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STM32F2 USB "both lines high"

Question asked by scott.gordon.001 on Jun 11, 2014
I have a curious behaviour with USB that I can't presently understand.

I have a dual CDC/VCP of an STM32F205 HS_FS USB port with the internal phy in FS mode.

When connected to a Linux machine, the USB enumerates and runs fine.
When connected to Windows 7 or 8.1, it enumerates OK, but then has "both lines high", I think repeatedly, though it could be continuous.

This seems to happen shortly after "set line coding" or "set line state", though not instantly.

An additional curiosity, I have essentially the same code on two projects, both have the "both lines high" condition, but one product functions whilst the other does not.

I wondered if anyone had seen an issue like this and could shine any light on it.


The non-working product turned out to be stack problem.

The both lines high problem remains on both products on Windows.
I'd been ignoring it as it seemed anyway to function, but I've returned to it because I think it might(!) be implicated in a slow response issue.