What is the fastest way to read/write GPIOs on SAMD21 boards?

[Koepel]

@John41234

I have read that arduino's digitalread and digitalwrite are very slow on some samd21 boards

Where did you read that ?
What is slow for you ? 25 milliseconds or 2 picoseconds ?

Let me write the opposite for you:
The SAMD branch of Arduino boards (MKR Zero and others) have a fast digitalRead() and digitalWrite(). For the AVR branch of Arduino boards (Uno and others) there a benefit to use direct I/O instructions, but for the SAMD branch not so much.

So now you can say that you have read that the digitalread() and digitalWrite() are fast for SAMD boards