From Mega2560 to Mega128 with Megacore = millis() problem

Hi, to be clear.. I'm far from an expert.
I have some code running on a Mega2560 pro board that I wanted to port to a Mega128 using Megacore to further integrate it in a HW design I have. Everything went well except 2 issues:

1/ I'm using Timer1 in a statemachine with also use of timer1-OVF for a 'timeout' and reset. Changing TIMSK1 = bit (TOIE1) to TIMSK = bit (TOIE1) solved the issue and that part of the code runs as expected now on the M128.

2/ I'm using millis() throughout another part of the code, but when I set TOIE1 (for timer1) => I can't use millis() anymore (which is supposed to use timer0) and I don't have a serial monitor to further understand what is happening on the M128...

The code below illustrates the issue => configure for the Mega2560 pro board and the led blinks, do it for the M128 and it stops :-/.

Anyone a clue please?

Thanks!

//const int ledPin =  44;               // Led on the M128 board
const int ledPin =  13;                 // Led on the mega2560  arduino board
int ledState = LOW;                     // ledState used to set the LED
unsigned long previousMillis = 0;  // last time LED was updated
const long interval = 500;           // interval at which to blink (milliseconds)

void setup() 
{ pinMode(ledPin, OUTPUT);         // set the digital pin as output:

  ////Timer1 setup: module configuration
  TCCR1A = 0;
  TCCR1B = 0;                                    // Disable Timer1 module
  TCNT1  = 0;                                     // Set Timer1 preload value to 0 (reset)

//  TIMSK = bit (TOIE1);                      // configuration of TIMSK for mega128 Timer1
  TIMSK1 = bit (TOIE1);                      // configuration of for a mega2560  arduino board
}

ISR(TIMER1_OVF_vect) 
{ //Case 0 of state machine in code to reset a decoding process
  TCCR1B = 0;
}  

void loop() 
{ unsigned long currentMillis = millis();
  if (currentMillis - previousMillis >= interval) 
  {
    previousMillis = currentMillis;
    if (ledState == LOW) ledState = HIGH;
    else ledState = LOW;
  }
  digitalWrite(ledPin, ledState);
}

Also posted here: From Mega2560 to Mega128 with Megacore = millis() problem · Issue #140 · MCUdude/MegaCore · GitHub

OK, issue is solved, was kindly helped “on the other side” and it seems I need to review my way of dealing directly with registers, but it is funny all worked well in the M2560…