CLK_TBG_DIV1_SHIFT
prev_d1d2 = ((val >> CLK_TBG_DIV1_SHIFT) & CLK_TBG_DIV1_MASK) *
val &= ~(CLK_TBG_DIV1_MASK << CLK_TBG_DIV1_SHIFT);
val |= d1 << CLK_TBG_DIV1_SHIFT;