CS 630

PROJECT #2                             Due Date: Noon Tuesday 04/06/2004

     This project explores essential steps in crafting minimal operating 
system code that can load and execute the object-code within an ELF file 
that was compiled for Linux, running in protected-mode on a Pentium CPU.

                          PROBLEM DESCRIPTION

     Design a miniature operating system (named 'os630.s') which can run
the 'manydots.s' demo-program (found on our course website) at privilege
level 3 in protected mode.  You will need to implement your own handlers 
for the timer-tick and keyboard interrupts, and for Linux's system-calls
(invoked via the 'int 0x80' software interrupt instruction).  You should
reprogram the 8259A Interrupt Controllers to issue the device-interrupts
in a manner that avoids conflicts with Intel reserved interrupt-numbers.     
Your operating system should continuously show the time-of-day onscreen,
using a status-line separate from the normal console-output screen area.

     Download the demo-program named 'manydots.s' from our class website
and assemble it using the GNU/Linux assembler 'as' to produce a linkable 
ELF-file (named 'manydots.o'), like this:

		     $ as manydots.s -o manydots.o

Then use the 'dd' utility to install the 'manydots.o' ELF-file onto your
floppy diskette, starting from sector #14 of track 0, like this:  

		$ dd if=manydots.o of=/dev/fd0 seek=13

This insures that the ELF-file's contents will get loaded into memory as
you 'boot' from this diskette, assuming our 'trackldr.b' boot-loader was
installed in the 'boot-sector' as usual, like this:

	            $ dd if=trackldr.b of=/dev/fd0 

The final step, in preparing your diskette for submission, is to install 
your operating system binary (i.e., 'os630.b') on the diskette following
the boot-sector, like this:

	          $ dd if=os630.b of=/dev/fd0 seek=1

It is vital that the filesize of your 'os630.b' binary should not exceed
six kilobytes (i.e., twelve diskette sectors), to avoid overwriting your
ELF-file's image which begins in sector #14, as shown below:

                    SECTOR-MAP FOR DISKETTE TRACK 0  

          sector #1      sectors #2-#13       sectors #14-#18
       +-------------+-------------------+----------------------+
       | boot-loader | <--- os630.b ---> | <--- manydots.o ---> |
       +-------------+-------------------+----------------------+
      
     Place the assembly language source-text into your '/submit' folder,
along with your binary output-file produced by the 'as86' assembler, and
put your diskette and source-text printout in the Instructor's mailbox.
________________________________________________________________________
Allan B. Cruse        University of San Francisco            Spring 2004