1 eXtended Memory Specification (XMS), ver 3.0
\r
7 Copyright (c) 1988, Microsoft Corporation, Lotus Development
\r
8 Corporation, Intel Corporation, and AST Research, Inc.
\r
10 Microsoft Corporation
\r
21 This specification was jointly developed by Microsoft Corporation,
\r
22 Lotus Development Corporation, Intel Corporation,and AST Research,
\r
23 Inc. Although it has been released into the public domain and is not
\r
24 confidential or proprietary, the specification is still the copyright
\r
25 and property of Microsoft Corporation, Lotus Development Corporation,
\r
26 Intel Corporation, and AST Research, Inc.
\r
28 Disclaimer of Warranty
\r
30 MICROSOFT CORPORATION, LOTUS DEVELOPMENT CORPORATION, INTEL
\r
31 CORPORATION, AND AST RESEARCH, INC., EXCLUDE ANY AND ALL IMPLIED
\r
32 WARRANTIES, INCLUDING WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
\r
33 PARTICULAR PURPOSE. NEITHER MICROSOFT NOR LOTUS NOR INTEL NOR AST
\r
34 RESEARCH MAKE ANY WARRANTY OF REPRESENTATION, EITHER EXPRESS OR
\r
35 IMPLIED, WITH RESPECT TO THIS SPECIFICATION, ITS QUALITY,
\r
36 PERFORMANCE, MERCHANTABILITY, OR FITNESS FOR A PARTICULAR PURPOSE.
\r
37 NEITHER MICROSOFT NOR LOTUS NOR INTEL NOR AST RESEARCH SHALL HAVE ANY
\r
38 LIABILITY FOR SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES ARISING
\r
39 OUT OF OR RESULTING FROM THE USE OR MODIFICATION OF THIS
\r
42 This specification uses the following trademarks:
\r
44 Intel is a registered trademark of Intel Corporation, Microsoft is a
\r
45 registered trademark of Microsoft Corporation, Lotus is a registered
\r
46 trademark of Lotus Development Corporation, and AST is a registered
\r
47 trademark of AST Research, Inc.
\r
51 Extended Memory Specification
\r
53 The purpose of this document is to define the Extended Memory Specification (XMS) version 3.00 for MS-DOS. XMS allows DOS programs to utilize additional memory found in Intel's 80286 and 80386 based machines in a consistent, machine independent manner. With some restrictions, XMS adds almost 64K to the 640K which DOS programs can access directly. Depending on available hardware, XMS may provide even more memory to DOS programs. XMS also provides DOS programs with a standard method of storing data in extended memory.
\r
55 To be considered fully XMS 3.0 compliant, all calls except those associated with UMB support must be implemented. UMB functions 10h, 11h and 12h are optional for XMS 3.0 and may return the Function Not Implemented error code, 80h.
\r
61 Memory in 80286 and 80386 based machines which is located above the 1MB address boundary.
\r
63 High Memory Area (HMA):
\r
64 The first 64K of extended memory. The High Memory Area is unique because code can be executed in it while in real mode. The HMA officially starts at FFFF:10h and ends at FFFF:FFFFh making it 64K-16 bytes in length.
\r
66 Upper Memory Blocks (UMBs):
\r
67 Blocks of memory available on some 80x86 based machines which are located between DOS's 640K limit and the 1MB address boundary. The number, size, and location of these blocks vary widely depending upon the types of hardware adapter cards installed in the machine.
\r
69 Extended Memory Blocks (EMBs):
\r
70 Blocks of extended memory located above the HMA which can only be used for data storage.
\r
73 The 21st address line of 80x86 CPUs. Enabling the A20 line allows access to the HMA.
\r
76 An Extended Memory Manager. A DOS device driver which implements XMS. XMMs are machine specific but allow programs to use extended memory in a machine-independent manner.
\r
79 The Extended Memory Manager currently being distributed by Microsoft.
\r
95 | Possible Extended Memory Block |
\r
105 | Other EMBs could exist above 1088K (1MB+64K) |
\r
111 | The High Memory Area |
\r
122 | Possible Upper Memory Block |
\r
129 | Other UMBs could exist between 640K and 1MB |
\r
136 | Conventional or DOS Memory |
\r
144 DRIVER INSTALLATION:
\r
145 --------------------
\r
147 An XMS driver is installed by including a DEVICE= statement in the
\r
148 machine's CONFIG.SYS file. It must be installed prior to any other
\r
149 devices or TSRs which use it. An optional parameter after the driver's
\r
150 name (suggested name "/HMAMIN=") indicates the minimum amount of space in
\r
151 the HMA a program can use. Programs which use less than the minimum will
\r
152 not be placed in the HMA. See "Prioritizing HMA Usage" below for more
\r
153 information. A second optional parameter (suggested name "/NUMHANDLES=")
\r
154 allows users to specify the maximum number of extended memory blocks which
\r
155 may be allocated at any time.
