Real Mode Programming

[n00b13]

Hi everyone,

I am trying to learn OS fundamental from a programmers perspective and currently studying on real mode programming.I have experience with protected mode but never actually did something in real mode.

I searched around to see if I can grab some tutorials or etc but nothing significant especially for C (most of them are for assembly)

My question is;

I wrote a program in C for protected mode and it works as expected.It does basic disk I/O read() and write(), in real mode I know these functions are available through "int 13" but I have no clue where to start in C.

Can I switch to or simulate real mode while linux is running ? Is there such a feature?

Also I would like to know how to port protected mode code to real mode so that ported code will only use bios interrupts.

Any ideas and help are welcomed!

Thank you

[gerard4143]

This may interest you...Then again it my not

bcc(1): Bruce's C compiler - Linux man page

Check the 'see also' at the bottom of the man page

Plus this one

SourceForge.net: Linux Real Mode Interface - Project Web Hosting - Open Source Software

[n00b13]

I know that I need to swtich to vm to call real mode interrupts from protected, but coudln't find a resource that explains the process of this.

I mean I can only do bios interrupts from real mode but how about porting a protected mode code to real thats where I am stuck.

Seabios seems really interesting though, I will check it out.

[gerard4143]

I know that I need to swtich to vm to call real mode interrupts from protected, but coudln't find a resource that explains the process of this.

I mean I can only do bios interrupts from real mode but how about porting a protected mode code to real thats where I am stuck.

Seabios seems really interesting though, I will check it out.

The only time I used real mode was with a boot disk...As for porting a protected mode code to real mode code - is that even practical.

Your first question can be answered by reading the CPU docs - Intel or AMD provide full documentation.

[rcgreen]

You're probably better off working in DOS.
Install dosemu. It is a way to run a DOS session under
Linux. You can then run a real mode C compiler like PCC
as well as any assembler you choose to write assembly code.

With dosemu, you can run your own copy of DOS, or the default
install of freedos

[Rubberman]

The dosemu package might work for you, or you can run DOS in a virtual machine and learn all about real-mode programming and bios interrupt handling all you want without jeapordizing your system. Do run it on hardware that support hardware virtualization however, to better protect your host OS.