SPIM Quick Reference

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MIPS Registers and Usage Convention
Table of sycsalls
Assembler Directives
SPIM Instruction Set

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.

SPIM Instruction Set

Arithmetic and Logical Instructions

In all instructions below, Src2 can either be a register or an immediate value (a 16 bit integer). The immediate forms of the instructions are only included for reference. The assembler will translate the more general form of an instruction (e.g., add) into the immediate form (e.g., addi) if the second argument is constant.

`abs Rdest, Rsrc`	Absolute Value
Put the absolute value of the integer from register `Rsrc` in register `Rdest`.
`add Rdest, Rsrc1, Src2`	Addition (with overflow)
`addi Rdest, Rsrc1, Imm`	Addition Immediate (with overflow)
`addu Rdest, Rsrc1, Src2`	Addition (without overflow)
`addiu Rdest, Rsrc1, Imm`	Addition Immediate (without overflow)
Put the sum of the integers from register `Rsrc1` and `Src2` (or `Imm`) into register `Rdest`.
`and Rdest, Rsrc1, Src2`	AND
`andi Rdest, Rsrc1, Imm`	AND Immediate
Put the logical AND of the integers from register `Rsrc1` and `Src2` (or `Imm`) into register `Rdest`.
`div Rsrc1, Rsrc2`	Divide (with overflow)
`divu Rsrc1, Rsrc2`	Divide (without overflow)
Divide the contents of the two registers. Leave the quotient in register `lo` and the remainder in register `hi`. Note that if an operand is negative, the remainder is unspecified by the MIPS architecture and depends on the conventions of the machine on which SPIM is run.
`div Rdest, Rsrc1, Src2`	Divide (with overflow)
`divu Rdest, Rsrc1, Src2`	Divide (without overflow)
Put the quotient of the integers from register `Rsrc1` and `Src2` into register `Rdest`.
`mul Rdest, Rsrc1, Src2`	Multiply (without overflow)
`mulo Rdest, Rsrc1, Src2`	Multiply (with overflow)
`mulou Rdest, Rsrc1, Src2`	Unsigned Multiply (with overflow)
Put the product of the integers from register `Rsrc1` and `Src2` into register `Rdest`.
`mult Rsrc1, Rsrc2`	Multiply
`multu Rsrc1, Rsrc2`	Unsigned Multiply
Multiply the contents of the two registers. Leave the low-order word of the product in register `lo` and the high-word in register `hi`.
`neg Rdest, Rsrc`	Negate Value (with overflow)
`negu Rdest, Rsrc`	Negate Value (without overflow)
Put the negative of the integer from register `Rsrc` into register `Rdest`.
`nor Rdest, Rsrc1, Src2`	NOR
Put the logical NOR of the integers from register `Rsrc1` and `Src2` into register `Rdest`.
`not Rdest, Rsrc`	NOT
Put the bitwise logical negation of the integer from register `Rsrc` into register `Rdest`.
`or Rdest, Rsrc1, Src2`	OR
`ori Rdest, Rsrc1, Imm`	OR Immediate
Put the logical OR of the integers from register `Rsrc1` and `Src2` (or `Imm`) into register `Rdest`.
`rem Rdest, Rsrc1, Src2`	Remainder
`remu Rdest, Rsrc1, Src2`	Unsigned Remainder
Put the remainder from dividing the integer in register `Rsrc1` by the integer in `Src2` into register `Rdest`. Note that if an operand is negative, the remainder is unspecified by the MIPS architecture and depends on the conventions of the machine on which SPIM is run.
`rol Rdest, Rsrc1, Src2`	Rotate Left
`ror Rdest, Rsrc1, Src2`	Rotate Right
Rotate the contents of register `Rsrc1` left (right) by the distance indicated by `Src2` and put the result in register `Rdest`.
`sll Rdest, Rsrc1, Src2`	Shift Left Logical
`sllv Rdest, Rsrc1, Rsrc2`	Shift Left Logical Variable
`sra Rdest, Rsrc1, Src2`	Shift Right Arithmetic
`srav Rdest, Rsrc1, Rsrc2`	Shift Right Arithmetic Variable
`srl Rdest, Rsrc1, Src2`	Shift Right Logical
`srlv Rdest, Rsrc1, Rsrc2`	Shift Right Logical Variable
Shift the contents of register `Rsrc1` left (right) by the distance indicated by `Src2` (`Rsrc2`) and put the result in register `Rdest`.
`sub Rdest, Rsrc1, Src2`	Subtract (with overflow)
`subu Rdest, Rsrc1, Src2`	Subtract (without overflow)
Put the difference of the integers from register `Rsrc1` and `Src2` into register `Rdest`.
`xor Rdest, Rsrc1, Src2`	XOR
`xori Rdest, Rsrc1, Imm`	XOR Immediate
Put the logical XOR of the integers from register `Rsrc1` and `Src2` (or `Imm`) into register `Rdest`.

