SAMD21E board ...SAM_BA bootloader uploads/verifies, no USB?

Discussions around product based on ARM Cortex M0+ core.

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Joined: Wed Apr 27, 2016 8:38 pm

SAMD21E board ...SAM_BA bootloader uploads/verifies, no USB?

Wed Apr 27, 2016 9:01 pm

OK, puzzled; sorry to ask but not sure where to turn. I've designed a small board using a SAMD21E18A using the Atmel-ICE debugger with SWD to connect.

Plugging the board in via USB (and verifying that the four USB pins connect from the end of the cable to the right places on the SAMD21), and plugging in the ICE, I can get device information, read and write to the chip, etc. A tiny sample program could be debugged in the studio and stepped through, etc. I can happily upload the SAM_BA bootloader for the chip...

...but it is completely unrecognized by the computer; it doesn't even make a "you plugged in a USB device" message. The USB powers up the board just fine, but... nothing. I can still communicate with the ICE, but the USB is dead.

It's worth noting that SOMETHING is slightly wrong, because my 3.3v regulator appears to be putting out 4.07v, which I can't work out. But while I sort that business out--is there any way to diagnose what's gone wrong with the USB?
Posts: 3
Joined: Fri Apr 22, 2016 8:24 am

Re: SAMD21E board ...SAM_BA bootloader uploads/verifies, no

Wed Jun 01, 2016 9:35 am

Better late than never...

It looks like the 5V from your USB cable is being put directly on a device pin. The protection diode inside the chip would short that to the 3.3V supply with about a 0.8V drop, which matches pretty well with what you're measuring. It may be any chip it's connected to that's powered from 3.3V, not necessarily the processor.

The computer won't tell you there's a device there unless it enumerates properly. You'd need working USB device code running on the chip. Simply drawing power from the USB port won't trigger anything.

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