arduino - Stop timer set new value and start again AVR (Interrupt) -

i have avr mcu.
playing timer now.
need ? have timer counting frequency. in each interrupt incrementing variable, , somewhere need check value of variable , if equals 100, need stop timer count, set new value frequency , continue counting down.
cannot how stop timer , set new value compare.
have tried select no clock source using mux selector register, continue count up.
correct way this. here code

// arduino timer ctc interrupt example // www.engblaze.com  // avr-libc library includes #include <avr/io.h> #include <avr/interrupt.h>  #define ledpin_up 9 #define ledpin_down 8 int current_value = 0; void setup() {    serial.begin(9600);      // pinmode(ledpin_up, output);      // initialize timer1     cli();          // disable global interrupts     tccr1a = 0;     // set entire tccr1a register 0     tccr1b = 0;     // same tccr1b      // set compare match register desired timer count:    // ocr1a = 3123;     ocr1a = 1562;     // turn on ctc mode:     tccr1b |= (1 << wgm12);     // set cs10 , cs12 bits 1024 prescaler:     tccr1b |= (1 << cs10);     tccr1b |= (1 << cs12);     // enable timer compare interrupt:     timsk1 |= (1 << ocie1a);     // enable global interrupts:     sei(); }  void loop() {     //digitalwrite(ledpin_up, current_value);   serial.println(current_value);        if(current_value==255) {       tccr1b |= (0 << cs10);       tccr1b |= (0 << cs12);       serial.println("reseting timer");     } }  isr(timer1_compa_vect) {     current_value++;  } 

  tccr1b |= (0 << cs10);   tccr1b |= (0 << cs12); 

does not expecting. since using "or" |, value placed 0|1 1, not 0 desire.

the usual way clear bit is

  tccr1b &= ~(1 << cs10); 

to clear 2 bits @ once, use

  tccr1b &= ~(1 << cs10 | 1 << cs12); 

as counting down, want use variable indicate direction going, , use variable in isr. perhaps,

int dir = 1;  isr(timer1_compa_vect) {     current_value += dir; } 

and change dir -1 when want count down instead.