? I see freebsd's
kernel has the code.

> 
>     > 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 <mailto:users-bounces at rtems.org> on
>     >> behalf of chrisj at rtems.org <mailto: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.
> 
> I have also tried to automate it by adding it in uEnv.txt as a script, it worked
> nicely to apply
> the overlay on the blob, I haven't tested it with any app though, but the
> overlay applied
> successfully. Here's what the test uEnv.txt looks like. 
> ```
> setenv bootdelay 5
> uenvcmd=run overlay_cmd boot
> overlay_cmd=fatload mmc 0 0x80800000 rtems-app.img; fatload mmc 0 0x88000000
> am335x-boneblack.dtb; fatload mmc 0 0x88100000 am335x-rtems.dtbo; fdt addr
> 0x88000000; fdt resize 0x1000; fdt apply 0x88100000;
> boot=bootm 0x80800000 - 0x88000000;
> ```
> 
> You can add something like this to the uEnv.txt in SD card image. In the above
> script
> the am335x-boneblack.dtb is the one from linux and am335x-rtems.dtbo is generated
> with dtc from the overlay written by me.

Ah I see. I think this could be added to rtems-boot-image. There is something
attractive about building the fdt at run time on the board from the needed pieces.

Chris