USB "fast buffer switching" on stm32 usbfs devices #6352
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Replace the set_stat_x_bits() functions with a single calc_epr_bits() function. This new function supports setting bits other than the stat field in the epr register. Signed-off-by: Kevin O'Connor <[email protected]>
The usbfs device supports two buffers for each endpoint - typically one for rx and one for tx. Add support for explicit handling of both buffers. This is in preparation for improved "double buffering" support. Signed-off-by: Kevin O'Connor <[email protected]>
Implement the usbfs fast buffer switching mechanism on the "bulk out" endpoint. This can improve the overall USB throughput and bus utilization. Signed-off-by: Kevin O'Connor <[email protected]>
Implement the usbfs fast buffer switching mechanism on the "bulk in" endpoint. This can improve the overall USB throughput and bus utilization. Signed-off-by: Kevin O'Connor <[email protected]>
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This adds support for "fast buffer switching" on the USB peripheral of stm32f1, stm32g0, and stm32f0 devices.
This feature can improve the USB transfer rates on these devices. It's unlikely to be noticed on traditional emulated serial over USB setups, but it can have a notable impact when using USB to CANBUS bridge configurations.
When the micro-controller is configured to behave as a canbus adapter, the gs_usb linux kernel protocol requires many small USB packets to be transferred. Optimizing the USB buffer handling can notably improve overall transfer rates. In particular, I've found that, prior to these changes, the USB to CANBUS bridge setup was bottlenecked by USB transfers on some machines (such as the rpi3) - thus preventing those setups from utilizing the full bandwidth of 1Mbit/s canbus.
-Kevin