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MARS - Mips Assembly and Runtime Simulator

Release 4.5

August 2014

Using MARS from a command line.

MARS can be run from a command interpreter to assemble and execute a MIPS program in a batch fashion. The format for running MARS from a command line is:

java -jar mars.jar [options] program.asm [more files...] [ pa arg1 [more args...]]

Items in [ ] are optional. Valid options (not case sensitive, separated by spaces) are:

aassemble only, do not simulate1.0
aenterminate MARS with integer exit code n if assembly error occurs4.1
asciidisplay memory or register contents interpreted as ASCII codes. (alternatives are dec and hex)4.1
bbrief - do not display register/memory address along with contents2.2
ddisplay MARS debugging statements (of interest mainly to MARS developer)1.0
dbMIPS delayed branching is enabled.3.3
decdisplay memory or register contents in decimal. (alternatives are ascii and hex)2.2
dumpdump memory contents to file. Option has 3 arguments, e.g. dump <segment> <format> <file>. Current supported segments are .text and .data. Also supports an address range (see m-n below). Current supported dump formats are Binary, HexText, BinaryText, AsciiText. See examples below.3.4
hexdisplay memory or register contents in hexadecimal - this is the default. (alternatives are ascii and dec)2.2
hdisplay this help. Use this option by itself and with no filename.1.0
icdisplay instruction count; the number of MIPS basic instructions 'executed'4.3
mcset memory configuration. Option has 1 argument, e.g. mc <config>. Argument <config> is case-sensitive and its possible values are Default for the default 32-bit address space, CompactDataAtZero for a 32KB address space with data segment at address 0, or CompactTextAtZero for a 32KB address space with text segment at address 0.3.7
medisplay MARS messages to standard err instead of standard out. Allows you to separate MARS messages from MIPS program output using redirection.4.3
nccopyright notice will not be displayed. Useful if redirecting or piping program output.3.5
nppseudo-instructions or extended instruction formats are not permitted.3.0
pproject option - will assemble the specified file and all other assembly files (*.asm; *.s) in its directory.3.1
senterminate MARS with exit code n if simulate (run) error occurs4.1
smstart execution at statement having global label 'main' if defined3.8
smcSelf Modifying Code - Program can write and execute in either text or data segment4.4
weassembler warnings will be considered errors.3.5
nwhere n is an integer maximum count of execution steps to simulate. If 0, negative or not specified, there is no maximum.1.0
$regwhere reg is number or name (e.g. 5, t3, f10) of register whose content to display at end of run. Even-numbered float register displays both float and double. Option may be repeated. NOTE: Depending on your command shell, you may need to escape the $, e.g. \$t32.2
reg_namewhere reg_name is the name (e.g. t3, f10) of register whose content to display at end of run. Even-numbered float register displays both float and double. Option may be repeated. $ not required.2.2
m-nmemory address range from m to n whose contents to display at end of run. m and n may be decimal or hexadecimal (starts with 0x), m <= n, both must be on word boundary. Option may be repeated.2.2
paprogram arguments - all remaining space-separated items are argument values provided to the MIPS program via $a0 (argc - argument count) and $a1 (argv - address of array containing pointers to null-terminated argument strings). The count is also at the top of the runtime stack ($sp), followed by the array.This option and its arguments must be the last items in the command!3.5

Example: java -jar mars.jar h
Displays command options and explanations.

Example: java -jar mars.jar $s0 $s1 0x10010000-0x10010010 fibonacci.asm
Assemble and run fibonacci.asm. At the end of the run, display the contents of registers $s0 and $s1, and the contents of memory locations 0x10010000 through 0x10010010. The contents are displayed in hexadecimal format.

Example: java -jar mars.jar a fibonacci.asm
Assemble fibonacci.asm. Does not attempt to run the program, and the assembled code is not saved.

Example: java -jar mars.jar 100000 infinite.asm
Assemble and run infinite.asm for a maximum of 100,000 execution steps.

Example: java -jar mars.jar p major.asm
Assemble major.asm and all other files in the same directory, link the assembled code, and run starting with the first instruction in major.asm.

Example: java -jar mars.jar major.asm minor.asm sub.asm
Assemble and link major.asm, minor.asm and sub.asm. If successful, execution will begin with the first instruction in major.asm.

Example: java -jar mars.jar a dump .text HexText hexcode.txt fibonacci.asm
Assemble fibonacci.asm without simulating (note use of 'a' option). At end of assembly, dump the text segment (machine code) to file hexcode.txt in hexadecimal text format with one instruction per line.

Example: java -jar mars.jar dump 0x10010000-0x10010020 HexText hexcode.txt fibonacci.asm
Assemble and simulate fibonacci.asm. At end of simulation, dump the contents of addresses 0x1001000 to 0x10010020 to file hexdata.txt in hexadecimal text format with one word per line.

Example: java -jar mars.jar t0 process.asm pa counter 10
Assemble and run process.asm with two program argument values, "counter" and "10". It may retrieve the argument count (2) from $a0, and the address of an array containing pointers to the strings "count" and "10", from $a1. At the end of the run, display the contents of register $t0.

The ability to run MARS from the command line is useful if you want to develop scripts (macros) to exercise a given MIPS program under multiple scenarios or if you want to run a number of different MIPS programs such as for grading purposes.

This document is available for printing on the MARS home page