Quick notes on the Nerves setup steps to enable an mcp2515 can controller on an rpi3

can0_setup.md

can0 setup

(for mcp2515 controller like the PiCAN2)

1. fork (or clone) nerves_system_rpi3 locally into the parent directory of your project

2. edit mix.exs and change the nerves_system_rpi3 lines to point to your local one:

    def system("rpi3"), do: [{:nerves_system_rpi3, path: "../nerves_system_rpi3", runtime: false}]
   

3. mix deps.get

4. mkdir config/rpi3 to set up a place to store some customized rpi configs

5. copy over fwup.conf and config.txt from your local nerves_system_rpi3 repo

    cp ../nerves_system_rpi3/fwup.conf config/rpi3/fwup.conf
   
    cp ../nerves_system_rpi3/config.txt config/rpi3/config.txt
   

6. in config/config.exs point nerves at new fwup.conf file:

   config :nerves, :firmware, fwup_conf: "config/rpi3/fwup.conf"

7. edit config/rpi3/fwup.conf to include the additional overlays needed, by default the mcp2515-can0 overlay is not included in the base image. inside fwup.conf notice how the the overlay is set up for w1-gpio-pullup and use that as a pattern for adding our new overlay. search for all the lines containing w1-gpio-pullup, this will get you oriented for how the overlay is defined and then copied to each partition. You will need to do the same for the mcp2515-can0 overlay. There are four lines to add.

   1. set up a new file resource definition (around line 117) by adding:

      file-resource mcp2515-can0.dtbo { host-path = "${NERVES_SYSTEM}/images/rpi-firmware/overlays/mcp2515-can0.dtbo" }

   2. write the overlay file inside the task complete block (add around line 212) with all the other on-resource lines:

      on-resource mcp2515-can0.dtbo { fat_write(${BOOT_A_PART_OFFSET}, "overlays/mcp2515-can0.dtbo") }

   3. do the same inside the task upgrade.a block (around line 268):

      on-resource mcp2515-can0.dtbo { fat_write(${BOOT_A_PART_OFFSET}, "overlays/mcp2515-can0.dtbo") }

   4. finally, add an on-resource line for task upgrade.b (around line 328), note that the variable used in fat_write is different than for the previous steps:

      on-resource mcp2515-can0.dtbo { fat_write(${BOOT_B_PART_OFFSET}, "overlays/mcp2515-can0.dtbo") }

8. inside config/rpi3/fwup.conf find the file-resource definition for config.txt and change it to point at the one you copied into config/rpi3/config.txt

    file-resource config.txt {
        host-path = "${NERVES_APP}/config/rpi3/config.txt"
    }
   

9. edit config/rpi3/config.txt and define the mcp2515 overlay by adding:

    dtoverlay=mcp2515-can0,oscillator=16000000,interrupt=25
   

10. Inside your project directory: mix nerves.system.shell and when that loads, do the following:

    1. configure the kernel: mix linux-menuconfig

       1. Networking support -> <*> CAN bus subsystem support
       2. Networking support -> CAN bus subsystem support -> CAN Device Drivers -> CAN SPI interfaces -> <*> Microchip MCP251x SPI CAN controllers
       3. Select <SAVE>
       4. Select <EXIT> as many times as needed until you are dropped back in the nerves system shell

    2. safe the kernel config: make linux-savedefconfig

    3. IMPORTANT: you need to copy the newly saved kernel defconfig back into the rpi3 system using something like:

        cp build/linux-04c8e47067d4873c584395e5cb260b4f170a99ea/defconfig /nerves/env/nerves_system_rpi3/linux-4.4.defconfig
       

    4. OPTIONAL: add usefull can-related packages: mix menuconfig

       1. Target packages -> Networking applications -> iproute2
       2. Target packages -> Networking applications -> can-utils
       3. Select <SAVE>
       4. Select <Exit> until you are dropped back to shell

    5. save the package config: make savedefconfig

    6. exit to leave nerves.system.shell

11. mix compile NOTE: this will take forever the first time. on my four year old macbook pro this took about 4 hours

12. mix firmware

13. then depending on your project setup: mix firmware.burn / mix firmware.push ...

with any luck, you should now have a can0 device listed in /proc/net/dev on your rpi3. to pop into something similar to a console shell, run Nerves.Runtime.Shell.start from the iex prompt. From here you can do handy things like:

cat /proc/net/dev

and

ip link set can0 up type can bitrate 250000 (substitute 250000 with whatever bitrate you need for your vehicle)