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Loading dos high on a XT

R

RuudB

Experienced Member
Joined
May 10, 2011
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158
Location
Heerlen - Netherlands
Hallo allemaal,


I expanded my XT with 128 KB of SRAM in the D- and E-area. For the schematics please see: http://www.baltissen.org/images/umb4xt.png
Using the right UMB driver I managed to LOADHIGH various drivers like ANSI.SYS and my mouse driver. But it didn't work out for DOS. It seems that HIMEM.SYS is reponsible and that program won't work on a XT.

My question: does anyone have an idea how I can persuade DOS to load itself high in my UMB memory?

One idea of myself: emulating INT 15h in one or another way but then: how to tell DOS to load itself into the UMB area instead of the not-existing HMA area?


Groetjes, Ruud Baltissen
www.Baltissen.org
 
Using PC-DOS 2000, USE!UMBS and DOSMAX I managed to load DOS in UMB memory with a self-made ISA ram card (similar to yours I think, but mine used two 64kb SRAM ICs and a 74LS138 )


20120117152513675.jpg
 
nestor said:
Using PC-DOS 2000, USE!UMBS and DOSMAX I managed to load DOS in UMB memory with a self-made ISA ram card (similar to yours I think, but mine used two 64kb SRAM ICs and a 74LS138 )
Click to expand...

nestor, can you please provide more details? :)

Here is my schematics for memory extension card. It allows mapping of up to 192 KiB memory (from 0C0000h to 0EFFFFh) to UMB, that can be enabled on 32 KiB block basis (depending on other devices that use high memory). It also adds memory in 80000h to 9FFFFh range (from 512KiB to 640 KiB), this could be disabled if needed.

Hopefully your method will make it work too. Also it is interesting if it is possible to have "holes" in UMB.
 
Also, look at the 1Meg mod for the 5160 using 4 banks of 256K DRAM and replacing the mapping ROM. It gives the same 128K between D0000 and EFFFF without adding any cards.
 
Chuck(G) said:
Also, look at the 1Meg mod for the 5160 using 4 banks of 256K DRAM and replacing the mapping ROM. It gives the same 128K between D0000 and EFFFF without adding any cards.
Click to expand...
I can testify for this! The 1MegXT mod works great. I get the same results as Nestor Using PC-DOS 2000, USE!UMBS and DOSMAX. The only drawback I can see is that we haven't figured out how to make it work on any of the XT clones.

Anyone with a True Blue IBM XT 5160 or 5155 interested in the 1megXT mod, let me know, either here or by PM. I can provide the GAL and Adapter for cost of shipping.
 
Chuck(G) said:
Also, look at the 1Meg mod for the 5160 using 4 banks of 256K DRAM and replacing the mapping ROM.
Click to expand...
I did the hack with an 8 MHz board. But my 10 MHz board has one big IC taking care of 90% of the functions of the board, including managing the DRAM. And that was the reason to build this card.
An advantage of this card: it doesn't needed to be initialised. If you don't do that with the DRAM, you surely get a parity error the first moment you access it. That's what happened I used USE!UMBS the first time with my 8 MHz board. I solved this problem by letting my BIOS taking care of this. How did you solve it?
 
RuudB said:
I did the hack with an 8 MHz board. But my 10 MHz board has one big IC taking care of 90% of the functions of the board, including managing the DRAM. And that was the reason to build this card.
An advantage of this card: it doesn't needed to be initialised. If you don't do that with the DRAM, you surely get a parity error the first moment you access it. That's what happened I used USE!UMBS the first time with my 8 MHz board. I solved this problem by letting my BIOS taking care of this. How did you solve it?
Click to expand...
Chuck wrote a little device driver View attachment CLEARMEM.ZIP
First line in config.sys(or one of the first before use!umbs.sys) would be "device=c:\clearmem.sys d000 2000" .
This will clear d000 thru efff (2000 paragraphs starting at d000), taking care of the parity error problem.

Here's the 1MegXT thread that Chuck reffed to. It's a little long but there's some good info in there.
 
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sergey said:
nestor, can you please provide more details? :)
Click to expand...

My memory extension card is very simple: a 74LS138 is used to chip-select a 64KB SRAM IC for D0000-DFFFF area and other 64 KB SRAM IC for the E0000-EFFFF area. That gives a 128 contiguous UMB memory, but the OS can't use them directly. Here enters USE!UMBS.SYS, a free driver that enables UMB using RAM in the D0000-EFFFF area. Once loaded, you can use loadhi and devicehigh to load drivers and trs in upper memory.

To load DOS itself in UMB, I use DOSMAX. It is a free driver to load DOS in UMB memory.
 
nestor said:
Here enters USE!UMBS.SYS
Click to expand...
IIRC I got the software from the developer himself in 1991. But just out of curiousity I searched the internet for it but couldn't find it. If there is interest, I'll put it on my site so others can download it. FYI, my version includes the source code.

