Hello. I'm working on a own DOS-Like-Operating System, written with Flat Assembler (under Win3.11/DOS 6.22). Everything works fine - I'm using 80286-Instructions. I've tested the Bootloader and Kernel on 486SX, Pentium I, AMD Athlon and even on AMD Dual-Core CPUs. Its working fine. Today, I'm tested it on a real 80286 and it hangs - No CPU-Test (test Flags, if 80286 or higher is available), no INT $13 (Read Sectors). I'm absolutely sure, that all Commands are for 8086, 80186 and 80286. Is it possible, that FASM generates Codes for CPUs > 386 as default?

Have a look here for macros to ensure you only use 80286 codes. It has been extensively tested on real 80286's with no problem. You can't accidentally use eax or jmp dword xx etc.

I suspect the main problem is the jcc, this is a problem I also had with a genuine 80286 and I solved it with the macros in the link.

Thank you very much. I will try it I also think, that this is the problem, because even the first 5 lines doesnt work on the 286 (and there is ja JNZ xxxx).

Tell us if it works. Oh, and a screenshot or two wouldn't hurt.

(just glad to find another 16-bit person, heh)

P.S. Ever seen MikeOS? (NASM but still good, heh)

Maybe MiniDos may help, (a 2k Dos clone, coded in fasm).
http://board.flatassembler.net/topic.php?t=5275

It's true, FASM will generate 386+ jumps if it doesn't fit. Your best bet (besides above-mentioned macros or MCD's ONLY8086.INC) is to explicitly say "ja short Mylabel". At least then it will give you an error if it won't fit. (A simple regex search/replace via sed or your favorite editor should fix all such jump instructions in your sources for you.)

Sorry for the long break, I've took. But now, I'm back and the OS is still in Development Here is the homepage (german): www.geocities.com/timo_brueggmann and I attached a screenshot, running BonnyDOS on an IBM Thinkpad (the owner is a very good betatester )

At first, the Bootloader enables the A20-line, check the state and reads the kernel (at the moment 10,5K). Then the kernel is moved to the first 64K above the 1M. The Kernel is now active, checks the memory-config, and loads the command-line interpreter (about 5k) from disk. The SHELL executes a start-script, if available, and after that, SHELL is waiting for input At the moment, there are some internal commands (DIR, SORT, REN, DEL, EXECUTE, VERSION, ASK, PRINT, and some more) and a few commands on disk (INFO, DEVICE, PAR a resident Device, INSTALL). I hope, soon there are more commands and a complete HD-Support.

Looks nice. Good luck to you!