DOS ain't dead

Hello Everyone,
Sorry if this is an old age problem, searched many threads but unable to find anything related. My work environment is running MS-DOS 7, NASM (Ver 2.10.07) & HDPMI32 (ver 3.17) , having problem with loading a file's content to a buffer above 1MB, i.e
.
.
.
mov AH, 3Fh ;Read from file
mov BX, word [DS:FileHandle] ;File successfully Opened prior to this
mov ECX, 1000h ;Read 4096 Bytes from File
mov EDX, 300000h ;Buffer to store 1000h bytes to.
int 21h
.
.

Compiled Ok but hangs when executed with HDPMI32 loaded or otherwise.

I thought HDPMI32 would somehow intercept int 21h/AH=3F in protected mode and accept 32bit addressing unlike its 16bit counterpart ?
Would appreciate any suggestions, thanks for reading.

NOTE: Also tried other DPMIs to no avail.

> Hello Everyone,
> mov AH, 3Fh ;Read from file
> mov BX, word [DS:FileHandle] ;File successfully Opened prior to this
> mov ECX, 1000h ;Read 4096 Bytes from File
> mov EDX, 300000h ;Buffer to store 1000h bytes to.
> int 21h
>
> I thought HDPMI32 would somehow intercept int 21h/AH=3F in protected mode

Yes, it does. But the address in DS:EDX must point to a valid buffer. "Valid" in this context means: either an address in the first MB ( conventional memory ) or the address of a - committed - memory block allocated with one of the DPMI memory functions. Address 300000h does not actually look like belonging to this set.

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MS-DOS forever!

> Sorry if this is an old age problem

it is

> I thought HDPMI32 would somehow intercept int 21h/AH=3F in protected mode

Every DPMI host does "intercept".

> and accept 32bit addressing unlike its 16bit counterpart ?

You can have ECX >= 64 KiB and EDX > 1 MiB but only with True DPMI (HDPMI: YES | WATCOM extenders: YES | CWSDPMI : NO), but the buffer must be valid ( see above and http://board.flatassembler.net/topic.php?t=6384 ).

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