Getting second SPI interface to work with nerves_system_rpi3

I’m working on an Elixir application that I’m deploying to a Raspberry Pi Model B using Nerves and nerves_system_rpi3.

I’m communicating with devices using Circuits.SPI and the standard /dev/spidev0.0 and /dev/spidev/0.1 channels. Now I’d like to talk to more devices, and use the second SPI interface to do so (info about SPI devices).

To do this, I am led to believe that I need to add the following line to /boot/config.txt:


I have therefore followed the instructions for overwriting files in the boot partition. I copied fwup.conf and config.txt to my '/configdirectory and edited them andconfig.exs` to point to one another.

However, when I deploy to my RPi, the devices do not show up:

iex> Toolshed.cmd "ls /dev/spi*"

I was hoping for a /dev/spidev1.0! My change is definitely there:

iex> Toolshed.cmd "grep spi /boot/config.txt"

Help! How do I troubleshoot this? is there something I’m missing? I would appreciate any pointers I can get!

Hi @tobin

If you add dtdebug=on to config.txt the early boot that happens in the VideoCore 4 GPU will be logged.
To see the log after Linux is booted, use vcdbg log msg.

Also see this “freshman” question thread in this forum.

(caveat, I’ve not (yet) used any SPI devices)

I just now tried this on my Rpi3B+ with latest Nerves etc. and got the log ::
Failed to load overlay 'spi1-3cs'
brfs: File read: /mfs/sd/overlays/spi1-3cs.dtb
and sure enough, /boot/overlays does not contain any spi1*.dt?
Drop the right .dtbo in there and things might work :slight_smile:

To "drop the right .dtbo . . " you need to edit fwup.conf to make sure the spi1-3cs.dtbo file is copied in all the correct places.


Fantastic! Thank you so much for that great answer.

I downloaded spi1-3cs.dtbo from the raspberrypi/firmware github and then added these lines to my fwup.conf:

file-resource spi1-3cs.dtbo {                                                                                                                 
    host-path = "${NERVES_APP}/config/spi1-3cs.dtbo"                                                                                          
on-resource spi1-3cs.dtbo { fat_write(${BOOT_B_PART_OFFSET}, "overlays/spi1-3cs.dtbo") }  

… a quick mix firmware, and I’ve now got three more SPI channels to play with!


Addendum: There are a couple more lines of on-resource spi1-3cs.dtbo {...} I needed to add to my fwup.conf (I just copied what was there). Notably I had the BOOT_B_PART_OFFSET line but not the corresponding A line, which meant it only worked once every two times I deployed the firmware!

@tobin, Hey, good work !
Think you didn’t need to fetch that spi1-3cs.dtbo file . . that and many other overlays are already present in the nerves_system_rpi3 artifacts cached in your ~/.nerves folder.
Just change that file resource path to be like existing ones above coming from images/rpi-firmware/overlays/