Re: question on devicetree (nrf52840dongle)


Bolivar, Marti
 

Hi again Kristoff,

"Kristoff Bonne via lists.zephyrproject.org"
<kristoff=skypro.be@lists.zephyrproject.org> writes:

Hi all,


First, thanks to who reply off-list. :-)



I found the solution, so I will Just a reply for sake of the the
mail-achive:
In contrast to the device-tree module on linux/*BSD, the devicetree
source-files (i.e. the .dts file) are recompiled every time, so there is
no need to first convert the .dts source-files in binary blobs.
Just to be clear although I mentioned this in my response to your other
thread, they are not recompiled 'every time'. DTS files are processed
only when the configuration phase runs.

Since you mention blobs here, I will say that Zephyr converts DTS to the
generated header directly, and blobs never enter the picture.

The details are in the 'Input and output files' section of the
'Introduction to devicetree' page in the Zephyr docs:

https://docs.zephyrproject.org/latest/guides/dts/intro.html#input-and-output-files

In my case, as I just a hobbyist, I just modified the
"nrf52840dongle_nrf52840.dts" file and that solved my issue. (Alhough I
guess I would have needed to use an device-tree overlay file to do this
the "proper" way).



But I am still a bit puzzled by this.
The way I have done it now, I have made a modification that will impact
all my projects.
The device-tree files are in the 'boards' directory which is common to
all projects.

So, say you have two different projects with different pinmux settings,
how do you do this?
Create two different 'boards' , and compile the two projects with a
different '-b' setting?
As you yourself guessed, the right way is to use devicetree overlays in
the project directories.

Please see the relevant items in the 'Devicetree HOWTOs' page in the
documentation's devicetree guide for more details on overlays in Zephyr.

https://docs.zephyrproject.org/latest/guides/dts/howtos.html

Hope this helps,
Martí




Kristoff


On 24.05.21 15:40, Kristoff Bonne wrote:
Hi all,


I have been experimenting with running zephyr on some nrf52840dongle
device that I bought some time ago.


According the document on this device, zephyr should support both i2c
and spi on these devices, and as the nrf52840 a pinmux it should be
possible to use any pin for this.
Looking at the devicetree file (*) it says that i2c uses pins 26 and
27 for i2c0, and 30 and 31 for i2c1, which is a bit strange as of
these 4 pins, the dongle only exposes ports 26 and 30. (No idea why
the person who created this dts-file chose those pins).



Question:

- How exactly does the devicetree on zephyr work?
Can I assume that if I would modify the dts file compile it and 'link'
that dto-file in the compilation address, I would be able to use other
pins?

- Am I correct to assume that the device-tree file actually instructs
some part of the boot-process to configure the pinmux in a certain
way? (so it's not just a reflection of the configuration of the pinmux
'as it', but it a configuration that is pushed to the pinmux)

- Where can I find information on how to actually do this?




(*) boards/arm/nrf52840dongle_nrf52840/nrf52840dongle_nrf52840.dts


Thanks in advance for any help!


Kr.






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