Re: Meta-raspberrypi - how to configure device tree for MCP251x

Chris Tapp

Hi Khem,

There is nothing in /boot once the system has started, but if I mount /dev/mmcblk0p1 I can see a config.txt that includes:


This is what I could expect.

On a quick scan, this appears to be the same as the one in tmp/deploy/images/raspberrypi4/bootfiles - the timestamp for this file indicated it was old, so I had manually cleaned and rebuilt rpi-bootfiles for changes to RPI_EXTRA_CONFIG to propagate.

However, if I bring the CAN interface up:

ip link set can1 up type can bitrate 100000

and look in /proc/interrupts, I see:

 66:          0          0          0          0  pinctrl-bcm2835  25 Level     spi0.0

even though can1 is on spi0.1.


On 4 Oct 2021, at 17:49, Khem Raj <raj.khem@...> wrote:

can you check boot/config.txt and see fi your changes are there in your target ?

On Mon, Oct 4, 2021 at 1:21 AM Chris Tapp <opensource@...> wrote:

Sorry, I meant to add that I have tried adding the following to local.conf:

   dtparam=spi=on \n \
   dtoverlay=mcp2515-can0,oscillator=16000000,interrupt=25 \n \
   dtoverlay=mcp2515-can1,oscillator=16000000,interrupt=23 \n \

However, this did not make any difference to the interrupts.

Since then, I have manually changed mcp2515-can1-overlay.dts in the kernel build tree (after running bitbake - c do_configure virtual/kernel) and rebuilt the kernel / image. This does result in the interrupt mapping changing, and both CAN channels then operate correctly.

Does anyone know why RPI_EXTRA_CONFIG doesn’t appear to be taking effect?


Chris Tapp

You can tell you're getting older when your car insurance gets real cheap!

On 1 Oct 2021, at 22:38, Chris Tapp <opensource@...> wrote:

I am having trouble getting the Waveshare 2-CH CAN HAT working with an RPI4. Channel 0 does not come up, channel 1 does, but it will only send one message (eventually reporting "write: No buffer space available”) and not receive anything.

Looking at the mcp2515-can0-overlay.dts and mcp2515-can1-overlay.dts device tree files in /tmp/work-shared/raspberrypi4/kernel-source/arch/arm/boot/dts/overlays/, it looks as if the interrupts are not mapped as required for the board.

     DTS               HAT
CAN0  brcm,pins = <25>  PIN23
CAN1  brcm,pins = <25>  PIN25

This doesn’t look right, and seems consistent with the behaviour I am seeing.

I would also like to check the device chip select signals, but I can't see how (if) they are mapped in the dts files.

How can I override these settings when I build the image?


Chris Tapp

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