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Tools.md

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This document describes some available tools that may be useful for testing and debugging the can2040 code. These tools may also facilitate development and may be useful as coding examples.

Klipper

The Klipper code utilizes can2040 for micro-controller CAN bus communication on rp2040 chips.

Klipper can also be compiled in a USB to CAN bus bridge mode so that an rp2040 device appears as a standard Linux USB to CAN bus adapter (using the "gs_usb" Linux driver). Compiling the Klipper micro-controller code in this mode may be useful for CAN bus diagnostics even when not using Klipper. See the Klipper installation instructions for the full installation instructions. Briefly, on a Raspberry Pi computer the installation involves:

  1. Download the Klipper code (git clone https://github.com/Klipper3d/klipper).
  2. Install compiler tools (sudo apt-get update && sudo apt-get install build-essential libncurses-dev libusb-dev libnewlib-arm-none-eabi gcc-arm-none-eabi binutils-arm-none-eabi libusb-1.0 pkg-config).
  3. Configure the micro-controller software (make menuconfig). Select "Enable extra low-level configuration options", select "Raspberry Pi RP2040" as the micro-controller, select "No bootloader", select "USB to CAN bus bridge", set the appropriate gpio pins for CAN RX and CAN TX, and set the desired CAN bus frequency.
  4. Build the micro-controller software (make).
  5. Place the rp2040 micro-controller in bootloader mode and flash the software (make flash FLASH_DEVICE=2e8a:0003).

Once the Klipper micro-controller code is running on the rp2040 it is possible to use the Linux can-utils tools. Briefly:

  1. Install the can-utils package (sudo apt-get update && sudo apt-get install can-utils).
  2. Bring up the "can0" Linux interface (eg, sudo ip link set can0 up type can bitrate 1000000). Note that Klipper currently uses the CAN bus frequency set during "make menuconfig" and the value set in Linux is ignored.
  3. In one window run the candump utility to show all packets read by the interface (eg, candump -t z -Ddex can0,#FFFFFFFF).
  4. In another window, send packets on the CAN bus (eg, cansend can0 123#121212121212).

CanBoot

The CanBoot code implements a cross-platform bootloader that supports flashing an rp2040 micro-controller over CAN bus. It utilizes can2040 on rp2040 chips.

Testing CAN bus

Note that can2040 (and CAN bus in general) requires a functional hardware bus for proper message generation. At a minimum, can2040 requires a functioning transceiver, functioning "CAN H" and "CAN L" wiring, two 120 Ohm resistors on that wiring, at least one additional CAN bus enabled chip with its own transceiver, and all chips much be configured with the same CAN bus frequency. If any of the above hardware is missing or not properly connected/configured then the bus will not function correctly; not even for debugging purposes.

Testing with Raspberry Pi Pico board

It is possible to use a Raspberry Pi Pico board with a CAN bus transceiver board for testing. The following picture shows an example wiring with a "Waveshare SN65HVD230 CAN Board":

pico-wiring

In the above picture, 3.3V on the transceiver board is wired to 3.3V on the Pico, GND is wired to GND, CAN Rx is wired to GPIO4, and CAN Tx is wired to GPIO5. (Note that the "Waveshare SN65HVD230 CAN Board" has a builtin 120 Ohm resistor between the CANH and CANL wires which is not easy to remove.)

Sigrok logic analyzer

The Sigrok Pulseview software along with a low-cost logic analyzer can be useful for diagnosing CAN bus signaling.

One can often find "USB logic analyzers" for under $15 (US pricing as of 2023). These devices are often listed as "Saleae logic clones" or as "24MHz 8 channel USB logic analyzers".

pulseview-canbus

The above picture was taken while using pulseview with a "Saleae clone" logic analyzer. The Sigrok and pulseview software was installed on a desktop machine (also install the "fx2lafw" firmware if that is packaged separately). The CH0 pin on the logic analyzer was routed to the rp2040 CAN Rx line, the CH1 pin was wired to the CAN Tx pin, and GND was wired to GND. Pulseview was configured to only display the D0 and D1 lines (red "probe" icon center top toolbar). The number of samples was set to 5 million (top toolbar) and the sample rate was set to 24Mhz (top toolbar). The CAN decoder was added (yellow and green "bubble icon" right top toolbar). The D0 channel was labeled as RX and set to trigger on a falling edge (click on black D0 label at left). The D1 channel was labeled as TX (click on brown D1 label at left). The CAN decoder was configured for 1Mbit rate (click on green CAN label at left). The CAN decoder was moved to the top of the display (click and drag green CAN label). Finally, the capture was started (click "Run" at top left) and a packet was transmitted on the CAN bus (cansend can0 123#121212121212).

The logic analyzer can provide an independent tool for capturing packets and verifying bit timing.