Generic Clock 3 in SAMD21 core

[Jeremy Gilbert]

Arduino Devs -

I'm playing around with with the PTC peripheral which needs a relatively fast (400-4000kHz) clock. I was thinking of using generic clock generator 3 for this with a 2:1 divider feed by OSC8M. Currently this clock is configured in SAMD21 but I cannot locate any part of the code that uses it. PWM, Tone and Sercom all appear clocked from GCLK_0. Is that correct or is it being used in some non-obvious way?

Jeremy