Contents

• Tiny OS Kernel
• Page Translation tutorial
• V86 mode monitor tutorial
• Coff Utils and example programs
• Boot sector that loads and runs COM/EXE programs
• OS Development for Dummies - OS Loader
• Intel Manuals on x86 and x87
• http://welcome.to/pmode - a new PMode tutorial project I participate.
  My tutorials are made with use of free C and ASM compilers. ASM is used quite a little, so you may learn from the C code mostly which is much more easier.

I didn't have to do anything sometime ago and I started then programming an OS. It seems that I still don't quit starting serious, global and complex projects. ;))

I program the OS with my friend - Gennady Proschaev (we discuss details, find and fix bugs together). His coordinates go here:

- Those ones I've found myself are now fixed! ;)

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Two versions of the program (PAGING and NOPAGING) differ only in one  thing. The first one sets the PG bit of the CR0 register to "1", but the second  one doesn't do that. The result is also different. Programs draw colored bars on the screen in a different order.  That's because  Page Table  setup so that a linear address doesn't equal to a physical address everywhere. Detailed, order of pages that correspond to the VGA graphics buffer is opposite to the normal order.

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This program is intended to show how a V86 monitor should work. It sets up a V86 mode and launches a command interpreter (COMMAND.COM).

• Support for up to 8 nested IRQs in a V86 Mode
• Support for 87H function of a BIOS Int 15H
• An asterisk flashes at the top-right edge of the screen, mentioning that the V86 mode monitor works

Unfortunately, I discovered that this program sometimes doesn't work. There must be a bug which I'm not gonna fix because the source code is huge and old. Better visit the following site because v86 stuff presented there is much simpler and really works:

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Here goes a set of utils that allow you to make 32-bit programs for Protected Mode (not for DPMI!!!) very easily with DJGPP C compiler and/or NASM assembler. These utils simply make ready-relocated flat executable programs out of COFF ".o" object files. Such executable programs are really easy to load and run, since there is not needed relocation process any more. I've written all these utils because programming entire programs for PMode in pure x86 assembly language is too boring for me. I've been interested in how to use a C or Pascal compiler for that. So here they are...

• Standard file name extension for the flat executables is ".com" ;-). That's because these programs are ".com"-like. They contain a stub part that says something like a "Not a DOS or Windows program." and exits to the OS. The stub part also holds information needed for loading the pmode program (i.e. ID string, format and type of the file, file pointers to the .text and .data sections, sizes of the .text, .data and .bss sections plus actual size of the stack). The main util that converts COFFs to COMs is Coff2Com.exe.
• Since the flat executable pmode programs are not selfrun, there is also an util (OSLoader.exe) that loads such a pmode program, does all the needed setup (GDT, Interrupt Controller, Page Tables), switches to protected mode and runs loaded program.
• This package contains full well commented sources of the utils written for TASM3.2, DJGPP C 2.95.2 and NASM 0.98. Documentation is also included.
• Current versions are:

Coff2Com.exe - v1.4
OSLoader.exe - v2.2
I hope I've fixed all the bugs in these utils. New versions will out only with new features, I guess.
• Two example programs written in assembler and C shows how the package works.

C example program is more advanced:

• It handles exceptions (simply quits).
• It handles IRQs (0-timer, 1-keyboard, 3/4-standard serial mouse).

Note: None of IRQs is passed to Real Mode. There are only PMode handlers.
• It can read sectors of a HDD.
• It can perform software interrupts in V86 mode (it can set graphics mode using BIOS Int 10h service, for example).
• Simple memory manager has been implemented. It doesn't use all the advantages of page translation yet, but it will.
• The example program also have a few basic functions of a standard C run-time library.
• Current version of the exapmle program is 1.0 (23th of January, 2000).

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Why not to make a boot sector capable to load and run standard COM and EXE programs? You would have the only bootsector and it woudn't be changed each time when you changed something in the project. Why not to add there support for FAT and load a program regardless of place where it starts on the disk?

Do you like this idea? If so, check out my BootProg boot sector that does the job very well.

Current version (v1.2) of the boot sector is intended for use on standard diskettes that have FAT12 and primary DOS HDD partitions both FAT12 and FAT16. I tested it on the both FDD and HDD.

I hope you understand that programs loaded by the boot sector must not call MSDOS service functions. You may use BIOS services instead.

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