I have written a program which derives `microbit.running_time()` maximum. When `last` is greater than `microbit.running_time()` it stops and reports `last`.
The value it reports is 3200432, which is the maximum within 500ms or so.
What is the maximum value for running time? I thought it would be an unsigned int16 or unsigned int32.
How many bits wide is `microbit.running_time()` ?
Is it signed?