Int 31H Function 0508H
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 Function 0504H.
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
if function successful
Carry flag = clear
if function unsuccessful
Carry flag = set
AX = error code
Capability not supported)
|8001H||unsupported function (Device Mapping|
|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)|
- 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.
- 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.
- 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.
- 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 Function 0506H).
- This function 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.
- Unlike Int 31H Function 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.
- 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
- 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.
- 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