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mtgrosser / bananapi-m2-berry-can

Using the CAN bus on Banana Pi M2 Berry
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CAN bus on Banana Pi M2 Berry

This repo includes some infos on making the CAN bus work on BPI M2 Berry.

Overview

The BPI M2 Berry is based on the Allwinner V40 chip, which includes a CAN controller. Unfortunately, the CAN pins are not exposed on the PCB, but used for connecting LEDs and Ethernet instead.

In order to make the CAN bus work on BPI M2B, the following steps are required:

Hardware modification

The Allwinner V40 pinctl allows routing CAN pins to either PA16/PA17 or PH20/PH21. By default, PA16/17 are used for ethernet, and PH20/21 for adressing the red and green LED.

Schematic for pins PH20 and PH21

In order to use PH20/21 for CAN, the driver transistors Q4 and Q5 need to be removed, as well as resistors R97, R101 and R110.

PCB before modification

R101 and R110 need to be replaced by solder bridges or 0402 zero-ohm links.

Components removed

The CPU CAN pins can then be accessed through the transistor base pads:

Blue square CAN_TX (PH20): Q4

Green square CAN_RX (PH21): Q5

Note: The black wire was connected for measuring purposes only, and is not required.

CAN pins exposed

Kernel patching

As of kernel version 5.17, no patching is required.

Kernels < 5.17 don't support CAN operation with BPI-M2B due to an incompatibilty in the sun4i_can kernel module. Therefore, the patch needs to be backported and the module needs to be rebuilt manually.

cp -rv /usr/src/linux-source-5.10.60-sunxi kernel-source
cd kernel-source
patch -p1 < sun4i_can.patch
cp /boot/config-5.10.60-sunxi .config
cp /usr/src/linux-headers-5.10.60-sunxi/Module.symvers .
make oldconfig
make scripts prepare modules_prepare
make -C . M=drivers/net/can
sudo cp drivers/net/can/sun4i_can.ko /lib/modules/5.10.60-sunxi/kernel/net/can/

Device tree overlay

The provided overlay disables the LEDs and enables CAN on pins PH20 and PH21 instead.

armbian-add-overlay bananapi-m2-berry-can.dts