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usb_canbus: Initial support for USB to CAN bridge mode

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Support a USB interface that shows up as a canbus adapter to linux.
Route both local and real canbus packets over that interface.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>
This commit is contained in:
Kevin O'Connor 2022-06-08 21:03:11 -04:00
parent c8cc98ce5d
commit 790ff4d8d7
8 changed files with 782 additions and 15 deletions
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31
docs/CANBUS.md
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@ -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.