Timer1 impacts Timer0 on Arduino Nano ?

Projects Programming
5

Hi, as requested :

So, when i compile with timer1 from 65517 to 65520 (and more i guess), millis() return 0.
Below, it works correctly.

Is anyone can help me to understand this behavior ?
Patrick

//===============================================================================================================
// ARDUINO
//===============================================================================================================
//#define  TIMER1_COUNTER   49536     // = 65536-16MHz/  1/   1kHz --> 16000 /  1000µs // works
//#define  TIMER1_COUNTER   63936     // = 65536-16MHz/  1/  10kHz -->  1600 /   100µs // works
//#define  TIMER1_COUNTER   65376     // = 65536-16MHz/  1/ 100kHz -->   160 /    10µs // works
//#define  TIMER1_COUNTER   65456     // = 65536-16MHz/  1/ 200kHz -->    80 /     5µs // works
//#define  TIMER1_COUNTER   65472     // = 65536-16MHz/  1/ 250kHz -->    64 /     4µs // works
//#define  TIMER1_COUNTER   65504     // = 65536-16MHz/  1/ 500kHz -->    32 /     2µs // works
//#define  TIMER1_COUNTER   65510     // = 65536-16MHz/  1/ 615Hz -->     26 / 1.625µs // works
//#define  TIMER1_COUNTER   65515     // = 65536-16MHz/  1/ 762kHz -->    21 /1.3125µs // works
//#define  TIMER1_COUNTER   65516     // = 65536-16MHz/  1/ 800kHz -->    20 /  1.25µs // works
#define  TIMER1_COUNTER   65517     // = 65536-16MHz/  1/ 842kHz -->    19 /1.1875µs // ISSUE !!!
//#define  TIMER1_COUNTER   65518     // = 65536-16MHz/  1/ 889kHz -->    18 /1.1250µs // ISSUE !!!
//#define  TIMER1_COUNTER   65519     // = 65536-16MHz/  1/ 941kHz -->    17 /1.0625µs // ISSUE !!!
//#define  TIMER1_COUNTER   65520     // = 65536-16MHz/  1/   1MHz -->    16 /     1µs // ISSUE !!! --> My target

volatile uint32_t   tickms = 0;
//---------------------------------------------------------------------------------------------------------------
void myIRQTimer() {
  noInterrupts();           // disable all interrupts
  TCCR1A = 0;               // initialize timer1 
  TCCR1B = (1 << CS10);     // 1 prescaler 

  TCNT1 = TIMER1_COUNTER;   // preload timer
  TIMSK1 |= (1 << TOIE1);   // enable timer overflow interrupt
  interrupts();             // enable all interrupts
}
//---------------------------------------------------------------------------------------------------------------
ISR(TIMER1_OVF_vect) {      // interrupt service routine
  tickms++;
  TCNT1 = TIMER1_COUNTER;   // preload timer
}
//---------------------------------------------------------------------------------------------------------------
void setup() {
  myIRQTimer();         // Configure Timer1
  Serial.begin(115200);
  Serial.print(F("Timer1 Bug ?\n"));
}

void loop() {
  Serial.println(millis());
}
//---------------------------------------------------------------------------------------------------------------