kopia lustrzana https://github.com/micropython/micropython
0f6f86ca49
Prior to this commit the USB CDC used the USB start-of-frame (SOF) IRQ to regularly check if buffered data needed to be sent out to the USB host. This wasted resources (CPU, power) if no data needed to be sent. This commit changes how the USB CDC transmits buffered data: - When new data is first available to send the data is queued immediately on the USB IN endpoint, ready to be sent as soon as possible. - Subsequent additions to the buffer (via usbd_cdc_try_tx()) will wait. - When the low-level USB driver has finished sending out the data queued in the USB IN endpoint it calls usbd_cdc_tx_ready() which immediately queues any outstanding data, waiting for the next IN frame. The benefits on this new approach are: - SOF IRQ does not need to run continuously so device has a better chance to sleep for longer, and be more responsive to other IRQs. - Because SOF IRQ is off, current consumption is reduced by a small amount, roughly 200uA when USB is connected (measured on PYBv1.0). - CDC tx throughput (USB IN) on PYBv1.0 is about 2.3 faster (USB OUT is unchanged). - When USB is connected, Python code that is executing is slightly faster because SOF IRQ no longer interrupts continuously. - On F733 with USB HS, CDC tx throughput is about the same as prior to this commit. - On F733 with USB HS, Python code is about 5% faster because of no SOF. As part of this refactor, the serial port should no longer echo initial characters when the serial port is first opened (this only used to happen rarely on USB FS, but on USB HS is was more evident). |
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