CSE140 Project 1 solved


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In this project, you will create an instruction interpreter for a subset of MIPS code. Starting
with the assembled instructions in memory, you will fetch, disassemble, decode, and
execute MIPS machine instructions, simulating each stage in the computation. You’re
creating what is effectively a miniature version of MARS! There is one important difference,
though—MARS takes in assembly language source Hiles, not .dump Hiles, so it contains an
assembler, too.
You may work with a partner for this project. Each person will turn in the following for the
project on CatCourses:
• Completed computer.c
• Testing.txt/doc which outlines your testing strategy
• All the *.s and *.dump Hiles you used to test your project in test.tgz
• Name of your partner in the submission box.
Project Speci,ication
The Hiles sim.c, computer.h, and computer.c comprise a framework for a MIPS
simulator. Complete the program by adding code to computer.c. Your simulator must be
able to simulate the machine code versions of the following MIPS machine instructions:
addu Rdest, Rsrc1, Rsrc2
addiu Rdest, Rsrc1, imm
subu Rdest, Rsrc1, Rsrc2
sll Rdest, Rsrc, shamt
srl Rdest, Rsrc, shamt
and Rdest, Rsrc1, Rsrc2
andi Rdest, Rsrc, imm
or Rdest, Rsrc1, Rsrc2
ori Rdest, Rsrc, imm
lui Rdest, imm
slt Rdest, Rsrc1, Rsrc2
beq Rsrc1, Rsrc2, raddr
bne Rsrc1, Rsrc2, raddr
j address
jal address
jr Rsrc
lw Rdest, offset (Radd)
sw Rsrc, offset (Radd)
Refer to the handout attached in the assignment page which contains the binary code of the
MIPS instructions. Once complete, your solution program will be able to simulate real
programs that do just about anything that can be done on a real MIPS, with the notable
exceptions of Hloating-point math and interrupts.
The framework code
1. It reads the machine code into “memory”, starting at “address” 0x00400000. (In
keeping with the MARS convention, addresses from 0x0000000 to 0x00400000
are unused.) We assume that the program will be no more than 1024 words long.
The name of the Hile that contains the code is given as a command-line argument.
2. It initializes the stack pointer to 0x00404000, it initializes all other registers to
0x00000000, and it initializes the program counter to 0x00400000.
3. It provides simulated data memory starting at address 0x00401000 and ending at
address 0x00404000. Internally, it stores instructions together with data in the
same memory array.
4. It sets Hlags that govern how the program interacts with the user.
It then enters a loop that repeatedly fetches and executes instructions, printing information
as it goes:
• the machine instruction being executed, along with its address and disassembled
form (to be supplied by your PrintInstruction function);
• the new value of the program counter;
• information about the current state of the registers;
• information about the contents of memory.
The framework code supports several command line options:
As discussed in lecture, Fetch, Decode, Execute, Mem, and RegWrite are the Hive
processing stages of the MIPS archetecture. In our simulator, these steps involve completing
the following tasks. The Fetch step has been implemented for you so you job is to Hill in the
remaining functions:
• Decode – Given an instruction, Hill out the corresponding information in a
DecodedInstr struct. Perform register reads and Hill the RegVals struct. The
addr_or_immed Hield of the IRegs struct should contain the properly extended version
of the 16 bits of the immediate Hield.
• Execute – Perform any ALU computation associated with the instruction, and return
the value. For a lw instruction, for example, this would involve computing the base +
the offset address. For this project, branch comparisons also occur in this stage.
• Mem – Perform any memory reads or writes associated with the instruction. Note
that as in the Fetch function, we map the MIPS address 0x00400000 to index 0 in
our internal memory array, MIPS address 0x00400004 to index 1, and so forth. If
an instruction accesses an invalid memory address (outside of our data memory
range, 0x00401000 – 0x00403fff, or not word aligned for lw or sw), your code
must print the message, “Memory Access Exception at [PC val]: address [address]”,
where [PC val] is the current PC, and [address] is the offending address, both printed
in hex (with leading 0x). Then you must call exit(0).