\r
157 NOTE: XMS requires DOS 3.00 or above.
\r
160 THE PROGRAMMING API:
\r
161 --------------------
\r
163 The XMS API Functions are accessed via the XMS driver's Control Function.
\r
164 The address of the Control Function is determined via INT 2Fh. First, a
\r
165 program should determine if an XMS driver is installed. Next, it should
\r
166 retrieve the address of the driver's Control Function. It can then use any
\r
167 of the available XMS functions. The functions are divided into several
\r
170 1. Driver Information Functions (0h)
\r
171 2. HMA Management Functions (1h-2h)
\r
172 3. A20 Management Functions (3h-7h)
\r
173 4. Extended Memory Management Functions (8h-Fh)
\r
174 5. Upper Memory Management Functions (10h-11h)
\r
177 DETERMINING IF AN XMS DRIVER IS INSTALLED:
\r
178 ------------------------------------------
\r
180 The recommended way of determining if an XMS driver is installed is to
\r
181 set AH=43h and AL=00h and then execute INT 2Fh. If an XMS driver is available,
\r
182 80h will be returned in AL.
\r
185 ; Is an XMS driver installed?
\r
192 CALLING THE API FUNCTIONS:
\r
193 --------------------------
\r
195 Programs can execute INT 2Fh with AH=43h and AL=10h to obtain the address
\r
196 of the driver's control function. The address is returned in ES:BX. This
\r
197 function is called to access all of the XMS functions. It should be called
\r
198 with AH set to the number of the API function requested. The API function
\r
199 will put a success code of 0001h or 0000h in AX. If the function succeeded
\r
200 (AX=0001h), additional information may be passed back in BX and DX. If the
\r
201 function failed (AX=0000h), an error code may be returned in BL. Valid
\r
202 error codes have their high bit set. Developers should keep in mind that
\r
203 some of the XMS API functions may not be implemented by all drivers and will
\r
204 return failure in all cases.
\r
207 ; Get the address of the driver's control function
\r
210 mov word ptr [XMSControl],bx ; XMSControl is a DWORD
\r
211 mov word ptr [XMSControl+2],es
\r
213 ; Get the XMS driver's version number
\r
215 call [XMSControl] ; Get XMS Version Number
\r
217 NOTE: Programs should make sure that at least 256 bytes of stack space
\r
218 is available before calling XMS API functions.
\r
221 API FUNCTION DESCRIPTIONS:
\r
222 --------------------------
\r
224 The following XMS API functions are available:
\r
226 0h) Get XMS Version Number
\r
227 1h) Request High Memory Area
\r
228 2h) Release High Memory Area
\r
229 3h) Global Enable A20
\r
230 4h) Global Disable A20
\r
231 5h) Local Enable A20
\r
232 6h) Local Disable A20
\r
234 8h) Query Free Extended Memory
\r
235 9h) Allocate Extended Memory Block
\r
236 Ah) Free Extended Memory Block
\r
237 Bh) Move Extended Memory Block
\r
238 Ch) Lock Extended Memory Block
\r
239 Dh) Unlock Extended Memory Block
\r
240 Eh) Get Handle Information
\r
241 Fh) Reallocate Extended Memory Block
\r
242 10h) Request Upper Memory Block
\r
243 11h) Release Upper Memory Block
\r
244 12h) Realloc Upper Memory Block
\r
245 88h) Query any Free Extended Memory
\r
246 89h) Allocate any Extended Memory Block
\r
247 8Eh) Get Extended EMB Handle
\r
248 8Fh) Realloc any Extended Memory
\r
250 Each is described below.
\r
253 Get XMS Version Number (Function 00h):
\r
254 --------------------------------------
\r
257 RETS: AX = XMS version number
\r
258 BX = Driver internal revision number
\r
259 DX = 0001h if the HMA exists, 0000h otherwise
\r
262 This function returns with AX equal to a 16-bit BCD number representing
\r
263 the revision of the DOS Extended Memory Specification which the driver
\r
264 implements (e.g. AX=0235h would mean that the driver implemented XMS version
\r
265 2.35). BX is set equal to the driver's internal revision number mainly for
\r
266 debugging purposes. DX indicates the existence of the HMA (not its
\r
267 availability) and is intended mainly for installation programs.
\r
269 NOTE: This document defines version 3.00 of the specification.
\r
272 Request High Memory Area (Function 01h):
\r
273 ----------------------------------------
\r
276 If the caller is a TSR or device driver,
\r
277 DX = Space needed in the HMA by the caller in bytes
\r
278 If the caller is an application program,
\r
280 RETS: AX = 0001h if the HMA is assigned to the caller, 0000h otherwise
\r
281 ERRS: BL = 80h if the function is not implemented
\r
282 BL = 81h if a VDISK device is detected
\r
283 BL = 90h if the HMA does not exist
\r
284 BL = 91h if the HMA is already in use
\r
285 BL = 92h if DX is less than the /HMAMIN= parameter
\r
287 This function attempts to reserve the 64K-16 byte high memory area for
\r
288 the caller. If the HMA is currently unused, the caller's size parameter is
\r
289 compared to the /HMAMIN= parameter on the driver's command line. If the
\r
290 value passed by the caller is greater than or equal to the amount specified
\r
291 by the driver's parameter, the request succeeds. This provides the ability
\r
292 to ensure that programs which use the HMA efficiently have priority over
\r
293 those which do not.
\r
295 NOTE: See the sections "Prioritizing HMA Usage" and "High Memory Area
\r
296 Restrictions" below for more information.
\r
299 Release High Memory Area (Function 02h):
\r
300 ----------------------------------------
\r
303 RETS: AX = 0001h if the HMA is successfully released, 0000h otherwise
\r
304 ERRS: BL = 80h if the function is not implemented
\r
305 BL = 81h if a VDISK device is detected
\r
306 BL = 90h if the HMA does not exist
\r
307 BL = 93h if the HMA was not allocated
\r
309 This function releases the high memory area and allows other programs to
\r
310 use it. Programs which allocate the HMA must release it before exiting.