Constant-Manipulating Instructions

`li Rdest, imm`	Load Immediate
Move the immediate `imm` into register `Rdest`.
`lui Rdest, imm`	Load Upper Immediate
Load the lower halfword of the immediate `imm` into the upper halfword of register `Rdest`. The lower bits of the register are set to 0.

Comparison Instructions

In all instructions below, Src2 can either be a register or an immediate value (a 16 bit integer).

`seq Rdest, Rsrc1, Src2`	Set Equal
Set register `Rdest` to 1 if register `Rsrc1` equals `Src2` and to be 0 otherwise.
`sge Rdest, Rsrc1, Src2`	Set Greater Than Equal
`sgeu Rdest, Rsrc1, Src2`	Set Greater Than Equal Unsigned
Set register `Rdest` to 1 if register `Rsrc1` is greater than or equal to `Src2` and to 0 otherwise.
`sgt Rdest, Rsrc1, Src2`	Set Greater Than
`sgtu Rdest, Rsrc1, Src2`	Set Greater Than Unsigned
Set register `Rdest` to 1 if register `Rsrc1` is greater than `Src2` and to 0 otherwise.
`sle Rdest, Rsrc1, Src2`	Set Less Than Equal
`sleu Rdest, Rsrc1, Src2`	Set Less Than Equal Unsigned
Set register `Rdest` to 1 if register `Rsrc1` is less than or equal to `Src2` and to 0 otherwise.
`slt Rdest, Rsrc1, Src2`	Set Less Than
`slti Rdest, Rsrc1, Imm`	Set Less Than Immediate
`sltu Rdest, Rsrc1, Src2`	Set Less Than Unsigned
`sltiu Rdest, Rsrc1, Imm`	Set Less Than Unsigned Immediate
Set register `Rdest` to 1 if register `Rsrc1` is less than `Src2` (or `Imm`) and to 0 otherwise.
`sne Rdest, Rsrc1, Src2`	Set Not Equal
Set register `Rdest` to 1 if register `Rsrc1` is not equal to `Src2` and to 0 otherwise.

Branch and Jump Instructions

In all instructions below, Src2 can either be a register or an immediate value (integer). Branch instructions use a signed 16-bit offset field; hence they can jump 2^15-1 instructions (not bytes) forward or 2^15 instructions backwards. The jump instruction contains a 26 bit address field.

`b label`	Branch instruction
Unconditionally branch to the instruction at the label.
`bczt label`	Branch Coprocessor z True
`bczf label`	Branch Coprocessor z False
Conditionally branch to the instruction at the label if coprocessor z's condition flag is true (false).
`beq Rsrc1, Src2, label`	Branch on Equal
Conditionally branch to the instruction at the label if the contents of register `Rsrc1` equals `Src2`.
`beqz Rsrc, label`	Branch on Equal Zero
Conditionally branch to the instruction at the label if the contents of `Rsrc` equals 0.
`bge Rsrc1, Src2, label`	Branch on Greater Than Equal
`bgeu Rsrc1, Src2, label`	Branch on GTE Unsigned
Conditionally branch to the instruction at the label if the contents of register `Rsrc1` are greater than or equal to `Src2`.
`bgez Rsrc, label`	Branch on Greater Than Equal Zero
Conditionally branch to the instruction at the label if the contents of `Rsrc` are greater than or equal to 0.
`bgezal Rsrc, label`	Branch on Greater Than Equal Zero And Link
Conditionally branch to the instruction at the label if the contents of `Rsrc` are greater than or equal to 0. Save the address of the next instruction in register 31.
`bgt Rsrc1, Src2, label`	Branch on Greater Than
`bgtu Rsrc1, Src2, label`	Branch on Greater Than Unsigned
Conditionally branch to the instruction at the label if the contents of register `Rsrc1` are greater than `Src2`.
`bgtz Rsrc, label`	Branch on Greater Than Zero
Conditionally branch to the instruction at the label if the contents of `Rsrc` are greater than 0.
`ble Rsrc1, Src2, label`	Branch on Less Than Equal
`bleu Rsrc1, Src2, label`	Branch on LTE Unsigned
Conditionally branch to the instruction at the label if the contents of register `Rsrc1` are less than or equal to `Src2`.
`blez Rsrc, label`	Branch on Less Than Equal Zero
Conditionally branch to the instruction at the label if the contents of `Rsrc` are less than or equal to 0.
`bgezal Rsrc, label`	Branch on Greater Than Equal Zero And Link
`bltzal Rsrc, label`	Branch on Less Than And Link
Conditionally branch to the instruction at the label if the contents of `Rsrc` are greater or equal to 0 or less than 0, respectively. Save the address of the next instruction in register 31.
`blt Rsrc1, Src2, label`	Branch on Less Than
`bltu Rsrc1, Src2, label`	Branch on Less Than Unsigned
Conditionally branch to the instruction at the label if the contents of register `Rsrc1` are less than `Src2`.
`bltz Rsrc, label`	Branch on Less Than Zero
Conditionally branch to the instruction at the label if the contents of `Rsrc` are less than 0.
`bne Rsrc1, Src2, label`	Branch on Not Equal
Conditionally branch to the instruction at the label if the contents of register `Rsrc1` are not equal to `Src2`.
`bnez Rsrc, label`	Branch on Not Equal Zero
Conditionally branch to the instruction at the label if the contents of `Rsrc` are not equal to 0.
`j label`	Jump
Unconditionally jump to the instruction at the label.
`jal label`	Jump and Link
`jalr Rsrc`	Jump and Link Register
Unconditionally jump to the instruction at the label or whose address is in register `Rsrc`. Save the address of the next instruction in register 31.
`jr Rsrc`	Jump Register
Unconditionally jump to the instruction whose address is in register `Rsrc`.

