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usbSofCount doesn't increment every millisecond

Posted: Fri Feb 15, 2008 2:29 pm
by iphi

my understanding is that usbSofCount should increment every millisecond.
Well, I tried this on my Easylogger hardware and I added a feature so I can read usbSofCount via USB.

I find that usbSofCount increments only very rarely, not even every second, sometimes more often depending on the USB traffic.

What am I doing wrong?

Regards, Thomas

Posted: Fri Feb 15, 2008 3:51 pm
by christian
In reality, usbSofCount increments on every interrupt which can't be interpreted as the start of a valid USB message. If you wire the interrupt to USB D+, this is roughly every Start Of Frame. Otherwise it's just garbage.