anchor.diff:  (defvar *debug-serial-tx-buffer*)
   (defvar *debug-serial-tx-buffer-head*)
   (defvar *debug-serial-tx-buffer-tail*)
  -(defvar *debug-serial-rx-buffer*)
  -(defvar *debug-serial-rx-buffer-head*)
  -(defvar *debug-serial-rx-buffer-tail*)
  +(defvar *debug-serial-rx-fifo*)
   (defvar *debug-serial-lock*)
   (defvar *serial-at-line-start*)
   
  
positive.code: (defun debug-serial-stream (op &optional arg)
    (ecase op
      (:read-char (debug-serial-read-char))
      (:clear-input)
      (:write-char (debug-serial-write-char arg))
      (:write-string (debug-serial-write-string arg))
      (:force-output)
  
negative.code:       (do ()
            ((not (logbitp +serial-lsr-data-available+
                           (sys.int::io-port/8 (+ *debug-serial-io-port* +serial-LSR+)))))
          (fifo-push (sys.int::io-port/8 (+ *debug-serial-io-port* +serial-RBR+))
                     *debug-serial-rx-fifo*
                     nil))
        ;; Refill the TX FIFO when it becomes empty.
        (when (logbitp +serial-lsr-thr-empty+
                       (sys.int::io-port/8 (+ *debug-serial-io-port* +serial-LSR+)))
  