Idiots guide to hacking samd21 hardware

[illuminateddan]

Hi!
Here's the story... I have inherited 30+ boards featuring a SAMD21G18A, an esp-wroom2, ublox gps+ant, RFID reader, an accelerometer, flash memory, solar pwr management and bat charging circuits and some blinky leds. Awesome, right?
I have traced most of the chip numbers and how they are connected to the samd21, and I have bought a J-link to program the processor. This has been successful and I have blinky leds using atmel studio 7, and even successfully burnt a m0 feather bootloader (to test): Huzzah!

However: I have googled until my eyes are sore and cannot find the answers to these questions:

1. Given that the native USB port pins are attached to other components:
   a) if I burn an arduino bootloader, how can I upload code? Can I use the JTAG to upload sketches?
   b) there is already a header for the PB03/4:sercom5.0/5.1 broken out. Could I redefine the native USB to this?

Basically, I want to use the boards with arduino as its comfortable and resourced. Please point me to answers / links if you would be so kind! Attrached is the schematic of connections to the chip that I have discovered so far fyi.

[davidpruitt]

As far as I can tell there aren't any other pins that can be used for USB on the SAMD21. That basically means you won't be able to have a USB-serial port on any of these boards unless you manually scratch out some traces and resolder some stuff.

But yes you can still program the boards just fine. One possibility is to compile the Arduino sketch to a bin file, and then use Atmel Studio to deploy the bin file to the board, using your JLink programmer.