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SPIM Simulator reference

The following page contains supplemental information pertaining the MIPS Instruction Set Architecture for the use of the SPIM simulator.

Quick links to supplemental information

MIPS Registers

System Services

Assembler Directives

Exception and Trap Instructions

MIPS Registers and Usage Convention

Register Name	Number	Usage
zero	0	Constant 0
at	1	Reserved for assembler
v0	2	Expression evaluation and results of a function
v1	3	Expression evaluation and results of a function
a0	4	Argument 1
a1	5	Argument 2
a2	6	Argument 3
a3	7	Argument 4
t0	8	Temporary (not preserved across call)
t1	9	Temporary (not preserved across call)
t2	10	Temporary (not preserved across call)
t3	11	Temporary (not preserved across call)
t4	12	Temporary (not preserved across call)
t5	13	Temporary (not preserved across call)
t6	14	Temporary (not preserved across call)
t7	15	Temporary (not preserved across call)
s0	16	Saved temporary (preserved across call)
s1	17	Saved temporary (preserved across call)
s2	18	Saved temporary (preserved across call)
s3	19	Saved temporary (preserved across call)
s4	20	Saved temporary (preserved across call)
s5	21	Saved temporary (preserved across call)
s6	22	Saved temporary (preserved across call)
s7	23	Saved temporary (preserved across call)
t8	24	Temporary (not preserved across call)
t9	25	Temporary (not preserved across call)
k0	26	Reserved for OS kernel
k1	27	Reserved for OS kernel
gp	28	Pointer to global area
sp	29	Stack pointer
fp	30	Frame pointer
ra	31	Return address (used by function call)

System Services

Service	System Call Code	Arguments	Result
print_int	1	$a0 = integer
print_float	2	$f12 = float
print_double	3	$f12 = double
print_string	4	$a0 = string
read_int	5		integer (in $v0)
read_float	6		float (in $f0)
read_double	7		double (in $f0)
read_string	8	$a0 = buffer, $a1 = length
sbrk	9	$a0 = amount	address (in $v0)
exit	10

Assembler Directives

.align n
Align the next datum on a 2^n byte boundary. For example, .align 2 aligns the next value on a word boundary. .align 0 turns off automatic alignment of .half, .word, .float, and .double directives until the next .data or .kdata directive.

.ascii str
Store the string in memory, but do not null-terminate it.

.asciiz str
Store the string in memory and null-terminate it.

.byte b1, ..., bn
Store the n values in successive bytes of memory.

.data
The following data items should be stored in the data segment. If the optional argument addr is present, the items are stored beginning at address addr.

.double d1, ..., dn
Store the n floating point double precision numbers in successive memory locations.

.extern sym size
Declare that the datum stored at sym is size bytes large and is a global symbol. This directive enables the assembler to store the datum in a portion of the data segment that is efficiently accessed via register $gp.

.float f1, ..., fn
Store the n floating point single precision numbers in successive memory locations.

.globl sym
Declare that symbol sym is global and can be referenced from other files.

.half h1, ..., hn
Store the n 16-bit quantities in successive memory halfwords.

.kdata
The following data items should be stored in the kernel data segment. If the optional argument addr is present, the items are stored beginning at address addr.

.ktext
The next items are put in the kernel text segment. In SPIM, these items may only be instructions or words (see the .word directive below). If the optional argument addr is present, the items are stored beginning at address addr.

.space n
Allocate n bytes of space in the current segment (which must be the data segment in SPIM).

.text
The next items are put in the user text segment. In SPIM, these items may only be instructions or words (see the .word directive below). If the optional argument addr is present, the items are stored beginning at address addr.

.word w1, ..., wn
Store the n 32-bit quantities in successive memory words.

Exception and Trap Instructions

rfe - Return From Exception
Restore the Status register.

syscall - System Call
Register v0 contains the number of the system call provided by SPIM. (see System Services above)

break n - Break
Cause exception n. Exception 1 is reserved for the debugger.

nop - No operation
Do nothing.

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