Add a USB message queue to USB to CANbus bridge code #6354
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KevinOConnor
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Rename the internal variable names. This is in preparation for support of a USB message queue. Signed-off-by: Kevin O'Connor <[email protected]>
Read USB messages arriving from the host into a queue. This makes it less likely that USB "bulk out" packets will be NAK'ed on the USB bus, which improves USB bus utilization. Signed-off-by: Kevin O'Connor <[email protected]>
Prioritize sending responses back to the host over transmitting new messages from the host. Otherwise, the gs_usb host usb acknowledgments could saturate the usb bandwidth for extended periods. Signed-off-by: Kevin O'Connor <[email protected]>
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The current Klipper USB to CANbus bridge code will stop reading messages from the USB bus if it becomes busy sending messages on the USB bus. This was implemented as a flow control system to prevent bandwidth generated from host messages swamping message traffic received from the physical canbus.
Unfortunately, this flow control system has a notable performance impact. The low-level USB hardware layer will keep sending messages until the device acknowledges them. So, if the CANbus bridge code does not read USB messages, the retransmits continue to consume bandwidth - bandwidth that would be better utilized in sending messages from the device to the host.
This PR adds a small USB message queue to the USB to CANbus bridge code. The Linux gs_usb driver will only send 10 pending packets before it pauses transmissions. So, a small queue that stores these messages can help avoid low-level USB message resends.
This PR can notably improve the performance of the Klipper USB to CANbus bridge code.
-Kevin