A simple program for the Digispark Pro for reading in 10 digital inputs and mapping them to joystick buttons.

Atari2600USB.ino

#include "DigiJoystick.h"

char BUTS[] = { 6, 5, 2, 1, 0, 7, 8, 9, 10, 11 };
void setup() {
  for (int i = 0; i < 10; i++) {
    pinMode(BUTS[i], INPUT);
  }
}

void loop() {
  DigiJoystick.delay(50);
  int p = 0;
  for (int i = 0; i < 10; i++) {
    p |= digitalRead(BUTS[i])<<i;
  }
  DigiJoystick.setButtons((char)(p&0xFF), (p>>8)&0xFF);
}