AHCI_P_SACT
AHCI_WRITE(sc, AHCI_P_SACT(chp->ch_channel), 1U << xfer->c_slot);
AHCI_READ(sc, AHCI_P_SACT(chp->ch_channel)),
sact = AHCI_READ(sc, AHCI_P_SACT(chp->ch_channel));