ICR_ACKNAK
if (reg & (ICR_ACKNAK | ICR_STOP)) {
reg &= ~(ICR_START | ICR_ACKNAK | ICR_STOP);
reg &= ~(ICR_STOP | ICR_ACKNAK);
reg &= ~(ICR_START | ICR_STOP | ICR_ACKNAK);
reg |= ICR_ACKNAK | ICR_STOP;
reg &= ~(ICR_START | ICR_STOP | ICR_ACKNAK);