\r
311 When the HMA has been released, any code or data stored in it becomes invalid
\r
312 and should not be accessed.
\r
315 Global Enable A20 (Function 03h):
\r
316 ---------------------------------
\r
319 RETS: AX = 0001h if the A20 line is enabled, 0000h otherwise
\r
320 ERRS: BL = 80h if the function is not implemented
\r
321 BL = 81h if a VDISK device is detected
\r
322 BL = 82h if an A20 error occurs
\r
324 This function attempts to enable the A20 line. It should only be used
\r
325 by programs which have control of the HMA. The A20 line should be turned
\r
326 off via Function 04h (Global Disable A20) before a program releases control
\r
329 NOTE: On many machines, toggling the A20 line is a relatively slow
\r
333 Global Disable A20 (Function 04h):
\r
334 ----------------------------------
\r
337 RETS: AX = 0001h if the A20 line is disabled, 0000h otherwise
\r
338 ERRS: BL = 80h if the function is not implemented
\r
339 BL = 81h if a VDISK device is detected
\r
340 BL = 82h if an A20 error occurs
\r
341 BL = 94h if the A20 line is still enabled
\r
343 This function attempts to disable the A20 line. It should only be used
\r
344 by programs which have control of the HMA. The A20 line should be disabled
\r
345 before a program releases control of the system.
\r
347 NOTE: On many machines, toggling the A20 line is a relatively slow
\r
351 Local Enable A20 (Function 05h):
\r
352 --------------------------------
\r
355 RETS: AX = 0001h if the A20 line is enabled, 0000h otherwise
\r
356 ERRS: BL = 80h if the function is not implemented
\r
357 BL = 81h if a VDISK device is detected
\r
358 BL = 82h if an A20 error occurs
\r
360 This function attempts to enable the A20 line. It should only be used
\r
361 by programs which need direct access to extended memory. Programs which use
\r
362 this function should call Function 06h (Local Disable A20) before releasing
\r
363 control of the system.
\r
365 NOTE: On many machines, toggling the A20 line is a relatively slow
\r
369 Local Disable A20 (Function 06h):
\r
370 ---------------------------------
\r
373 RETS: AX = 0001h if the function succeeds, 0000h otherwise
\r
374 ERRS: BL = 80h if the function is not implemented
\r
375 BL = 81h if a VDISK device is detected
\r
376 BL = 82h if an A20 error occurs
\r
377 BL = 94h if the A20 line is still enabled
\r
379 This function cancels a previous call to Function 05h (Local Enable
\r
380 A20). It should only be used by programs which need direct access to
\r
381 extended memory. Previous calls to Function 05h must be canceled before
\r
382 releasing control of the system.
\r
384 NOTE: On many machines, toggling the A20 line is a relatively slow
\r
388 Query A20 (Function 07h):
\r
389 -------------------------
\r
392 RETS: AX = 0001h if the A20 line is physically enabled, 0000h otherwise
\r
393 ERRS: BL = 00h if the function succeeds
\r
394 BL = 80h if the function is not implemented
\r
395 BL = 81h if a VDISK device is detected
\r
397 This function checks to see if the A20 line is physically enabled. It
\r
398 does this in a hardware independent manner by seeing if "memory wrap" occurs.
\r
401 Query Free Extended Memory (Function 08h):
\r
402 ------------------------------------------
\r
405 RETS: AX = Size of the largest free extended memory block in K-bytes
\r
406 DX = Total amount of free extended memory in K-bytes
\r
407 ERRS: BL = 80h if the function is not implemented
\r
408 BL = 81h if a VDISK device is detected
\r
409 BL = A0h if all extended memory is allocated
\r
411 This function returns the size of the largest available extended memory
\r
412 block in the system.
\r
414 NOTE: The 64K HMA is not included in the returned value even if it is
\r
418 Allocate Extended Memory Block (Function 09h):
\r
419 ----------------------------------------------
\r
422 DX = Amount of extended memory being requested in K-bytes
\r
423 RETS: AX = 0001h if the block is allocated, 0000h otherwise
\r
424 DX = 16-bit handle to the allocated block
\r
425 ERRS: BL = 80h if the function is not implemented
\r
426 BL = 81h if a VDISK device is detected
\r
427 BL = A0h if all available extended memory is allocated
\r
428 BL = A1h if all available extended memory handles are in use
\r
430 This function attempts to allocate a block of the given size out of the
\r
431 pool of free extended memory. If a block is available, it is reserved
\r
432 for the caller and a 16-bit handle to that block is returned. The handle
\r
433 should be used in all subsequent extended memory calls. If no memory was
\r
434 allocated, the returned handle is null.
