Int 6F Fn 0400  - Hp Vectra Ex-bios - "f_io_ctrl Sf_lock" - Reserve Sub-a  [b]

   AX = 0400h
   BP = driver ID (see #3412)
   DH,DL = major,minor address (optional)

Return: AH = status (see #3415)
   BP,DS destroyed
Desc:  reserve specified sub-addresses on an already-allocated driver for
     exclusive access

Note:  this function is documented as present but unsupported in the drivers
     V_LTABLET, V_LPOINTER, and V_LTOUCH

See Also: AX=0200h"HP Vectra",AX=0402h"SF_UNLOCK"