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How do I know if the USB port (host mode) is working?

Question asked by cuneo.john on May 9, 2014
Latest reply on May 13, 2014 by cuneo.john
I'm using the F105 series Stm32, and if my grab of the USB protocol being correct, the USB works on polling mechanism which means when idle, there should be regular frame of data on the DM/DP.

The thing is, when I probed both DM/DP, I had no reading on my oscilloscope other than seemingly random, below 0.5V very wide pulses, which I'm pretty sure is noise since A, it's well below 3.3v and B, it looks nothing like NRZI wave forms.

I'm fully aware that I could be wrong in A, for saving power's sake, there may not ever be any "polling frame" (quoted because such term may not be legit) UNLESS a device is plugged in AND properly enumerated, which I have no way to find out since I don't even know whether my USB port can detect devices that's been plugged in. And B, my entire understanding of the polling mechanism maybe wrong.

I remembered quite clearly what the polling frame was like when a few months ago I was probing a computer's USB port, and I'm fairly sure no device was attached, or I wouldn't be able to probe the USB port.

Any ideas? Can anyone please help me?

To be more specific, the 


always returns zero, which means it can't detect my HID device, which has been tested on various comps to be fine.