wp_apu_read
sc->record.current = wp_apu_read(sc, sc->record.num, APUREG_CURPTR);
sc->play.current = wp_apu_read(sc, sc->play.num, APUREG_CURPTR);
pos = wp_apu_read(ch->sc, ch->num, APUREG_CURPTR);
cp = wp_apu_read(ch->sc, ch->num, APUREG_CURPTR);
diff = wp_apu_read(ch->sc, ch->num+1, APUREG_CURPTR) - cp;
wpreg_t wp_apu_read(struct maestro_softc *, int, int);