• RegWrite – Perform any register writes needed.
runs the program in “interactive mode”. In this mode, the program prints a “>”
prompt and waits for you to type a return before simulating each instruction. If
you type a “q” (for “quit”) followed by a return, the program exits. If this option
isn’t specified, the only way to terminate the program is to have it simulate an
instruction that’s not one of those listed on the previous page.
prints all registers after the execution of an instruction. If this option isn’t
specified, only the register that was affected by the instruction should be printed;
for instructions which don’t write to any registers, the framework code prints a
message saying that no registers were affected. (Your code needs to signal when
a simulated instruction doesn’t affect any registers by returning an appropriate
value in the changedReg argument to RegWrite.)
prints all data memory locations that contain nonzero values after the execution
of an instruction. If this option isn’t specified, only the memory location that was
affected by the instruction should be printed; for any instruction that doesn’t
write to memory, the framework code prints a message saying that no memory
locations were affected. (Your code needs to signal when a simulated instruction
doesn’t affect memory by returning an appropriate value in the changedMem
argument to Mem.)
-d is a debugging flag that you might find useful.
In the case of an unsupported instruction, make sure that you call exit(0) somewhere
in your code, before PrintInfo and fetching the next instruction. Do not print any
special error message in this case..
In the UpdatePC function, you should perform the PC update associated with the current
instruction. For most instructions, this corresponds with an increment of 4 (which we have
already added).
The PrintInstruction function prints the current instruction and its operands in text.
Here are the details on the output format and sample.output Hile contains the expected
output for sample.dump:
• The disassembled instruction must have the instruction name followed by a “tab”
character (In C, this character is ‘\t’), followed by a comma-and-space separated list
of the operations.
• For addiu, srl, sll, lw and sw, the immediate value must be printed as a decimal number
(with the negative sign, if required) with no leading zeroes unless the value is
exactly zero (printed as 0).
• For andi, ori, and lui, the immediate must be printed in hex, with a leading 0x and no
leading zeroes unless the value is exactly zero (which is printed as 0x0).
• For the branch and jump instructions (except for jr), the target must be printed as a
full 8-digit hex number, even if it has leading zeroes. (Note the difference between
this format and the branch and jump assembly language instructions that you
write.) Finally, the target of the branch or jump should be printed as an absolute
address, rather than being PC relative.
• All hex values must use lower-case letters and have the leading 0x.
• Instruction arguments must be separated by a comma followed by a single space.
• Registers must be identiHied by number, with no leading zeroes (e.g. $10 and $3) and
not by name (e.g. $t2).
• Terminate your output from the PrintInstruction function with a newline.
• As an example, for a store-byte instruction you might return “sb\t$10, -4($21)\n”.

Here are examples of good instructions printed by PrintInstruction:
addiu $1, $0, -2
lw $1, 8($3)
srl $6, $7, 3
ori $1, $1, 0x1234
lui $10, 0x5678
j 0x0040002c
bne $3, $4, 0x00400044
jr $31
Here are examples of bad instructions:
# shouldn’t print hex for addiu
addiu $1, $0, 0xffffffff
# shouldn’t print hex for sw
sw $1, 0x8($3)
# should use reg numbers instead of names
sll $a1, $a0, 3
# no spaces between arguments
srl $6,$7,3
# forgot commas
ori $1 $1 0x1234
# hex should be lowercase and not zero extended
lui $t0, 0x0000ABCD
# address should be in hex
j 54345
# forgot the leading 0x
jal 00400548
# needs full target address in hex
bne $3, $4, 4
The Hiles sample.s and sample.output provide an example output that you may use
for a sanity check. We do not include any other test input Hiles for this project. You must
write the test cases in MIPS, use MARS to assemble them, and then dump the binary code.
You will need to submit everything you used to test your project.
MARS places anything that follows the .data assembler directive sequentially in memory.
However, this will not be reHlected in the binary Hile that MARS dumps. That dump Hile only
contains instructions. Therefore, instead of depending on MARS to load data memory for
you, you should use instructions. For example, suppose you want to write a MIPS program
that uses an array of 5 words called foo which is initialized with the integers 1, …, 5.
Normally, you would write something like:
foo: .word 1,2,3,4,5
For this project, you would not use the .data section. Instead you would have your program
initialize the array:
lui $t0, 0x1001
ori $t0, 0x0000
addiu $t1, 1
sw $t1, 0($t0)
addiu $t1, 2
sw $t1, 4($t0)
addiu $t1, 3
sw $t1, 8($t0)
addiu $t1, 4
sw $t1, 12($t0)
addiu $t1, 5
sw $t1, 16($t0)
You could also do this in a loop. This may seem a bit tedious and time consuming but it
greatly simpliHies the simulator.