Posted on April 17, 2012 at 09:03Use CDC example as a template. There are two BULK endpoints. For better transfer speed CDC example would require small modifications.
1) Change VCOMPORT_IN_FRAME_INTERVAL to lower value. I'm not sure is value = 1 is suitable when transfer needs to be bidirectional, so I've used value = 2. It won't make much difference though.
2) Increase USART_RX_DATA_SIZE. I've used 8192 bytes (2 x 4 kB), but I think that there would be no speed difference with values above 4096 B (maximum number of data would be transmitted in every or almost every frame).
3) Modify Handle_USBAsynchXfer so it wouldn't transmit data unless half of the USART_Rx_Buffer would be full. Thus after each SOF maximum number of bytes would be sent. If there is a change that buffer would be filled with low speed or not filled at all for some time then some kind of timeout would be needed here that would cause transmitting whatever is in buffer already - you may know this problem if you've used USB to UART converters before.
On a PC side make sure that application is constantly ready to accept new data. I've used libusb, so I've used combination of usb_submit_async/usb_reap_async to enqueue multiple read requests. I guess with WinUSB that could be made with overlapped I/O.
I wasn't interested in high PC to device speed, so I haven't any tips on reverse direction.
If you are using STM32F103C8T6 or similar, then
http://tomeko.net/miniscope_v2c/
source code (CoIDE+gcc) might be helpful. Otherwise better start with clean CDC example - I've removed some code not related to this specific MCU from source code to make it easier to understand.