\r
436 NOTE: Extended memory handles are scarce resources. Programs should
\r
437 try to allocate as few as possible at any one time. When all
\r
438 of a driver's handles are in use, any free extended memory is
\r
443 Free Extended Memory Block (Function 0Ah):
\r
444 ------------------------------------------
\r
447 DX = Handle to the allocated block which should be freed
\r
448 RETS: AX = 0001h if the block is successfully freed, 0000h otherwise
\r
449 ERRS: BL = 80h if the function is not implemented
\r
450 BL = 81h if a VDISK device is detected
\r
451 BL = A2h if the handle is invalid
\r
452 BL = ABh if the handle is locked
\r
454 This function frees a block of extended memory which was previously
\r
455 allocated using Function 09h (Allocate Extended Memory Block). Programs
\r
456 which allocate extended memory should free their memory blocks before
\r
457 exiting. When an extended memory buffer is freed, its handle and all data
\r
458 stored in it become invalid and should not be accessed.
\r
461 Move Extended Memory Block (Function 0Bh):
\r
462 ------------------------------------------
\r
465 DS:SI = Pointer to an Extended Memory Move Structure (see below)
\r
466 RETS: AX = 0001h if the move is successful, 0000h otherwise
\r
467 ERRS: BL = 80h if the function is not implemented
\r
468 BL = 81h if a VDISK device is detected
\r
469 BL = 82h if an A20 error occurs
\r
470 BL = A3h if the SourceHandle is invalid
\r
471 BL = A4h if the SourceOffset is invalid
\r
472 BL = A5h if the DestHandle is invalid
\r
473 BL = A6h if the DestOffset is invalid
\r
474 BL = A7h if the Length is invalid
\r
475 BL = A8h if the move has an invalid overlap
\r
476 BL = A9h if a parity error occurs
\r
478 Extended Memory Move Structure Definition:
\r
480 ExtMemMoveStruct struc
\r
481 Length dd ? ; 32-bit number of bytes to transfer
\r
482 SourceHandle dw ? ; Handle of source block
\r
483 SourceOffset dd ? ; 32-bit offset into source
\r
484 DestHandle dw ? ; Handle of destination block
\r
485 DestOffset dd ? ; 32-bit offset into destination block
\r
486 ExtMemMoveStruct ends
\r
488 This function attempts to transfer a block of data from one location to
\r
489 another. It is primarily intended for moving blocks of data between
\r
490 conventional memory and extended memory, however it can be used for moving
\r
491 blocks within conventional memory and within extended memory.
\r
493 NOTE: If SourceHandle is set to 0000h, the SourceOffset is interpreted
\r
494 as a standard segment:offset pair which refers to memory that is
\r
495 directly accessible by the processor. The segment:offset pair
\r
496 is stored in Intel DWORD notation. The same is true for DestHandle
\r
499 SourceHandle and DestHandle do not have to refer to locked memory
\r
502 Length must be even. Although not required, WORD-aligned moves
\r
503 can be significantly faster on most machines. DWORD aligned move
\r
504 can be even faster on 80386 machines.
\r
506 If the source and destination blocks overlap, only forward moves
\r
507 (i.e. where the source base is less than the destination base) are
\r
508 guaranteed to work properly.
\r
510 Programs should not enable the A20 line before calling this
\r
511 function. The state of the A20 line is preserved.
\r
513 This function is guaranteed to provide a reasonable number of
\r
514 interrupt windows during long transfers.
\r
517 Lock Extended Memory Block (Function 0Ch):
\r
518 ------------------------------------------
\r
521 DX = Extended memory block handle to lock
\r
522 RETS: AX = 0001h if the block is locked, 0000h otherwise
\r
523 DX:BX = 32-bit physical address of the locked block
\r
524 ERRS: BL = 80h if the function is not implemented
\r
525 BL = 81h if a VDISK device is detected
\r
526 BL = A2h if the handle is invalid
\r
527 BL = ACh if the block's lock count overflows
\r
528 BL = ADh if the lock fails
\r
530 This function locks an extended memory block and returns its base
\r
531 address as a 32-bit physical address. Locked memory blocks are guaranteed not
\r
532 to move. The 32-bit pointer is only valid while the block is locked.
\r
533 Locked blocks should be unlocked as soon as possible.
\r
535 NOTE: A block does not have to be locked before using Function 0Bh (Move
\r
536 Extended Memory Block).
\r
538 "Lock counts" are maintained for EMBs.
\r
542 Unlock Extended Memory Block (Function 0Dh):
\r
543 --------------------------------------------
\r
546 DX = Extended memory block handle to unlock
\r
547 RETS: AX = 0001h if the block is unlocked, 0000h otherwise
\r
548 ERRS: BL = 80h if the function is not implemented
\r
549 BL = 81h if a VDISK device is detected
\r
550 BL = A2h if the handle is invalid
\r
551 BL = AAh if the block is not locked
\r
553 This function unlocks a locked extended memory block. Any 32-bit
\r
554 pointers into the block become invalid and should no longer be used.
\r
557 Get EMB Handle Information (Function 0Eh):
\r
558 ------------------------------------------
\r
561 DX = Extended memory block handle
\r
562 RETS: AX = 0001h if the block's information is found, 0000h otherwise
\r
563 BH = The block's lock count
\r
564 BL = Number of free EMB handles in the system
\r
565 DX = The block's length in K-bytes
\r
566 ERRS: BL = 80h if the function is not implemented
\r
567 BL = 81h if a VDISK device is detected
\r
568 BL = A2h if the handle is invalid
\r
570 This function returns additional information about an extended memory
\r
571 block to the caller.
