INP
tmp = INP(LSR);
tmp = INP(MSR);
tmp = INP(IIR);
tmp = INP(RBR);
OUTP(LCR, INP(LCR) | LCR_DLAB);
OUTP(LCR, INP(LCR) & ~LCR_DLAB);
while ((INP(LSR) & LSR_THRE) == 0)