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diff --git a/docs/CANBUS.md b/docs/CANBUS.md index fc85dc76..90efacf5 100644 --- a/docs/CANBUS.md +++ b/docs/CANBUS.md @@ -91,3 +91,34 @@ the CAN bus to communicate with the device - for example: [mcu my_can_mcu] canbus_uuid: 11aa22bb33cc ``` + +## USB to CAN bus bridge mode + +Some micro-controllers support selecting "USB to CAN bus bridge" mode +during "make menuconfig". This mode may allow one to use a +micro-controller as both a "USB to CAN bus adapter" and as a Klipper +node. + +When Klipper uses this mode the micro-controller appears as a "USB CAN +bus adapter" under Linux. The "Klipper bridge mcu" itself will appear +as if was on this CAN bus - it can be identified via `canbus_query.py` +and configured like other CAN bus Klipper nodes. It will appear +alongside other devices that are actually on the CAN bus. + +Some important notes when using this mode: + +* The "bridge mcu" is not actually on the CAN bus. Messages to and + from it do not consume bandwidth on the CAN bus. The mcu can not be + seen by other adapters that may be on the CAN bus. + +* It is necessary to configure the `can0` (or similar) interface in + Linux in order to communicate with the bus. However, Linux CAN bus + speed and CAN bus bit-timing options are ignored by Klipper. + Currently, the CAN bus frequency is specified during "make + menuconfig" and the bus speed specified in Linux is ignored. + +* Whenever the "bridge mcu" is reset, Linux will disable the + corresponding `can0` interface. Generally, this may require running + commands such as "ip up" to restart the interface. Thus, Klipper + FIRMWARE_RESTART commands (or regular RESTART after a config change) + may require restarting the `can0` interface. |