anchor.diff:        (setf (ldb (byte 1 +ahci-PxCMD-ST+) cmd) 1)
         (setf (ahci-port-register ahci port +ahci-register-PxCMD+) cmd))
       ;; Flush PxSERR.
  -    (setf (ahci-port-register ahci port +ahci-register-PxSERR+)
  -          (ahci-port-register ahci port +ahci-register-PxSERR+))
  +    (setf (ahci-port-register ahci port +ahci-register-PxSERR+) #xFFFFFFFF)
       ;; Clear any outstanding interrupts on this port.
       (setf (ahci-port-register ahci port +ahci-register-PxIS+)
             (ahci-port-register ahci port +ahci-register-PxIS+))
  
positive.code:   received-fis
    command-table
    (irq-latch (make-latch "AHCI Port IRQ Notifier"))
    lba48-capable
    sector-size
    sector-count)
  
negative.code:     (setf (ldb (byte 1 +ahci-ch-di-W+)
                 (physical-memref-unsigned-byte-32 cl +ahci-ch-descriptor-information+))
            (if write 1 0))
      (setf (ldb (byte 1 +ahci-ch-di-A+)
                 (physical-memref-unsigned-byte-32 cl +ahci-ch-descriptor-information+))
            (if atapi 1 0))
      ;; Point the PRDT 0 to the buffer.
      (setf (physical-memref-unsigned-byte-32 (+ ct +ahci-ct-PRDT+) +ahci-PRDT-DBA+) (ldb (byte 32 0) buffer)
            (physical-memref-unsigned-byte-32 (+ ct +ahci-ct-PRDT+) +ahci-PRDT-DBAU+) (ldb (byte 32 32) buffer))
  