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Manual Reference Pages  -  XSPIM (1)


xspim - A MIPS32 Simulator




xspim [-asm/-bare
-stext size
        -sdata size
        -sstack size
        -sktext size
        -skdata size
        -ldata size
        -lstack size
        -lkdata size
-file file -execute file


SPIM S20 is a simulator that runs programs for the MIPS32 RISC computers. SPIM can read and immediately execute files containing assembly language or MIPS executable files. SPIM is a self-contained system for running these programs and contains a debugger and interface to a few operating system services.

SPIM comes in two versions. The plain version is called spim. It runs on any type of terminal. It operates like most programs of this type: you type a line of text, hit the return key, and spim executes your command. The fancier version of SPIM is called xspim. It uses the X-window system, so you must have a bit-mapped display to run it. xspim, however, is a much easier program to learn and use because its commands are always visible on the screen and because it continually displays the machine’s registers.


xspim has many options:

-asm Simulate the virtual MIPS machine provided by the assembler. This is the default.

-bare Simulate a bare MIPS machine without pseudo-instructions or the additional addressing modes provided by the assembler. Implies -quiet.

-exception Load the standard exception handler and startup code. This is the default.

-noexception Do not load the standard exception handler and startup code. This exception handler handles exceptions. When an exception occurs, SPIM jumps to location 0x80000080, which must contain code to service the exception. In addition, this file contains startup code that invokes the routine main. Without the startup routine, SPIM begins execution at the instruction labeled __start.

-quiet Print a message when an exception occurs. This is the default.

-noquiet Do not print a message at exceptions.

-mapped_io Enable the memory-mapped IO facility. Programs that use SPIM syscalls to read from the terminal cannot also use memory-mapped IO.

-nomapped_io Disable the memory-mapped IO facility.

-delayed_branches Simulate MIPS’s delayed control transfers by executing the instruction after a branch, jump, or call before transferring control. SPIM’s default is to simulate non-delayed transfers, unless the -bare flag is set.

-delayed_loads Simulate MIPS’s original, non-interlocked load instructions. SPIM’s default is to simulate non-delayed loads, unless the -bare flag is set.

-stext size -sdata size -sstack size -sktext size -skdata size Sets the initial size of memory segment seg to be size bytes. The memory segments are named: text, data, stack, ktext, and kdata. The text segment contains instructions from a program. The data segment holds the program’s data. The stack segment holds its runtime stack. In addition to running a program, SPIM also executes system code that handles interrupts and exceptions. This code resides in a separate part of the address space called the kernel. The ktext segment holds this code’s instructions and kdata holds its data. There is no kstack segment since the system code uses the same stack as the program. For example, the pair of arguments -sdata 2000000 starts the user data segment at 2,000,000 bytes.

-ldata size -lstack size -lkdata size Sets the limit on how large memory segment seg can grow to be size bytes. The memory segments that can grow are data, stack, and kdata.

-hexgpr Disply the general purpose registers (GPRs) in hexadecimal.

-nohexgpr Disply the general purpose registers (GPRs) in decimal.

-hexfpr Disply the floating-point registers (FPRs) in hexadecimal.

-nohexfpr Disply the floating-point registers (FPRs) as floating-point values

-file file 10 Load and execute the assembly code in the file.

-execute file 10 Load and execute the MIPS executable (a.out) file. Only works on systems using a MIPS processors.


Instruction opcodes cannot be used as labels.


James R. Larus, ‘‘SPIM S20: A MIPS R2000 Simulator,’’ included with SPIM distribution.


James R. Larus, Computer Sciences Department, University of Wisconsin-Madison. Current address: James R Larus (, Microsoft Research.
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