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candleLight_gsusb

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This is firmware for certain STM32F042x/STM32F072xB-based USB-CAN adapters, notably:

Of important note is that the common STM32F103 will NOT work with this firmware because its hardware cannot use both USB and CAN simultaneously. Beware also the smaller packages in the F042 series which map a USB and CAN_TX signal on the same pin and are therefore unusable !

This implements the interface of the mainline linux gs_usb kernel module and works out-of-the-box with linux distros packaging this module, e.g. Ubuntu.

Limitations

STM32G0B1-based devices are not yet supported by the mainline firmware. Support for these devices is discussed in https://github.com/candle-usb/candleLight_fw/pull/139 and https://github.com/candle-usb/candleLight_fw/pull/176.

STM32G431-based devices (e.g. CANable-MKS 2.0) are not yet supported.

Currently, the firmware sends back an echo frame to the host when the frame is written to the CAN peripheral, and not when the frame is actually sent successfully on the bus. This affects timestamps, one-shot mode, and other edge cases.

Known issues

Be aware that there is a bug in the gs_usb module in linux<4.5 that can crash the kernel on device removal.

Here is a fixed version that should also work for older kernels: https://github.com/HubertD/socketcan_gs_usb

The Firmware also implements WCID USB descriptors and thus can be used on recent Windows versions without installing a driver.

Building

Building requires arm-none-eabi-gcc toolchain.

sudo apt-get install gcc-arm-none-eabi

mkdir build
cd build
cmake .. -DCMAKE_TOOLCHAIN_FILE=../cmake/gcc-arm-none-eabi-8-2019-q3-update.cmake

# or,
# cmake-gui ..
# don't forget to specify the cmake toolchain file before configuring.
#
# compile all targets :

make

# OR, each board target is a cmake option and can be disabled before running 'make';
# OR, compile a single target , e.g.
make cantact_fw

#
# to list possible targets :
make help

Download Binaries

Prebuilt binaries can be downloaded by clicking CI. On the workflow overview page, select the latest workflow that ran on master branch. The firmware artifacts can downloaded by clicking them at the bottom of the page.

Flashing

Flashing candleLight on linux: (source: https://cantact.io/cantact/users-guide.html)

recommended simple method

method for reflashing a specific device by serial

fail-safe method (or if flashing a blank device)

Associating persistent device names

With udev on linux, it is possible to assign a device name to a certain serial number (see udev manpages and systemd.link). This can be useful when multiple devices are connected at the same time.

An example configuration :

 $ cat /etc/systemd/network/60-persistent-candev.link
[Match]
Property=ID_MODEL=cannette_gs_usb ID_SERIAL_SHORT="003800254250431420363230"

[Link]
# from systemd.link manpage:
# Note that specifying a name that the kernel might use for another interface (for example "eth0") is dangerous because the name assignment done by udev will race with the assignment done by the kernel, and only one
#   interface may use the name. Depending on the order of operations, either udev or the kernel will win, making the naming unpredictable. It is best to use some different prefix

Name=cannette99

( The serial number can be found with the lsusb utility). After reloading systemd units and resetting this board :

 $ ip a
....
59: cannette99: <NOARP,ECHO> mtu 16 qdisc noop state DOWN group default qlen 10
    link/can
 $

Hacking

Submitting pull requests

Typical command to run uncrustify on all source files (ignoring HAL and third-party libs): uncrustify -c ./uncrustify.cfg --replace --no-backup $(find include src -name "*.[ch]")

Profiling

Not great on cortex-M0 cores (F042, F072 targets etc) since they lack hardware support (ITM and SWO). However, it's possible to randomly sample the program counter and get some coarse profiling info.

For example, openocd has the profile command (see https://openocd.org/doc/html/General-Commands.html#Misc-Commands), e.g.

profile 5 test.out 0x8000000 0x8100000

(from inside gdb, the command needs to be prefixed with monitor to forward it to openocd, i.e. monitor profile 5 ......

The .out file can then be processed with gprof <firmware_name> -l test.out

Links to related projects