Map Device in Memory Block

Maps the physical addresses assigned to a device onto the
linear addresses of a memory block previously allocated with
Int 31H Fn 0504H.

Call With:

   AX     = 0508H
   ESI    = memory block handle
   EBX    = offset within memory block of page(s) to be
           mapped (must be page-aligned)
   ECX    = number of pages to map
   EDX    = physical address of device (must be
           page-aligned)

Returns:

   if function successful
   Carry flag= clear

   if function unsuccessful
   Carry flag= set
   AX     = error code
           8001H   unsupported function (Device Mapping
                   Capability not supported)
           8003H   system integrity (invalid device address)
           8023H   invalid handle (in ESI)
           8025H   invalid linear address (specified range
                   is not within specified block or EBX/EDX
                   is not page-aligned)

Notes:

o  16-bit DPMI hosts will not support this function.  A
   16-bit client of a 32-bit DPMI 1.0 host can use this
   function.
o  Support of this call by 32-bit DPMI hosts is optional.
   Application programs or DOS Extenders which require this
   call in order to run are not DPMI Compliant.
o  Any committed or mapped pages resided in the linear
   address range that is being mapped into will be
   uncommitted or unmapped automatically by the host.
o  All pages created by this call have the mapped bit (bit
   2) set in the attributes returned by the Get Page
   Attributes function (Int 31H Fn 0506H).
o  This functio
n differs from the Create Physical Address Mapping function (Int 31H
   Function 0800H) in that this function supports mapping of
   physical devices within an existing memory block, rather
   than at an arbitrary linear address.  Use of an existing
   memory block gives 32-bit programs the ability to access
   physical devices with NEAR pointers, which is often
   highly desirable for performance reasons.
o  Unlike Int 31H Fn 0800H, this function allows
   mapping of  addresses below 1 MB that do not lie within
   RAM available for use by programs; e.g. this function can
    be used to map the refresh buffers of IBM-compatible
   display adapters.
o  If the DPMI host is not virtualizing the device,  it must
   disable any memory caching on the mapped pages;  in
   particular, on the 486 or later, the PCD (page cache
   disable) bit must be set in the page table entries.
o  DPMI hosts that do not virtualize physical devices can
   support this function by creating page table entries that
   map the physical device.  The page table entries must be
   marked as mapped so that the host knows not to attempt
   freeing of physical memory for the pages when the memory
   block is freed.
o  DPMI hosts are allowed to support this function for some
   physical devices and not for others, because mapping of
   virtualized devices requires page aliasing in the host -
   a complex task.  DPMI hosts with partial support for this
   function may fail the function call on virtualized
   devices (such as displays), and allow the call on
   non-virtualized devices (such as the Weitek
   coprocessors).  Allowing the client to map  a physical
   device so that it can be accessed with NEAR references,
   for example, may help the client achieve considerably
   better performance.