I didn't manage to get it to work on a GBA.

However on a Gameboy pocket I had to start with the custom logo rom instead of the nintendo logo rom and the delay is 500ms.

Thanks for your reply.

I'm using a purple Gameboy Color CGB-001.

That's strange indeed.

I'm using this simple code I wrote on Arduino and it works.

int ADR1 = 3; // A15 or A16
int ADR2 = 4; // A16 or A17


void setup() {

pinMode(ADR1, OUTPUT); // Pin 11 as Output
  pinMode(ADR2, OUTPUT); // Pin 12 as Output
  
  

  
digitalWrite(ADR1, HIGH);
 digitalWrite(ADR2, LOW);

delay(99);

digitalWrite(ADR1, LOW);
 digitalWrite(ADR2, LOW);

 
}

  void loop() {



  }

I'm gonna try the way of GB Dev FAQs as you stated to see if it works on a GBA.

Did you maybe mix GB Pocket with GB Color? The simple ROM swap scheme you described is the same as in nanoloop and only works with DMG and GB Pocket.

From GB DEV FAQs:

I haven't tried this, but I guess it's the same for GBA.

Hello there,

I actually managed to boot a game with a custom boot logo on a Gameboy, since it reads this part twice, once for VRAM and once to check that it's correct.

So I've used an attiny85 to select the rom with the custom logo then a delay of 100ms then the rom to boot up, it works perfectly on a gameboy and gameboy color. (I've used arduino to program the chip)

However I couldn't find how to do it for a Gameboy Advance, the delay isn't the same (around 400ms) hence I still can't boot the game with the full custom logo.

I was wondering if it's possible on a GBA.

Regards