USB Virtual COM Port - Enumeration Problem

[DeeShia]

Hello,

I am trying to implement a USB virtual COM port on an embedded device using the CDC ACM class.  I am an encountering an issue after sending the configuration descriptor in enumeration.  After the descriptor is sent, activity on the bus halts.  The configuration descriptor is sent successfully, and I don't see anything that indicates an error in the control transfer.  This is what it looks like from a protocol analyzer capture:


upload image online

My question is if there's a likely cause for this issue (my first instinct was that the descriptor wasn't set up correctly) that I'm not picking up on.  I've only been working with USB for a few months so I'm not experienced with common problems that developers run into.

Thanks!

[Jan Axelson]

(Assuming Windows) do you have an INF file and does Windows find it or ask for its location?

setupapi.dev.log in Windows/inf might have useful information.

[Nik]

Hi DeeShia,

I too had problem initially getting the enumeration right.

I found out that the config descriptor is of 67 bytes but the control transfer was of 64 bytes. I had to send the next 3 bytes in one more transfer. Just check if that is the case with you too.

Here is the link for my issue and the solution:
http://janaxelson.com/forum/index.php?topic=1306.msg5908#msg5908

Cheers !
Nik