Looking for ATMEGA328 hardware definitions (PORT,DDR etc)
In the datasheet, available from Microchip's website.
Manufacturer's page of the ATmega328P: https://www.microchip.com/wwwproducts/en/ATmega328P for the datasheet.
Arduino has pin definitions in pins_arduino.h.
The PORTB definitions are in iom328p.h which is part of the toolchain. I think it is part of the avr-libc, but I don't know where that is online.
my bad... using Due configuration instead of Atmega328