\r
573 NOTE: To get the block's base address, use Function 0Ch (Lock Extended
\r
577 Reallocate Extended Memory Block (Function 0Fh):
\r
578 ------------------------------------------------
\r
581 BX = New size for the extended memory block in K-bytes
\r
582 DX = Unlocked extended memory block handle to reallocate
\r
583 RETS: AX = 0001h if the block is reallocated, 0000h otherwise
\r
584 ERRS: BL = 80h if the function is not implemented
\r
585 BL = 81h if a VDISK device is detected
\r
586 BL = A0h if all available extended memory is allocated
\r
587 BL = A1h if all available extended memory handles are in use
\r
588 BL = A2h if the handle is invalid
\r
589 BL = ABh if the block is locked
\r
591 This function attempts to reallocate an unlocked extended memory block
\r
592 so that it becomes the newly specified size. If the new size is smaller
\r
593 than the old block's size, all data at the upper end of the old block is
\r
597 Request Upper Memory Block (Function 10h):
\r
598 ------------------------------------------
\r
601 DX = Size of requested memory block in paragraphs
\r
602 RETS: AX = 0001h if the request is granted, 0000h otherwise
\r
603 BX = Segment number of the upper memory block
\r
604 If the request is granted,
\r
605 DX = Actual size of the allocated block in paragraphs
\r
607 DX = Size of the largest available UMB in paragraphs
\r
608 ERRS: BL = 80h if the function is not implemented
\r
609 BL = B0h if a smaller UMB is available
\r
610 BL = B1h if no UMBs are available
\r
612 This function attempts to allocate an upper memory block to the caller.
\r
613 If the function fails, the size of the largest free UMB is returned in DX.
\r
615 NOTE: By definition UMBs are located below the 1MB address boundary.
\r
616 The A20 Line does not need to be enabled before accessing an
\r
619 UMBs are paragraph aligned.
\r
621 To determine the size of the largest available UMB, attempt to
\r
622 allocate one with a size of FFFFh.
\r
624 UMBs are unaffected by EMS calls.
\r
627 Release Upper Memory Block (Function 11h):
\r
628 ------------------------------------------
\r
631 DX = Segment number of the upper memory block
\r
632 RETS: AX = 0001h if the block was released, 0000h otherwise
\r
633 ERRS: BL = 80h if the function is not implemented
\r
634 BL = B2h if the UMB segment number is invalid
\r
636 This function frees a previously allocated upper memory block. When an
\r
637 UMB has been released, any code or data stored in it becomes invalid and
\r
638 should not be accessed.
\r
643 Reallocate Upper Memory Block (Function 12h)
\r
647 BX = New size for UMB in paragraphs
\r
648 DX = Segment number of the UMB to reallocate
\r
650 AX = 1 if the block was reallocated, 0 otherwise
\r
652 BL = 80h if the function is not implemented
\r
653 BL = B0h if no UMB large enough to satisfy the request is available.
\r
654 In this event, DX is returned with the size of the largest UMB that is available.
\r
655 BL = B2h if the UMB segment number is invalid
\r
657 This function attempts to reallocate an Upper Memory Block to a newly specified size. If the new size is smaller than the old block's size, all data at the upper end of the block is lost.
\r
661 Super Extended Memory Support
\r
663 These changes are intended to provide support for extended memory pools up to 4 Gb in size. The current XMS API, since it uses 16-bit values to specify block sizes in Kb, is limited to 64 Mb maximum block size. Future machines are expected to support memory above 64 MB.
\r
665 This support is implemented in the form of extensions to existing functions, rather than entirely new entry points, to allow for more efficient implementations.
\r
667 Programs should generally use the existing functions, instead of these extended ones, unless they have an explicit need to deal with memory above 64 Mb.
\r
670 Query Any Free Extended Memory (Function 88h)
\r
675 EAX = Size of largest free extended memory block in Kb.
\r
676 BL = 0 if no error occurs, otherwise it takes an error code.
\r
677 ECX = Highest ending address of any memory block.
\r
678 EDX = Total amount of free memory in Kb.
\r
680 BL = 80h if the function is not implemented.
\r
681 BL = 81h if a VDISK device is detected.
\r
682 BL = A0h if all extended memory is allocated.
\r
684 This function uses 32-bit values to return the size of available memory, thus allowing returns up to 4GByte. Additionally, it returns the highest known physical memory address, that is, the physical address of the last byte of memory. There may be discontinuities in the memory map below this address.
\r
686 The memory pool reported on is the same as that reported on by the existing Query Free Extended Memory function. If the highest memory address is not more than 64 Mb, then these two functions will return the same results.
\r
688 Because of its reliance on 32-bit registers, this function is only available on 80386 and higher processors. XMS drivers on 80286 machines should return error code 80h if this function is called.
\r
690 If error code 81h is returned, the value in ECX will still be valid. If error code A0h is returned, EAX and EDX will be 0, and ECX will still be valid.
\r
693 Allocate Any Extended Memory (Function 89h)
\r
697 EDX = Amount of extended memory requested, in Kb.
\r
699 AX = 1 if the block is allocated, 0 if not
\r
700 DX = Handle to allocated block.
\r
702 BL = 80h if the function is not implemented.
\r
703 BL = 81h if a VDISK device is detected.
\r
704 BL = A0h if all available extended memory is allocated.
\r
705 BL = A1h if all available extended memory handles are in use.
\r
707 This function is similar to the existing Allocate Extended Memory, except that it uses a 32-bit instead of a 16-bit value to specify the amount of memory requested. It allocates from the same memory and handle pool as the current function. Since it requires a 32-bit register, this function can be supported only on 80386 and higher processors, and XMS drivers on 80286 machines should return error code 80h.