To load DOS itself in UMB, I use DOSMAX.
Click to expand...
I found DOSMAX17.
One question: how does your CONFIG.SYS and AUTOEXEC.BAT look like?
 
RuudB said:
IIRC I got the software from the developer himself in 1991. But just out of curiousity I searched the internet for it but couldn't find it. If there is interest, I'll put it on my site so others can download it. FYI, my version includes the source code.


I found DOSMAX17.
One question: how does your CONFIG.SYS and AUTOEXEC.BAT look like?
Click to expand...

I found USE!UMBS here: http://cd.textfiles.com/cream/cream06/utility/ (look for use_umbs.zip file)
It comes with the source... the only thing that I will improve (if and when I have time) is command line options for specifying UMB memory ranges. Now it's just hard coded.
 
sergey said:
the only thing that I will improve (if and when I have time) is command line options for specifying UMB memory ranges.
Click to expand...
I already was working on a version that checks the memory itself. Not handy but I simply didn't think about the command line option. I only thought about when seeing the DOCs that goes with DOSMAX yesterday evening. From next week on I have time, so could you do me a favour and point me to an URL or give me instructions how I can check the command line using assembly?
Many thanks! Results will be freeware of course.
 
RuudB said:
I already was working on a version that checks the memory itself. Not handy but I simply didn't think about the command line option. I only thought about when seeing the DOCs that goes with DOSMAX yesterday evening. From next week on I have time, so could you do me a favour and point me to an URL or give me instructions how I can check the command line using assembly?
Many thanks! Results will be freeware of course.
Click to expand...

The command line (anything after DEVICE=...) is passed with the driver initialization call to the driver. The address to command line is stored in the request header starting from offset 12h (decimal 18 ), it is a 4-byte pointer with segment and offset. See this (look for "driver initialization call").

You'll need to implement parsing of the command line (validate its correctness, translate ASCII/hex to binary). Discussed in other thread 2M-ABIOS/2M-XBIOS floppy BIOS extension has a code for parsing device driver's command line. The source code can be found here (note: comments in the code are in Spanish). Perhaps this can be used as an example of command line parsing.

The USE!UMBS comes with memory auto-detection utility (TEST!UMB?!), but it looks not very reliable, e.g. it might report VGA memory or shared memory of an Ethernet card as UMBs, but I doubt anyone will want to use this memory for UMB purpose. So I don't think it is a great idea to implement auto memory detection in the driver itself.
 
I'm with sergey, auto-detection would be prone to misidentify unusable UMB RAM and honestly, the few people that are interested in using UMB in XT know exactly the amount and location of the UMB blocks.

Here are the contents of my actual AUTOEXEC.BAT / CONFIG.SYS files:

Code: 
@ECHO OFF
SET COMSPEC=C:\COMMAND.COM
SET PATH=C:\DOS
SET TEMP=C:\DOS
LH C:\DOS\MOUSE.COM
LH C:\DOS\DOSKEY.COM

Code: 
FILES=30
BUFFERS=20
COUNTRY=034,850,C:\DOS\COUNTRY.SYS
DOS=UMB,HIGH
DOSDATA=UMB
DEVICE=C:\USE!UMBS.SYS
DEVICE=C:\APPS\DOSMAX\DOSMAX.EXE /R+ /N+ /P-
DEVICEHIGH=C:\DOS\SETVER.EXE
DEVICEHIGH=C:\DOS\DISPLAY.SYS CON=(,,1)
DEVICEHIGH=C:\APPS\2M\2M-XBIOS.EXE A:4 B:0 /13
SHELL=C:\APPS\DOSMAX\SHELLMAX.COM C:\COMMAND.COM C:\ /E:256 /P
 
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Those of you who use USE!UMBS.SYS might be interested to know that I have added command line parameter support and also optimized it to reduce memory usage. My version (source+binary) is in the v2.1 folder in the attached zip-archive. The files in the archive root is the original version (v2.0).

View attachment USE!UMBS.ZIP

Example CONFIG.SYS command line for a single 128 KB UMB starting at segment D000h:
Code: 
DEVICE=USE!UMBS.SYS D000-EFFF

Try it and let me know what you think.
 
Just to be clear, loading DOS=HIGH means loading into the High Memory Area (the part right above 1Mb), which doesn't exist on an 8086.

DEVICEHIGH and LOADHIGH rather confusingly load into the Upper Memory Area, not the HMA.
 
Krille said:
Those of you who use USE!UMBS.SYS might be interested to know that I have added command line parameter support and also optimized it to reduce memory usage.
Try it and let me know what you think.
Click to expand...

I am now using your updated version with an IBM PC 5150 which has two original IBM 64/256KB Memory Expansion Option cards in it. These cards actually allow putting RAM into the A000-AFFF segment (typically used by EGA and VGA graphics cards). That configuration can be used if one has a CGA, Hercules or MDA display adapter.

Maybe you could implement the functionality of CLEARMEM.SYS into USE!UMBS.SYS with a parameter like /ZEROFILL which would write zeroes into the configured upper memory blocks.
 
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