I made a board for my project based on Arduino Pro Mini. The problem is, that I had to put the LED on pin 4 instead of pin 13.
What setting do I have to change to make pin 4 the default one? Or do I have to write my own Board Library?
Following on from Juraj's answer:
The blinking while uploading makes the bootloader. Arduino Mini uses Optiboot. The source codes are on GitHub. You would need to change the pin in pin_defs.h and make the bootloader. Then flash it to the 328p with a programmer over ICSP.
#define LED B5
As you can see it is currently set to
B5. This is the fifth bit in port B which corresponds to pin 13
Pin 4 corresponds to
PORTD bit 4, so the line would become
#define LED D4
The Arduino digital pins are connected to three different banks of 8 bits, known as ports (
PORTB and PORTC`). To see their relation, refer to this table from Arduino Playground - Pins