SAMD11 issues
After reviewing with Microchip, I think all of our SAMD11 issues had to do with its sensitivity to slowly-rising power. I had picked the wrong capacitor value in my final test in Kerala; I just updated that and tested it without trouble:
http://academy.cba.mit.edu/classes/embedded_programming/D11C/hello.D11C.blink.reset.png
This has an RC filter to slow the reset turn-on, and leaves off the clock pull-up that's usually not needed. I just tested and this works for me, can people who had SAMD11 issues try reproducing it?
It's using my 10->4 pin JTAG SWD header adapter, to save space and simplify routing:
http://academy.cba.mit.edu/classes/embedded_programming/SWD/hello.SWD.10-4.png