How to control a timer in Arduino?

Question

Arduino

There is an Arduino UNO with an atmega328p on board. I'm trying to set a timer for 250 microseconds.
I am using the following code:

void setup() 
{ 
  DDRC = 0xFF;
  DDRB = 0xFF;

TCNT1 = 0;
  TCCR1B = /*_BV(CS11)|*/_BV(CS10);
TCNT1 = 0;
  //TIMSK1 = _BV(TOIE1);

TIMSK1 |= (1<<TOIE1);

        //-TIMER1_OVF_vect
   
    sei();
  
}//setup()
 
void loop() 
{ 
}
  
volatile uint8_t pp = 0;

ISR(TIMER1_OVF_vect)
{
    pp = ~pp;
    PORTC = pp;
    PORTB = pp;
}

Everything is fine, the timer has started. But only prescaler changes lead to nothing - the frequency is always 2 milliseconds. What's wrong with the timer?
UDP: I look at the changes with an oscilloscope, and not with something else.

Answer 1

The arduino environment uses timers for its tasks - the first millis timer, the second pwm.
You need to comment them out in the arduino code first and then use them.