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COMPSCI 210 Assignment
This assignment aims to give you some experience with C programming and to help you gain better understanding of the ISA of LC‐3.
Important Notes
There are subtle differences between various C compilers. We will use the GNU compiler gcc on login.cs.auckland.ac.nz for marking. Therefore, you MUST ensure that your submissions compile and run on login.cs.auckland.ac.nz. Submissions that fail to compile or run on login.cs.auckland.ac.nz will attract NO marks.
Markers will compile your program using command “gcc –o name name.c” where name.c is the name of the source code of your program, e.g. part1.c. That is, the markers will NOT use any compiler switches to supress the warning messages.
Markers will use machine code that is different from the examples given in the specifications when testing your programs.
The outputs of your programs will be checked by a program. Thus, your program’s outputs MUST be in the EXACTLY SAME FORMAT as shown in the example given in each part. You must make sure that the registers appear in the same order as shown in the example and there are no extra lines.
The files containing the examples can be downloaded from Canvas and unpacked on server with the command below:
o tar xvf A2Examples.tar.gz
As we need to return the assignment marks before the exam of this course, there is NO possibility to extend the deadline for this assignment.
Academic Honesty
Do NOT copy other people’s code (this includes the code that you find on the Internet).
In this assignment, you are required to write C programs to implement a LC‐3 emulator. That is, the programs will execute the binary code generated by LC‐3 assembler.
1
Part 1 (40 marks)
LC3Edit is used to write LC‐3 assembly programs. After a program is written, we use the LC‐3 assembler (i.e. the “TranslateAssemble” function in LC3Edit) to convert the assembly program into binary executable. The binary executable being generated by LC3Edit is named “file.obj” where “file” is the name of the assembly program (excluding the “.asm” suffix). In this specification, a “word” refers to a word in LC‐3. That is, a word consists of two bytes. The structure of the “file.obj” is as below:
The first word (i.e. the first two bytes) is the starting address of the program.
The subsequent words correspond to the instructions in the assembly program and the
contents of the memory locations reserved for the program using various LC‐3 directives.
In LC‐3, data are stored in Big‐endian format . For example, if byte 0x12 in word 0x1234 is stored at address 0x3000, byte 0x34 is stored at address 0x3001. This means, when you read a sequence of bytes from the executable of
an LC‐3 assembly program from a file, the most significant bit of each word is read first. In this part of the assignment, you are required to write a C program to display each word in the “.obj” file of a program in hexadecimal form. That is, the C program should display each binary number stored in the “.obj” file in it 汇编代写 corresponding hexadecimal form.
Name the C program as “part1.c”.
The name of the “.obj” file (the name of the file INCLUDES the “.obj” suffix) must be
given as a command line argument. The number of instructions in the file is NOT
limited.
In the output, each line shows the contents of one word.
The value of each word must have a “0x” prefix.
The letter digits “a” to “f” must be shown as lowercase letters.
Here is an example of the execution of the program. In this example, the LC‐3 assembly program is as below. The name of the executable of the assembly program is “p1.obj” (markers will probably use a file with a different name and different contents).
.ORIG X4500
LD R0, A
LEA R1, B
LDI R2, C
AND R3, R0, R1 AND R3, R1, #0 NOT R4, R3
ADD R4, R4, #1 BRp F
ADD R3, R3, #1
2
F HALT
A .FILL X560A
B .FILL X4507
C .FILL X4501
.END
The execution of the program is shown below. In this example, the name of the file containing the machine instructions is p1.obj (NOTE: “p1.obj” is the exact name of the file. That is, the file name does NOT have a ‘.txt’ suffix.). The command line argument is marked in red.
$ ./part1 p1.obj
0x4500
0x2009
0xe209
0xa409
0x5601
0x5660
0x98ff
0x1921
0x0201
0x16e1
0xf025
0x560a
0x4507
0x4501
Part 2 (26 marks)
In this part, you are required to write a C program to implement a LC‐3 emulator that is capable of executing instruction “LD”.
Name the C program as “part2.c”.
The name of the “.obj” file (the name of the file INCLUDES the “.obj” suffix) must be
given as a command line argument. The number of instructions in the file is NOT
limited.
It should be assumed that the “.obj” file contains at most 100 LC‐3 machine instructions.
The state of the emulator consists of the contents of the 8 general purpose registers (i.e.
R0 to R7), the value of the program counter (i.e. PC), the contents of the instruction
register (i.e. IR), and the value of the condition code (i.e. CC).
The values in R0 to R7, PC and IR should be shown as hexadecimal value. The value of CC
is either N, Z or P.
Before the emulator starts executing a program, it should first display the initial state of
the LC‐3 machine. In the initial state, R0 to R7 and IR should all be 0; PC should be the
starting address of the program to be executed; and CC should be set to Z.
When displaying the value of R0 to R7, PC, IR and CC, a tab character (denoted as “\t” in
C) is used to separate the name of the register and the value of the register. 3
Each hexadecimal value must have a “0x” prefix. The letter digits “a” to “f” must be shown as lowercase letters.
After showing the initial state, the emulator should execute each instruction except the “HALT” pseudo instruction in the “.obj” file. For this part, the emulator should display the hexadecimal code of each LD instruction that has been executed and the state of the LC‐3 machine after each LD instruction is executed. The hexadecimal code of an instruction is the hexadecimal form of the 16 bits used to represent the instruction. The hexadecimal code of each LD instruction should be preceded with “after executing instruction\t” (where \t denotes a tab character) and “0x”.
The emulator should output a line consisting of 18 “=” after displaying the state of the LC‐3 machine.
When the execution reaches the “HALT” instruction, the emulator terminates.
Here is an example of the execution of the program. In this example, the LC‐3 assembly program is as below. The name of the executable of the assembly program is “p2.obj” (NOTE: “p2.obj” is the exact name of the file. That is, the file name does NOT have a ‘.txt’ suffix). Markers will probably use a file with a different name and different contents.