Right now the utime module just has sleep functions, but it would be very useful to add at least a ticks_ms function that returns a monotonically increasing millisecond tick count (at least increasing until it overflows and wraps around). This is handy for loops and such that need to know how much time has elapsed since the previous iteration. The ESP8266 port has a ticks_ms, ticks_us, etc. functions that are a good model to follow.

To implement this we probably want to use the SysTick counter and expose its value with the MicroPython HAL ticks function (currently just implemented to return 0). Poking around the ASF for the M0 I don't see many handy functions for it so might need to just deal with the SysTick registers, etc. directly.