The Analog to Digital Converter in the SAMD21 is specified to run with a clock frequency from 30 to 2,100 kHz. The Arduino Library configures the ADC clock to be the 48 MHz system clock divided by 256, or 187.5 kHz, or a clock period of 5.33 µs. The conversion time is 7 clock periods, …
I performed surgery on the Arduino Library. Yes, it is a risky task. I had to modify five source files, but the changes are conditionally compiled. I had previously added another “board” that is the Arduino Nano Every with a 20MHz clock so I could easily select it. Now I’ve gotten rid of the ATMEGA328 …