\r
710 Get Extended EMB Handle Information (Function 8Eh)
\r
714 DX = Extended memory block handle.
\r
716 AX = 1 if the block's information is found, 0 if not
\r
717 BH = Block lock count
\r
718 CX = Number of free EMB handles in the system
\r
719 EDX = Block's length in Kb.
\r
721 BL = 80h if the function is not implemented.
\r
722 BL = 81h if a VDISK device is detected.
\r
723 BL = A2h if the handle is invalid.
\r
725 This function is similar to the Get EMB Handle Information function. Since it uses a 32-bit register to report the block size, it can be used to get information on blocks larger than 64 Mb. It also uses a 16-bit instead of 8-bit register to report the number of free handles, allowing the handle pool to be extended beyond 256 entries.
\r
727 Because of its reliance on a 32-bit register, this function is available on 80386 and higher processors. XMS drivers on 80286 machines should return error code 80h if this function is called.
\r
730 Reallocate Any Extended Memory (Function 8Fh)
\r
734 EBX = New size for extended memory block, in Kb.
\r
735 DX = Unlocked handle for memory block to be resized.
\r
737 AX = 1 if the block is reallocated, 0 if not
\r
739 BL = 80h if the function is not implemented.
\r
740 BL = 81h if a VDISK device is detected.
\r
741 BL = A0h if all available extended memory is allocated.
\r
742 BL = A1h if all available extended memory handles are in use.
\r
743 BL = A2h if the handle is invalid.
\r
744 BL = ABh if the block is locked.
\r
746 This function is similar to the existing Reallocate Extended Memory, except that it uses a 32-bit instead of a 16-bit value to specify the amount of memory requested. It allocates from the same memory and handle pool as the current function. Since it requires a 32-bit register, this function can be supported only on 80386 and higher processors, and XMS drivers on 80286 machines should return error code 80h.
\r
751 PRIORITIZING HMA USAGE:
\r
752 -----------------------
\r
754 For DOS users to receive the maximum benefit from the High Memory Area,
\r
755 programs which use the HMA must store as much of their resident code in it as
\r
756 is possible. It is very important that developers realize that the HMA is
\r
757 allocated as a single unit.
\r
759 For example, a TSR program which grabs the HMA and puts 10K of code into
\r
760 it may prevent a later TSR from putting 62K into the HMA. Obviously, regular
\r
761 DOS programs would have more memory available to them below the 640K line if
\r
762 the 62K TSR was moved into the HMA instead of the 10K one.
\r
764 The first method for dealing with conflicts such as this is to require
\r
765 programs which use the HMA to provide a command line option for disabling
\r
766 this feature. It is crucial that TSRs which do not make full use of the HMA
\r
767 provide such a switch on their own command line (suggested name "/NOHMA").
\r
769 The second method for optimizing HMA usage is through the /HMAMIN=
\r
770 parameter on the XMS device driver line. The number after the parameter
\r
771 is defined to be the minimum amount of HMA space (in K-bytes) used by any
\r
772 driver or TSR. For example, if "DEVICE=HIMEM.SYS /HMAMIN=48" is in a
\r
773 user's CONFIG.SYS file, only programs which request at least 48K would be
\r
774 allowed to allocate the HMA. This number can be adjusted either by
\r
775 installation programs or by the user himself. If this parameter is not
\r
776 specified, the default value of 0 is used causing the HMA to be allocated
\r
777 on a first come, first served basis.
\r
779 Note that this problem does not impact application programs. If the HMA
\r
780 is available when an application program starts, the application is free to
\r
781 use as much or as little of the HMA as it wants. For this reason,
\r
782 applications should pass FFFFh in DX when calling Function 01h.
\r
786 HIGH MEMORY AREA RESTRICTIONS:
\r
787 ------------------------------
\r
789 - Far pointers to data located in the HMA cannot be passed to DOS. DOS
\r
790 normalizes any pointer which is passed into it. This will cause data
\r
791 addresses in the HMA to be invalidated.
\r
793 - Disk I/O directly into the HMA (via DOS, INT 13h, or otherwise) is not
\r
796 - Programs, especially drivers and TSRs, which use the HMA *MUST* use
\r
797 as much of it as possible. If a driver or TSR is unable to use at
\r
798 least 90% of the available HMA (typically ~58K), they must provide
\r
799 a command line switch for overriding HMA usage. This will allow
\r
800 the user to configure his machine for optimum use of the HMA.
\r
802 - Device drivers and TSRs cannot leave the A20 line permanently turned
\r
803 on. Several applications rely on 1MB memory wrap and will overwrite the
\r
804 HMA if the A20 line is left enabled potentially causing a system crash.
\r
806 - Interrupt vectors must not point into the HMA. This is a result of
\r
807 the previous restriction. Note that interrupt vectors can point into
\r
808 any allocated upper memory blocks however.
