majid@citycs.UUCP (M Mirmehdi) (09/15/89)
Hi,
Can anyone help with the following please:
I am writing an application on my 1MB PC-AT, using Microsoft C 5.1,
which requires a number of large two-dimensional arrays. Naturally,
having soon ran out of space in my conventional memory, I realised
that I had to explore the HMA or the EMB, where:
----------------------------------- Top of Memory
| |
| |
Please Note: -----------------------------------
This is a | Possible Extended Memory |
very basic | Block (EMB) |
representation. -----------------------------------
| |
----------------------------------- 1088K
| High Memory Area (HMA) |
___________________________________ 1024K or 1MB
-----------------------------------
| |
| Upper Memory Block |
----------------------------------- 640K
| Conventional Memory |
----------------------------------- 0K
I then requested LIMXMS (eXtended Memory Specification, ver 2.0)
from Microsoft, who promptly supplied me with a copy. I dismissed
the HMA immediately as I realised an extra 64K was not enough,
and tried to use the EMBs with the extra 384K available.
Using the test programs provided with LIMXMS, I managed to
confirm that I had 384K available, but the rest has been an uphill
struggle. I have tried to allocate (which seems to work fine)
and lock an area of memory (also works fine), and then assign it
to an array (code below) . It all works ok, but when I try to
initialise the array the whole system locks up.
/* Code to assisgn EMB to a 2D array of 100x100 size */
/* This is essentially like mallocing in conventional memory */
long far *start, *base;
long far **array;
long XMM_memory_start; /* eXtended Memory Manager start of memory */
/* This XMM_memery_start address is available after a LIMXMS procedure call */
start = (long far *)XMM_memory_start;
array = (long far **)XMM_memory_start;
base = start + 100;
for (i=0;i<100;i++) {
*start = (long far)&base;
start++;
base += 100;
}
/* now use array, but it hangs the system. */
Reading the LIMXMS documentation further, it seems that I have
two ways out, but these two methods are far two cumbersome and
tedious:
1 - Use the Move Block (function 0Bh) to move blocks of memory
around from conventional to extended memory. This would slow
down everything so much.
2 - Write driver routines which will exist in HMA which then access
the extended memory. No thanks!
I am probably wrong about (1) and completely misguided about (2),
but if anyone has any suggestions, however remote, please
mail me personally if possible. I will try and let the net know
how things get on. Has anyone done (1) or (2)?
I believe there are some articles in the Microsoft Journal which
help you out with this, (any old examples would do), but I
haven't managed to get hold of the relevant issues. I believe
there are helpful articles in:
"Microsoft Systems Journal", volume 10, number 6, November, 1988,
article entitled "The High Memory Area: 64KB More Memory in
Real Mode", by Chip Anderson, pages 53-57.
"Microsoft Systems Journal", volume 4, number 4, July 1989,
article entitled "Extended Memory Specification 2.x: Taking
Advantage of the 80286 Protected Mode", by Chip Anderson,
pages 17-26. (Thanks to Lee Fisher for references.)
Photocopies of these articles will be priceless!
I have just begun investigating the protected mode documentation
that I have so may be that will bring some joy.
Anyway, any help would be greatly appreciated.
Thanks in advance...
Majid.
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Majid Mirmehdi
Dept. of Computer Science
The City University
Northampton Square Tel : +44 1 253 4399 x3718
London Internet: majid%uk.ac.city.cs@nss.cs.ucl.ac.uk
EC1V 0HB JANET : majid@uk.ac.city.cs
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