PORTS Forum
Ports and Interfaces => USB => Topic started by: DeeShia on August 21, 2014, 09:14:13 pm
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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:
(http://s18.postimg.org/rwscqllzd/Capture.jpg) (http://postimg.org/image/hmpxrcw3p/full/)
upload image online (http://postimage.org/)
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!
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(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.
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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