\r
813 If AX=0000h when a function returns and the high bit of BL is set,
\r
815 BL=80h if the function is not implemented
\r
816 81h if a VDISK device is detected
\r
817 82h if an A20 error occurs
\r
818 8Eh if a general driver error occurs
\r
819 8Fh if an unrecoverable driver error occurs
\r
820 90h if the HMA does not exist
\r
821 91h if the HMA is already in use
\r
822 92h if DX is less than the /HMAMIN= parameter
\r
823 93h if the HMA is not allocated
\r
824 94h if the A20 line is still enabled
\r
825 A0h if all extended memory is allocated
\r
826 A1h if all available extended memory handles are in use
\r
827 A2h if the handle is invalid
\r
828 A3h if the SourceHandle is invalid
\r
829 A4h if the SourceOffset is invalid
\r
830 A5h if the DestHandle is invalid
\r
831 A6h if the DestOffset is invalid
\r
832 A7h if the Length is invalid
\r
833 A8h if the move has an invalid overlap
\r
834 A9h if a parity error occurs
\r
835 AAh if the block is not locked
\r
836 ABh if the block is locked
\r
837 ACh if the block's lock count overflows
\r
838 ADh if the lock fails
\r
839 B0h if a smaller UMB is available
\r
840 B1h if no UMBs are available
\r
841 B2h if the UMB segment number is invalid
\r
844 IMPLEMENTATION NOTES FOR DOS XMS DRIVERS:
\r
845 -----------------------------------------
\r
847 - A DOS XMS driver's control function must begin with code similar to the
\r
850 XMMControl proc far
\r
852 jmp short XCControlEntry ; For "hookability"
\r
853 nop ; NOTE: The jump must be a short
\r
854 nop ; jump to indicate the end of
\r
855 nop ; any hook chainThe nop's
\r
856 ; allow a far jump to be
\r
861 - XMS drivers must preserve all registers except those containing
\r
862 returned values across any function call.
\r
864 - XMS drivers are required to hook INT 15h and watch for calls to
\r
865 functions 87h (Block Move) and 88h (Extended Memory Available). The
\r
866 INT 15h Block Move function must be hooked so that the state of the A20
\r
867 line is preserved across the call. The INT 15h Extended Memory
\r
868 Available function must be hooked to return 0h to protect the HMA.
\r
870 - In order to maintain compatibility with existing device drivers, DOS XMS
\r
871 drivers must not hook INT 15h until the first non-Version Number call
\r
872 to the control function is made.
\r
874 - XMS drivers are required to check for the presence of drivers which
\r
875 use the IBM VDISK allocation scheme. Note that it is not sufficient to
\r
876 check for VDISK users at installation time but at the time when the HMA
\r
877 is first allocated. If a VDISK user is detected, the HMA must not be
\r
878 allocated. Microsoft will publish a standard method for detecting
\r
879 drivers which use the VDISK allocation scheme.
\r
881 - XMS drivers which have a fixed number of extended memory handles (most
\r
882 do) should implement a command line parameter for adjusting that number
\r
883 (suggested name "/NUMHANDLES=")
\r
885 - XMS drivers should make sure that the major DOS version number is
\r
886 greater than or equal to 3 before installing themselves.
\r
888 - UMBs cannot occupy memory addresses that can be banked by EMS 4.0.
\r
889 EMS 4.0 takes precedence over UMBs for physically addressable memory.
\r
891 - All driver functions must be re-entrant. Care should be taken to not
\r
892 leave interrupts disabled for long periods of time.
\r
894 - Allocation of a zero length extended memory buffer is allowed. Programs
\r
895 which hook XMS drivers may need to reserve a handle for private use via
\r
896 this method. Programs which hook an XMS driver should pass all requests
\r
897 for zero length EMBs to the next driver in the chain.
\r
899 - Drivers should control the A20 line via an "enable count." Local En-
\r
900 able only enables the A20 line if the count is zero. It then increments
\r
901 the count. Local Disable only disables A20 if the count is one. It
\r
902 then decrements the count. Global Enable/Disable keeps a flag which
\r
903 indicates the state of A20. They use Local Enable/Disable to actually
\r
906 - Drivers should always check the physical A20 state in the local Enable-Disable calls, to see
\r
907 that the physical state matches the internal count. If the physical state does not match, it should
\r
908 be modified so that it matches the internal count. This avoids problems with applications that
\r
909 modify A20 directly.
\r
912 IMPLEMENTATION OF CODE FOR HOOKING THE XMS DRIVER:
\r
914 In order to support the hooking of the XMS driver by multiple
\r
915 pieces of code, the following code sample should be followed.
\r
916 Use of other methods for hooking the XMS driver will not work
\r
917 in many cases. This method is the official supported one.
\r
919 The basic strategy is:
\r
921 Find the XMS driver header which has the "near jump" dispatch.
\r
923 Patch the near jump to a FAR jump which jumps to my HOOK XMS
\r
928 o This architecture allows the most recent HOOKer to undo his
\r
929 XMS driver hook at any time without having to worry about
\r
930 damaging a "hook chain".
\r
932 o This architecture allows the complete XMS hook chain to be
\r
933 enumerated at any time. There are no "hidden hooks".
\r
935 o This architecture allows the HOOKer to not have to worry
\r
936 about installing an "INT 2F hook" to hook the AH=43h
\r
937 INT 2Fs handled by the XMS driver. The base XMS driver
\r
938 continues to be the only one installed on INT 2Fh AH=43h.
