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docs: Update CANBUS.md 

Recommend USB to CAN adapter and no longer recommend using the
waveshare rpi hat.

Recommend using allow-hotplug for all USB adapters.

Note bandwidth limitations when using USB to CAN bridge mode.

Note that a USB to CAN mcu is not a USB serial device.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>
This commit is contained in:
Kevin O'Connor 2023-05-20 16:36:25 -04:00
parent 5f0d252b40
commit 81e4636f42
1 changed files with 44 additions and 37 deletions
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docs/CANBUS.md
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@ -4,7 +4,7 @@ This document describes Klipper's CAN bus support.
## Device Hardware ## Device Hardware
Klipper currently supports CAN on stm32, same5x, and rp2040 chips. In Klipper currently supports CAN on stm32, SAME5x, and rp2040 chips. In
addition, the micro-controller chip must be on a board that has a CAN addition, the micro-controller chip must be on a board that has a CAN
transceiver. transceiver.
@ -14,44 +14,35 @@ and flash it to the target board.
## Host Hardware ## Host Hardware
In order to use a CAN bus, it is necessary to have a host adapter. In order to use a CAN bus, it is necessary to have a host adapter. It
There are currently two common options: is recommended to use a "USB to CAN adapter". There are many different
USB to CAN adapters available from different manufacturers. When
1. Use a choosing one, we recommend verifying that the firmware can be updated
[Waveshare Raspberry Pi CAN hat](https://www.waveshare.com/rs485-can-hat.htm) on it. (Unfortunately, we've found some USB adapters run defective
or one of its many clones. firmware and are locked down, so verify before purchasing.) Look for
adapters that can run Klipper directly (in its "USB to CAN bridge
2. Use a USB CAN adapter (for example mode") or that run the
[https://hacker-gadgets.com/product/cantact-usb-can-adapter/](https://hacker-gadgets.com/product/cantact-usb-can-adapter/)). There
are many different USB to CAN adapters available - when choosing
one, we recommend verifying it can run the
[candlelight firmware](https://github.com/candle-usb/candleLight_fw). [candlelight firmware](https://github.com/candle-usb/candleLight_fw).
(Unfortunately, we've found some USB adapters run defective
firmware and are locked down, so verify before purchasing.)
It is also necessary to configure the host operating system to use the It is also necessary to configure the host operating system to use the
adapter. This is typically done by creating a new file named adapter. This is typically done by creating a new file named
`/etc/network/interfaces.d/can0` with the following contents: `/etc/network/interfaces.d/can0` with the following contents:
``` ```
auto can0 allow-hotplug can0
iface can0 can static iface can0 can static
bitrate 500000 bitrate 1000000
up ifconfig $IFACE txqueuelen 128 up ifconfig $IFACE txqueuelen 128
``` ```
Note that the "Raspberry Pi CAN hat" also requires
[changes to config.txt](https://www.waveshare.com/wiki/RS485_CAN_HAT).
## Terminating Resistors ## Terminating Resistors
A CAN bus should have two 120 ohm resistors between the CANH and CANL A CAN bus should have two 120 ohm resistors between the CANH and CANL
wires. Ideally, one resistor located at each the end of the bus. wires. Ideally, one resistor located at each the end of the bus.
Note that some devices have a builtin 120 ohm resistor (for example, Note that some devices have a builtin 120 ohm resistor that can not be
the "Waveshare Raspberry Pi CAN hat" has a soldered on resistor that easily removed. Some devices do not include a resistor at all. Other
can not be easily removed). Some devices do not include a resistor at devices have a mechanism to select the resistor (typically by
all. Other devices have a mechanism to select the resistor (typically connecting a "pin jumper"). Be sure to check the schematics of all
by connecting a "pin jumper"). Be sure to check the schematics of all
devices on the CAN bus to verify that there are two and only two 120 devices on the CAN bus to verify that there are two and only two 120
Ohm resistors on the bus. Ohm resistors on the bus.
@ -95,22 +86,18 @@ canbus_uuid: 11aa22bb33cc
## USB to CAN bus bridge mode ## USB to CAN bus bridge mode
Some micro-controllers support selecting "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 during Klipper's "make menuconfig". This mode may allow one to use a
micro-controller as both a "USB to CAN bus adapter" and as a Klipper micro-controller as both a "USB to CAN bus adapter" and as a Klipper
node. node.
When Klipper uses this mode the micro-controller appears as a "USB CAN When Klipper uses this mode the micro-controller appears as a "USB CAN
bus adapter" under Linux. The "Klipper bridge mcu" itself will appear 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` as if it was on this CAN bus - it can be identified via
and configured like other CAN bus Klipper nodes. It will appear `canbus_query.py` and it must be configured like other CAN bus Klipper
alongside other devices that are actually on the CAN bus. nodes.
Some important notes when using this mode: 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 * It is necessary to configure the `can0` (or similar) interface in
Linux in order to communicate with the bus. However, Linux CAN bus Linux in order to communicate with the bus. However, Linux CAN bus
speed and CAN bus bit-timing options are ignored by Klipper. speed and CAN bus bit-timing options are ignored by Klipper.
@ -119,12 +106,32 @@ Some important notes when using this mode:
* Whenever the "bridge mcu" is reset, Linux will disable the * Whenever the "bridge mcu" is reset, Linux will disable the
corresponding `can0` interface. To ensure proper handling of corresponding `can0` interface. To ensure proper handling of
FIRMWARE_RESTART and RESTART commands, it is recommended to replace FIRMWARE_RESTART and RESTART commands, it is recommended to use
`auto` with `allow-hotplug` in the `/etc/network/interfaces.d/can0` `allow-hotplug` in the `/etc/network/interfaces.d/can0` file. For
file. For example: example:
``` ```
allow-hotplug can0 allow-hotplug can0
iface can0 can static iface can0 can static
bitrate 500000 bitrate 1000000
up ifconfig $IFACE txqueuelen 128 up ifconfig $IFACE txqueuelen 128
``` ```
* The "bridge mcu" is not actually on the CAN bus. Messages to and
from the bridge mcu will not be seen by other adapters that may be
on the CAN bus.
* The available bandwidth to both the "bridge mcu" itself and all
devices on the CAN bus is effectively limited by the CAN bus
frequency. As a result, it is recommended to use a CAN bus frequency
of 1000000 when using "USB to CAN bus bridge mode".
Even at a CAN bus frequency of 1000000, there may not be sufficient
bandwidth to run a `SHAPER_CALIBRATE` test if both the XY steppers
and the accelerometer all communicate via a single "USB to CAN bus"
interface.
* A USB to CAN bridge board will not appear as a USB serial device, it
will not show up when running `ls /dev/serial/by-id`, and it can not
be configured in Klipper's printer.cfg file with a `serial:`
parameter. The bridge board appears as a "USB CAN adapter" and it is
configured in the printer.cfg as a [CAN node](#configuring-klipper).