The functions clockCyclesPerMicrosecond, clockCyclesToMicroseconds(a), microsecondsToClockCycles(a) are missing from Arduino.h. These functions/defines are present in the other cores (e.g. AVR, SAM, SAMD, ...).

Some libraries (e.g. Adafruit DHT_Sensor_Library, and others on GitHub) use one or more of these functions. This results in an undefined error when building for the Nano 33 BLE.

Do you consider this a bug in the core or an incorrect assumption that these are defined by some library creators?

If these should be defined in the core I'm happy to submit a PR to add them.