\r
940 This avoids all of the problems of undoing a software
\r
944 ; When I wish to CHAIN to the previous XMS driver, I execute a FAR JMP
\r
945 ; to the address stored in this DWORD.
\r
947 PrevXMSControlAddr dd ?
\r
950 ; The next two data items are needed ONLY if I desire to be able to undo
\r
952 ; PrevXMSControlJmpVal stores the previos XMS dispatch near jump offset
\r
953 ; value that is used to unhook my XMS hook
\r
954 ; PrevXMSControlBase stores the address of the XMS header that I hooked
\r
956 PrevXMSControlBase dd ?
\r
957 PrevXMSControlJmpVal db ?
\r
960 ; This is MY XMS control header.
\r
962 MyXMSControlFunc proc FAR
\r
963 jmp short XMSControlEntry
\r
972 jmp cs:[PrevXMSControlAddr]
\r
974 MyXMSControlFunc endp
\r
979 ; This is the code which installs my hook into the XMS driver.
\r
982 ; See if there is an XMS driver to hook
\r
987 jne NoXMSDrvrToHookError
\r
989 ; Get the current XMS driver Control address
\r
994 mov word ptr [PrevXMSControlAddr+2],es
\r
995 mov word ptr [PrevXMSControlBase+2],es
\r
996 mov word ptr [PrevXMSControlBase],bx
\r
997 mov cx,word ptr es:[bx]
\r
998 cmp cl,0EBh ; Near JUMP
\r
1000 cmp cl,0EAh ; Far JUMP
\r
1001 jne XMSDrvrChainMessedUpError
\r
1003 mov si,word ptr es:[bx+1] ; Offset of jump
\r
1004 mov es,word ptr es:[bx+1+2] ; Seg of jump
\r
1006 jmp short NextXMSHeader
\r
1009 cmp word ptr es:[bx+2],9090h ; Two NOPs?
\r
1010 jne XMSDrvrChainMessedUpError ; No
\r
1011 cmp byte ptr es:[bx+4],90h ; Total of 3 NOPs?
\r
1012 jne XMSDrvrChainMessedUpError ; No
\r
1013 mov di,bx ; Save pointer to header
\r
1015 mov al,ch ; jmp addr of near jump
\r
1016 mov [PrevXMSControlJmpVal],al
\r
1017 add ax,2 ; NEAR JMP is 2 byte instruction
\r
1018 add bx,ax ; Target of jump
\r
1019 mov word ptr [PrevXMSControlAddr],bx
\r
1021 ; Now INSTALL my XMS HOOK
\r
1023 cli ; Disable INTs in case someone calls
\r
1024 ; XMS at interrupt time
\r
1025 mov byte ptr es:[di],0EAh ; Far Immed. JUMP instruction
\r
1026 mov word ptr es:[di+1],offset MyXMSControlFunc
\r
1027 mov word ptr es:[di+3],cs
\r
1032 ; Deinstall my XMS hook. This can be done IF AND ONLY IF my XMS header
\r
1033 ; still contains the near jump dispatch
\r
1035 cmp byte ptr [MyXMSControlFunc],0EBh
\r
1036 jne CantDeinstallError
\r
1038 mov ah,[PrevXMSControlJmpVal]
\r
1039 les bx,[PrevXMSControlBase]
\r
1040 cli ; Disable INTs in case someone calls
\r
1041 ; XMS at interrupt time
\r
1042 mov word ptr es:[bx],ax
\r
1043 mov word ptr es:[bx+2],9090h
\r
1044 mov byte ptr es:[bx+4],90h
\r
1048 IMPLEMENTATION NOTES FOR HIMEM.SYS:
\r
1049 -----------------------------------
\r
1051 - HIMEM.SYS currently supports true AT-compatibles, 386 AT machines, IBM
\r
1052 PS/2s, AT&T 6300 Plus systems and Hewlett Packard Vectras.
\r
1054 - If HIMEM finds that it cannot properly control the A20 line or if there
\r
1055 is no extended memory available when HIMEM.SYS is invoked, the driver
\r
1056 does not install itself. HIMEM.SYS displays the message "High Memory
\r
1057 Area Unavailable" when this situation occurs.
\r
1059 - If HIMEM finds that the A20 line is already enabled when it is invoked,
\r
1060 it will NOT change the A20 line's state. The assumption is that whoever
\r
1061 enabled it knew what they were doing. HIMEM.SYS displays the message "A20
\r
1062 Line Permanently Enabled" when this situation occurs.
\r
1064 - HIMEM.SYS is incompatible with IBM's VDISK.SYS driver and other drivers
\r
1065 which use the VDISK scheme for allocating extended memory. However,
\r
1066 HIMEM does attempt to detect these drivers and will not allocate the
\r
1067 HMA if one is found.
\r
1069 - HIMEM.SYS supports the optional "/HMAMIN=" parameter. The valid values
\r
1070 are decimal numbers between 0 and 63.
\r
1072 - By default, HIMEM.SYS has 32 extended memory handles available for use.
\r
1073 This number may be adjusted with the "/NUMHANDLES=" parameter. The
\r
1074 maximum value for this parameter is 128 and the minimum is 0. Each
\r
1075 handle currently requires 6 bytes of resident space.
\r
1078 Copyright (c) 1988, Microsoft Corporation
\r
projects / 16.git / blob