samd21-usb-fixed

Thu, 11 Apr 2019 22:20:41 -0700
tags/snek

SAMD21 USB Fixed on Windows 7

I pretty clearly missed some details when reviewing the USB traces for the SAMD21 driver because I didn't see the IN requests to the IN-Interrupt endpoint of the device. These are supposed to be NAK'd by the device because it never generates any data for this endpoint.

However, I managed to mis-configure the hardware registers controlling this end point and set it up as an OUT-Interrupt endpoint instead. This causes the hardware to simply ignore any IN requests directed at the end point, so the host never sees a NAK packet. All three operating systems (Linux, Mac OS X and Windows) eventually give up trying to communicate with the end point, which causes no ill effects on Linux and Mac OS X.

On Windows, it causes the driver to stop sending IN packets to the regular IN-Bulk endpoint after it receives one packet. “It's inconceivable” I hear you cry, but then all can say is “It's Windows”, where inconceivable becomes reality.

All Fixed.

With that minor mistake fixed, Snek on the Metro M0 Express board is running great with all three operating systems.