Int 31H Function 0509H
Map Conventional Memory in Memory Block
Aliases linear addresses below the 1 MB boundary onto the linear
addresses of a memory block previously allocated with Int 31H Function 0504H.
AX = 0509H
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 = linear address of conventional memory (must be
if function successful
Carry flag = clear
if function unsuccessful
Carry flag = set
AX = error code
|8001H||unsupported function (Conventional Memory
Mapping Capability not supported)|
|8003H||system integrity (invalid conventional
|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.
- A client may only map conventional memory that it already owns;
i.e. memory which the client previously allocated with Int 31H Function 0100H or by calling DOS's Int
21H Function 48H directly via the translation services.
- 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).
- DPMI hosts that do not implement virtual memory can support this
function by simply copying page table entries. The entries must be
marked as mapped so that the host knows not to free up those physical
pages when the memory block is freed.
- DPMI hosts that provide virtual memory must implement some form of
page aliasing in order to support this function.
- The function can provide a large contiguous memory space without
virtual memory support.
- Implementors of DPMI hosts which do not provide virtual memory are
encouraged to support this function. Without this function,
conventional memory may be inaccessible to a 32-bit nonsegmented
client, because the client may need contiguous linear memory for its
code and data. 32-bit clients can always guarantee that conventional
memory is not wasted with the following strategy:
- Call DOS to allocate any free conventional memory
- If the DPMI host supports virtual memory, call the Mark Real Mode
Region Pageable function (Int 31H Function
0602H) to ensure that the host has not locked down conventional
- If the host does not support virtual memory but supports the Map
Conventional Memory function (Int 31H Function
0509H), allocate a memory block with uncommitted pages, then use
Function 0509H to make the physical memory
allocated below 640 KB addressable in the memory block, and therefore
useable by the 32-bit application program.