SER_DSR
sc->sc_msr |= SER_DSR;
msr |= SER_DSR;
sc->sc_msr |= SER_DSR;
*p_msr |= SER_DSR;
sc->sc_msr |= SER_DSR;
if (ISSET(bits, SER_DSR)) {
SET(rbits, SER_DSR);
if (sc->sc_msr & SER_DSR) {
sigon |= SER_DSR;
msr |= SER_DSR;
sc->sc_msr |= SER_DSR;
#define SER_DDSR SER_DELTA(SER_DSR)