LOADALL for 286 #1562
Replies: 9 comments 3 replies
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https://www.pcjs.org/documents/manuals/intel/80286/loadall/ wikipedia a bit short on details, this linkk from 0os2 museum comments goes into details |
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Hello @Randrianasulu, I'm familiar with the undocumented 286 LOADALL instruction, it essentially performs the same thing as the 386+ does with "unreal mode" by caching a base address greater than 1M for support of more than 20 address lines without having to switch into protected mode. The question is, what exactly are you looking for? ELKS can't use any DOS or Microsoft XMS programs, as ELKS doesn't support DOS in any way. That is, we can't load or use HIMEM.SYS or any of its derivatives within ELKS. ELKS does support using XMS memory though, and uses 386+ unreal mode to directly access XMS memory, which is used to greatly increase the number of system buffers by moving them out of main (address 640kb or less) memory. However, in general, many BIOS's won't support ELKS reloading the segment cache registers, or they reset them themselves. This means we have to use BIOS INT 15h for block copy, which is likely not present in 286 BIOSes (we would need to check). The other bigger issue will be testing LOADALL on 286 - I don't have a 286 development system. Thank you! |
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@ghaerr I think this article from os2 museum (linked from wikipedia) says 286 will be seriously incompatible if it omits this instruction http://www.os2museum.com/wp/more-on-loadall-and-os2/ see also errata page in pdf document on pcjs link... For testing - I guess if 86Box in 286 mode can handle OS/2 1.X and/or ms dos's himem.sys you can try this for prototyping. Also, i386/XMS ELKS kernel must be compiled by user right now? |
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What feature are you looking for on 286? Just the use of extended buffers, or something else?
Yes. For the v0.6.0 (or was it 0.5.0?) release, an image was produced with XMS turned on, but it wouldn't boot on some systems, due to some incompatibility in A20 line handling, unreal mode used within BIOS vs INT 15, and 386 chip identification working properly, so we took it out. |
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As usual - big ramdisk, may be swap (I tried Minix 2.x on 86Box git, it boots correctly on 1 mb 286 machine and says it runs in protected mode). https://github.com/davidgiven/minix2 Only after reading again on 64+64 kb I/d split I realized WHY minix (and QNX ) were so proud about their microkernel design. Well, they ranon earlier x86 processors, before i386 become mainstream and cheap! Also UNIX philosophy at least partially may come from same - earliest unix was running on less than 32bit cpu :) as aside, 86box git apparently can serial passthru now (not tested, just saw commit messages some time ago, and now qt5 gui alliw you to set it up ...) |
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ELKS doesn't currently support any swap device nor ram disks that aren't in main memory. Extending the ramdisk to use unreal mode/INT 15h or possibly LOADALL may not be too much work. I've added that to my (large) list. Yes, ELKS is also limited to 64k+64k split I/D, and doesn't use any instructions other than 8086 (no 80186 or 286), except in the case of XMS initialization using unreal mode for buffer copying. If INT 15h XMS copy is compiled in, no 386 instructions are used, as the BIOS handles XMS copies. What do you mean serial passthru for 86box? Have you tried QEMU, it works well for ELKS and supports serial input/output/console. |
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well, I come from.qemu to pcem/86box others after realizing high-end dx4/100 qemu emulates as minimum still different even from earlier 486! I mean in theory you can connect virtual serial port from 86box to some ... pipe or pseudoterminal, I saw people here complained 86box can't do this. Now it hopefully can :) |
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I noticed link to this project on VOGONS forum, not quite ibm machine, but author hopes to get dos running there |
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https://archive.org/download/DesignOfOS2/Design%20of%20OS2.pdf this was recommended on reddit thread about 286 protected mode programming. |
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oh, 500+ pages! |
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thread on microcode from 80186 https://forum.vcfed.org/index.php?threads/8088-8086-microcode-disassembly.77933/page-2#post-951895 also, s100 boards site has some info http://www.s100computers.com/My%20System%20Pages/FPGA%2080286%20SBC/80286%20SBC.htm somewhat random link tells us 286 part is obsolete for 6 years already (in 2017). But may be someone will finally implement it in fpga. https://electronics-sourcing.com/2013/05/30/intel-amd-and-nec-x86-processors-re-created/ |
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https://rep-lodsb.mataroa.blog/blog/intel-286-secrets-ice-mode-and-f1-0f-04/ |
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I recognize it was considered out-of-scope for this project to support 286 specific features, but anyway because wikipedia link to himem 2.06 sources currently not answering and not archived I think I post this link here
https://archives.scovetta.com/pub/power_programming/MICROSFT/
https://archives.scovetta.com/pub/power_programming/MICROSFT/XMS20.ARC
for unpacking I installed unar utility (uses gnustep libs!) in termux, and now after unpacking SECOND arc archive inside I can read said function, even if I do not understand it :) apart from english comments. :)
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