missig spidev2.1

mafishmafish New Member Posts: 4

I work on a project where I need to communicate with two external MCUs, via SPI.
I've successfully used MRAA lib to test the communications to single MCU, but when I've tried to write to the second one I've noticed I only got /dev/spidev2.0 in my system.
As I understand to access the second MCU (using same MOSI/MISO/SCK lines) I should have spidev2.1 also present.
What might be an issue and how to fix it?

I am using ubilinux kernel with RT patch right now,
Linux ubilinux4 4.9.45-rt37-upboard+ #1 SMP PREEMPT RT Sun Aug 11 10:20:11 UTC 2019 x86_64 GNU/Linux
although my issue was also present before patching.


  • Dan O'DonovanDan O'Donovan Administrator, Moderator, Emutex Posts: 232 admin

    Hi @mafish

    You could try adding the following parameter on the kernel command line:

    To extend the kernel command line parameters, one option is to edit /etc/default/grub and add the parameter to the $GRUB_CMDLINE_LINUX_DEFAULT variable, and then run sudo update-grub2, and reboot.

    I hope that helps.

    Best regards,

  • mafishmafish New Member Posts: 4
    edited August 12

    Thank you, for a quick and clear response!
    It's a partial success. The device spidev2.1 has appeared in /dev/ and MRAA library is initializing the interface nominally, but there is no output on CS1 pin (it is constantly in high state), all the other pins(MOSI/MISO/SCK) work fine.
    Can CS1 pin be somehow rewired to other GPIO? Or maybe I need to somehow show the kernel what GPIO to use as CS1?

    [EDIT]: I've just checked the bios. in Advanced/HAT Configuration/GPIO Configuration in Pin Order, pins from SPI (Pin 19, 21, 23 and 24 -> 24 being CS0) are grayed out and marked as 'SPI2' and pin 26 (CS1) is represented as regular GPIO ( can be set either Input or Output), is this BIOS related error then? I haven't upgraded my BIOS, it is completely stock.

  • Dan O'DonovanDan O'Donovan Administrator, Moderator, Emutex Posts: 232 admin

    The UP board doesn't have a real CS1 signal for the SPI2 bus, so we used a GPIO pin instead for that... or so I thought... but I've just discovered that the patches I created initially for the v4.4 kernel to make that work were dropped from later UP board kernels. I'm not sure why. :(

    I don't think these will apply cleanly on the v4.9 kernel, but perhaps you might like to see if you can integrate them manually?

  • mafishmafish New Member Posts: 4
    edited August 14

    For now, I have no idea how to make use of the links you posted. I guess its time to learn something new.
    I will update the topic once I've find and implement a solution of some sort. Thank you nonetheless.
    [EDIT]: can you recommend any source of knowledge in this topic (kernel patches, device drivers etc), other than raw documentation? Any online(and free) courses or tutorials.

  • rushurushu New Member Posts: 3

    :/ I have the same problem when I need to use the spidev 2.1 in UP board. Is it need to use UP square instead?

  • mafishmafish New Member Posts: 4

    Hi @rushu , I've figured out it can be done using software and GPIO toggling, with some reasonable latency. Using MRAA C++ library and Ubilinux with PREEMPT-RT patch I have achieved ~70us delay in CS1 switching, compared to regular hardware CS0. It's good enough for me.

  • rushurushu New Member Posts: 3

    Thanks @mafish , you are really good! It seems a good way to solve the problem.
    But I am using Ubuntu and python, I still don't know how to patch preempt RT under Ubuntu system.
    May be I should tend to use the Ubilinux.

  • DCleriDCleri Administrator, AAEON Posts: 731 admin


    Ubilinux is no longer supported and it won't receive future updates.

    Thanks to your feedback we will include a patch in a future kernel to re-enable the CS on recent kernel also for Ubuntu.

    About the Preempt-rt patches we will review internally if release it as a separate kernel or include in the standard one.

  • rushurushu New Member Posts: 3

    Great!We are looking forward to the official updates.

  • horsonhorson New Member Posts: 1

    Great!We are looking forward to the official updates.

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