delay() is inaccurate, averaging 500us too short. #60
Description
Since delay(n) waits for n ticks of the millisecond counter, any time already elapsed in the "current" millisecond isn't taken into account.
This was fixed a long time ago for the AVR, but it didn't make it into SAMD/SAM
arduino/ArduinoCore-avr@67c0a19#diff-ab397febf179e1982f4ee0758df4c982