is there a reason using 2 separate usb endpoint for virtual com port example?

[vicki19880929]

Posted on October 05, 2013 at 00:46

I was checking out the usb virtual com port loopback example provided in STM32_USB-FS-Device_Lib_V4.0.0.  

When I looked into the usb endpoint (usb_endp.c or usb_conf.h), it defines EP3 (OUT) and EP1(IN) as the endpoints for bulk data in and data out.  I wonder if there's any reason using two endpoints instead of one?   According to RM0038, there are 8 bi-direction endpoints or 16 single-direction endpoints for stm32l-discovery.  Can't we combine the two single-direction endpoint of EP3 and EP1 into one bi-direction endpoint, just like the EP0 bi-directional endpoint?  Is there any limitation doing this?  

Thanks a lot!

[vicki19880929]

Posted on October 07, 2013 at 18:30

Anyone? I've given it a try by setting both at EP1_IN and EP1_OUT as bulk endpoint, but the virtual com port example didn't work at all.  Thanks.

[Tesla DeLorean]

Posted on October 07, 2013 at 18:38

Anyone?

Apparently no one with an answer.

[vicki19880929]

Posted on October 07, 2013 at 23:38

Thanks clive.  

I didn't change the direction in the usb descriptor so it couldn't function at all.  After I changed the descriptor file,  the bidirectional bulk endpoint is working.