TIM2_PCD_LO_BITS
int max_div = (1 << (TIM2_PCD_LO_BITS + TIM2_PCD_HI_BITS)) - 1;
(TIM2_PCD_HI_SHIFT - TIM2_PCD_LO_BITS);
tim2 |= (div >> TIM2_PCD_LO_BITS) << TIM2_PCD_HI_SHIFT;