自己动手写造作系统(源代码)随书光盘

WHAT IS THIS? ============= Sample protected-mode code, in increasing order of complexity: * Basic 32-bit protected mode. * Access to text-mode video memory. * Linear (flat) memory. * Return to real mode. * PM interrupts/exceptions. * Test for Virtual 8086 mode. * PM text-output subroutine. * CPU detection (386 or better). * Software interrupt validation. * "Unreal" mode (flat real, big real). * Copying code to alternate memory location and running it there. * Enabling A20 gate. * Running code in extended memory. * Simple task state segment (TSS) use. * Preemptive multitasking via timer interrupt. * Ring 0 (kernel/system mode) code to/from Ring 3 (user mode) code. * Syscalls. * Reprogramming 8259 interrupt chip. * Interface/linking to C-language code. * Beginnings of a libc. * More elaborate syscalls/exception handler. * Scrolling video and cursor movement. PM1.ASM is heavily commented, and tries to serve as a tutorial. The .ASM files are written in x86 assembly language and should be assembled with NASM (the free x86 assembler) like this: nasm -o pmXXX.com pmXXX.asm I am also including the PM12C.C file, which needs DJGPP, the free 32-bit C compiler for MS-DOS. A pre-compiled version of NASM 0.97 that I downloaded from the Internet gave me a lot of grief. The problems went away after I downloaded the NASM sources and compiled them myself under DJGPP. Be warned. These programs assume a 386 or better CPU (386 SX/DX, 486 SX/DX, Pentium, Pentium II, non-Intel clone processors, etc.). WHERE IS THIS? ============== http://www.execpc.com/~geezer/os/pm.zip WHAT CAN I DO WITH THIS? ======================== Anything you want, so long as you don't - take credit for something you didn't do, or - blame me for the results. WHY DOESN'T IT WORK? ==================== See KNOWN BUGS, below. "My computer freezes up!" pm10 and later programs do not include code to return to real mode: after doing their thing, they freeze. Press the reset button or cycle power to reboot. "It doesn't freeze up but nothing gets printed." These apps put text on the top line of the screen by writing directly to video memory. If the cursor is at the bottom of the screen when you type pm1 (or whatever), the output of the program will get scrolled off the top of the screen after it returns to DOS. Try cls pm1 (or whatever) (thanks to Mark for the heads-up on this). "These programs freeze up my computer without printing anything." pm6 will crash if extended memory is in use (e.g. by SMARTDRV). If the crash is happening in other situations, please let me know about it. "The computer just reboots." Again, this shouldn't happen (and again, let me know if it does). Bad protected-mode code often makes the CPU triple-fault, which causes the computer to reset itself. Hopefully, this code is simple enough that it shouldn't have any bugs. "Windows 95 says 'MS-DOS mode' and terminates the program." These programs won't run under Windows. MS-DOS mode might work, but it's better to reboot the computer, wait for 'Starting Windows 95...' and quickly press F8. Then chose 'Safe mode command prompt only' and run these files. "EMM386 privileged operation error..." Same problem as Windows (CPU is in Virtual 8086 mode). If you are loading EMM386.EXE in CONFIG.SYS, comment it out. Or use the F8 boot option described above. The EMM386 that comes with Win95 lets you press 'C' to disable EMM386 and continue, which may or may not work. "Nothing happens, no 'Hello' or reboot -- it just returns to DOS." pm3.asm through pm6.asm return to DOS if Virtual 8086 mode is detected (Windows DOS box or EMM386). pm4.asm through pm6.asm return to DOS if an 8088 or 80286 CPU is detected (though this hasn't been tested). Type test pm3 and look at the output. If it says Program 'pm3' returned errorlevel 1. then the CPU is in Virtual 8086 mode (Windows DOS box or EMM386 in use). If you type 'test pm4' and get Program 'pm4' returned errorlevel 2. this means the CPU is not a 386 or better. WHERE'D YOU LEARN TO DO THIS? ============================= Freedows '98 -- Copyright (C) 1997 Joachim Breitsprecher <j.breitsprecher@schwaben.de> Benn Vosseteig posted some spiffy Ring 0-to-Ring 3 code on the OS development board at http://milkyway.isa.net.au/os-dev/cgi-bin/blueboard.exe Linux -- Copyright (C) 1991, 1992 Linus Torvalds I recommend the 'Historic' kernel (version 0.01), available from http://www.kernel.org/pub/linux/kernel/Historic/linux-0.01.tar.gz INTEL 80386 PROGRAMMER'S REFERENCE MANUAL 1986, available from http://www.execpc.com/~geezer/os/386intel.zip and many other sites. Robert Collins' "Intel Secrets" web site: http://www.x86.org Josh McDonald's OS/2000 http://www.effect.net.au/os-dev/ KNOWN BUGS ========== One task of pm8 seems to die if run indefinitely instead of only 18 times (maybe this is some kind of weird resonance). FEEDBACK ======== ...is welcome. Christopher Giese <geezer[AT]execpc.com>