INT 2F - EXTENDED MEMORY SPECIFICATION (XMS) - GET DRIVER ADDRESS
AX = 4310h
Return: ES:BX -> driver entry point
Note:   HIMEM.SYS v2.77 chains to previous handler if AH is not 00h or 10h

Perform a FAR call to the driver entry point with AH set to the function code
AH      function
00h  Get XMS version number
Return: AX = XMS version (in BCD, AH=major, AL=minor)
BX = internal revision number
DX = 0001h if HMA (1M to 1M + 64K) exists
0000h if HMA does not exist
01h  Request High Memory Area (1M to 1M + 64K)
DX = memory in bytes (for TSR or device drivers)
FFFFh if application program
Return: AX = 0001h success
= 0000h failure
BL = error code (80h,81h,90h,91h,92h) (see below)
02h  Release High Memory Area
Return: AX = 0001h success
= 0000h failure
BL = error code (80h,81h,90h,93h) (see below)
03h  Global enable A20, for using the HMA
Return: AX = 0001h success
= 0000h failure
BL = error code (80h,81h,82h) (see below)
04h  Global disable A20
Return: AX = 0001h success
= 0000h failure
BL = error code (80h,81h,82h,94h) (see below)
05h  Local enable A20, for direct access to extended memory
Return: AX = 0001h success
= 0000h failure
BL = error code (80h,81h,82h) (see below)
06h  Local disable A20
Return: AX = 0001h success
= 0000h failure
BL = error code (80h,81h,82h,94h) (see below)
07h  Query A20 state
Return: AX = 0001h enabled
= 0000h disabled
BL = error code (00h,80h,81h) (see below)
08h  Query free extended memory, not counting HMA
BL = 00h (some implementations leave BL unchanged on success)
Return: AX = size of largest extended memory block in K
DX = total extended memory in K
BL = error code (00h,80h,81h,A0h) (see below)
09h  Allocate extended memory block
DX = Kbytes needed
Return: AX = 0001h success
DX = handle for memory block
= 0000h failure
BL = error code (80h,81h,A0h) (see below)
0Ah  Free extended memory block
DX = handle of block to free
Return: AX = 0001h success
= 0000h failure
BL = error code (80h,81h,A2h,ABh) (see below)
0Bh  Move extended memory block
DS:SI -> EMM structure (see below)
Note: if either handle is 0000h, the corresponding offset is
considered to be an absolute segment:offset address in
directly addressable memory
Return: AX = 0001h success
= 0000h failure
BL = error code (80h-82h,A3h-A9h) (see below)
0Ch  Lock extended memory block
DX = handle of block to lock
Return: AX = 0001h success
DX:BX = 32-bit linear address of locked block
= 0000h failure
BL = error code (80h,81h,A2h,ACh,ADh) (see below)
0Dh  Unlock extended memory block
DX = handle of block to unlock
Return: AX = 0001h success
= 0000h failure
BL = error code (80h,81h,A2h,AAh) (see below)
0Eh  Get handle information
DX = handle for which to get info
Return: AX = 0001h success
BH = block's lock count
BL = number of free handles left
DX = block size in K
= 0000h failure
BL = error code (80h,81h,A2h) (see below)
0Fh  Reallocate extended memory block
DX = handle of block
BX = new size of block in K
Return: AX = 0001h success
= 0000h failure
BL = error code (80h,81h,A0h-A2h,ABh) (see below)
10h  Request upper memory block (nonEMS memory above 640K)
DX = size of block in paragraphs
Return: AX = 0001h success
BX = segment address of UMB
DX = actual size of block
= 0000h failure
BL = error code (80h,B0h,B1h) (see below)
DX = largest available block
11h  Release upper memory block
DX = segment address of UMB to release
Return: AX = 0001h success
= 0000h failure
BL = error code (80h,B2h) (see below)
12h  (XMS v3.0) Reallocate upper memory block
DX = segment address of UMB to resize
BX = new size of block in paragraphs
Return: AX = 0001h success
= 0000h failure
BL = error code (80h,B0h,B2h) (see below)
34h  (QEMM 5.11 only, undocumented) ???
44h  (QEMM 5.11 only, undocumented) ???
88h  (XMS v3.0) Query free extended memory
Return: EAX = largest block of extended memory, in K
BL = status
00h success
80h not implemented (i.e. on a 286 system)
81h VDISK detected
A0h all extended memory allocated
ECX = physical address of highest byte of memory
(valid even on error codes 81h and A0h)
EDX = total Kbytes of extended memory (0 if status A0h)
89h  (XMS v3.0) Allocate any extended memory
EDX = Kbytes needed
Return: AX = 0001h success
DX = handle for allocated block (free with AH=0Ah)
= 0000h failure
BL = status (80h,81h,A0h,A1h,A2h) (see below)
8Eh  (XMS v3.0) Get extended EMB handle information
DX = handle
Return: AX = 0001h success
BH = block's lock count
CX = number of free handles left
EDX = block size in K
= 0000h failure
BL = status (80h,81h,A2h) (see below)
8Fh  (XMS v3.0) Reallocate any extended memory block
DX = unlocked handle
EBX = new size in K
Return: AX = 0001h success
= 0000h failure
BL = status (80h,81h,A0h-A2h,ABh) (see below)
Notes:  HIMEM.SYS requires at least 256 bytes free stack space
the XMS driver need not implement functions 10h through 12h to be
considered compliant with the standard

Format of EMM structure:
Offset  Size    Description
00h    DWORD   number of bytes to move (must be even)
04h    WORD    source handle
06h    DWORD   offset into source block
0Ah    WORD    destination handle
0Ch    DWORD   offset into destination block
Notes:  if source and destination overlap, only forward moves (source base
less than destination base) are guaranteed to work properly
if either handle is zero, the corresponding offset is interpreted
as a real-mode address referring to memory directly addressable
by the processor

Error codes returned in BL:
00h successful
80h function not implemented
81h Vdisk was detected
82h an A20 error occurred
8Eh a general driver error
8Fh unrecoverable driver error
90h HMA does not exist
91h HMA is already in use
92h DX is less than the /HMAMIN= parameter
93h HMA is not allocated
94h A20 line still enabled
A0h all extended memory is allocated
A1h all available extended memory handles are allocated
A2h invalid handle
A3h source handle is invalid
A4h source offset is invalid
A5h destination handle is invalid
A6h destination offset is invalid
A7h length is invalid
A8h move has an invalid overlap
A9h parity error occurred
AAh block is not locked
ABh block is locked
ACh block lock count overflowed
ADh lock failed
B0h only a smaller UMB is available
B1h no UMB's are available
B2h UMB segment number is invalid

See also: 2F4300

2F4310 - EXTENDED MEMORY SPECIFICATION (XMS) - GET DRIVER ADDRESS