CS 630

PROJECT #1                             Due Date: Noon Tuesday 02/17/2004


     This project acquaints students with programming issues which arise
in the use of 'as86' assembly language to create a 'boot-sector' program
that will be executed by the Pentium processor in Real-Mode.   


                          PROBLEM DESCRIPTION

     Design an enhanced version of the 'regdump.s' bootsector program so 
that it will display the initial values in all of the Pentium's (32-bit) 
general registers and control registers, plus the six segment-registers. 
(The program code you write for this project will serve as the basis for 
a useful diagnostic debugging tool in some later programming exercises.)
One suggested format for your screen-display is depicted below:



	00000000=EAX  00000000=EBX  00000000=ECX  00000000=EDX
	00000000=ESP  00000000=EBP  00000000=ESI  00000000=EDI
	00000000=CS   00000000=DS   00000000=ES   00000000=FS 
	00000000=GS   00000000=SS   00000000=EIP  00000000=EFL
	00000000=CR0  00000000=CR2  00000000=CR3  00000000=CR4



You will need to consider carefully the sequence in which you access the
various registers, to be sure you are not introducing any alterations to
their original contents prior to saving them.  (Remember that any use of
arithmetical or logical instructions will alter the value of status bits
in the EFLAGS register, whereas the use of data-transfer instructions is
generally "safe" insofar as affecting the EFLAGS register is concerned.)   
You will also need to keep in mind that your 'bootsector' is constrained 
to occupy exactly 512-bytes (including the 2-byte boot-signature).  This
means you must write assembler code that is space-efficient.  Upon entry
to your program, the CS:EIP registers will have known values (CS=0x0000,
EIP=0x00007C00) as a consequence of standardized ROM-BIOS conventions in
the Power-On Self-Test bootstrap loader, but the initial values in other
processor registers are not subject to such a standard (and tend to vary
widely among PC platforms).  In particular, special caution is needed in
using the initial stack space, whose size will be unknown to you, as the
stack-size may be very limited, and may be located in a region of memory 
that is adjacent to some vital system data-structures (such as the table
of interrupt vectors, or the ROM-BIOS DATA-AREA).  You could switch to a
larger-size stack, located in a "safe" area of physical memory; however,
you'd need to be sure you've saved the original SS:ESP before doing so.


                             WHAT TO SUBMIT

     Place the assembly language source-text into your '/submit' folder,
along with your binary output-file produced by the 'as86' assembler, and
turn in a printed copy of your source-text to the Instructor's mailbox.

________________________________________________________________________
Allan B. Cruse        University of San Francisco            Spring 2004