Load Instructions

`la Rdest, address`	Load Address
Load computed address, not the contents of the location, into register `Rdest`.
`lb Rdest, address`	Load Byte
`lbu Rdest, address`	Load Unsigned Byte
Load the byte at address into register `Rdest`. The byte is sign-extended by the `lb`, but not the `lbu`, instruction.
`ld Rdest, address`	Load Double-Word
Load the 64-bit quantity at address into registers `Rdest` and `Rdest + 1`.
`lh Rdest, address`	Load Halfword
`lhu Rdest, address`	Load Unsigned Halfword
Load the 16-bit quantity (halfword) at address into register `Rdest`. The halfword is sign-extended by the `lh`, but not the `lhu`, instruction
`lw Rdest, address`	Load Word
Load the 32-bit quantity (word) at address into register `Rdest`.
`lwcz Rdest, address`	Load Word Coprocessor z
Load the word at address into register `Rdest` of coprocessor z (0-3).
`lwl Rdest, address`	Load Word Left
`lwr Rdest, address`	Load Word Right
Load the left (right) bytes from the word at the possibly-unaligned address into register `Rdest`.
`ulh Rdest, address`	Unaligned Load Halfword
`ulhu Rdest, address`	Unaligned Load Halfword Unsigned
Load the 16-bit quantity (halfword) at the possibly-unaligned address into register `Rdest`. The halfword is sign-extended by the `ulh`, but not the `ulhu`, instruction
`ulw Rdest, address`	Unaligned Load Word
Load the 32-bit quantity (word) at the possibly-unaligned address into register `Rdest`.

Store Instructions

`sb Rsrc, address`	Store Byte
Store the low byte from register `Rsrc` at address.
`sd Rsrc, address`	Store Double-Word
Store the 64-bit quantity in registers `Rsrc` and `Rsrc + 1` at address.
`sh Rsrc, address`	Store Halfword
Store the low halfword from register `Rsrc` at address.
`sw Rsrc, address`	Store Word
S tore the word from register `Rsrc` at address.
`swcz Rsrc, address`	Store Word Coprocessor z
Store the word from register `Rsrc` of coprocessor z at address.
`swl Rsrc, address`	Store Word Left
`swr Rsrc, address`	Store Word Right
Store the left (right) bytes from register `Rsrc` at the possibly-unaligned address.
`ush Rsrc, address`	Unaligned Store Halfword
Store the low halfword from register `Rsrc` at the possibly-unaligned address.
`usw Rsrc, address`	Unaligned Store Word
Store the word from register `Rsrc` at the possibly-unaligned address.

Data Movement Instructions

`move Rdest, Rsrc`	Move
Move the contents of `Rsrc` to `Rdest`. The multiply and divide unit produces its result in two additional registers, hi and lo. These instructions move values to and from these registers. The multiply, divide, and remainder instructions described above are pseudoinstructions that make it appear as if this unit operates on the general registers and detect error conditions such as divide by zero or overflow.
`mfhi Rdest`	Move From hi
`mflo Rdest`	Move From lo
Move the contents of the hi (lo) register to register `Rdest`.
`mthi Rdest`	Move To hi
`mtlo Rdest`	Move To lo
Move the contents register `Rdest` to the hi (lo) register. Coprocessors have their own register sets. These instructions move values between these registers and the CPU's registers.
`mfcz Rdest, CPsrc`	Move From Coprocessor z
Move the contents of coprocessor z's register `CPsrc` to CPU register `Rdest`.
`mfc1.d Rdest, FRsrc1`	Move Double From Coprocessor 1
Move the contents of floating point registers `FRsrc1` and `FRsrc1 + 1` to CPU registers `Rdest` and `Rdest + 1`.
`mtcz Rsrc, CPdest`	Move To Coprocessor z
Move the contents of CPU register `Rsrc` to coprocessor z's register `CPdest`.

Floating Point Instructions

The MIPS has a floating point coprocessor (numbered 1) that operates on single precision (32-bit) and double precision (64-bit) floating point numbers. This coprocessor has its own registers, which are numbered f0-f31. Because these registers are only 32-bits wide, two of them are required to hold doubles. To simplify matters, floating point operations only use even-numbered registers - including instructions that operate on single floats. Values are moved in or out of these registers a word (32-bits) at a time by lwc1, swc1, mtc1, and mfc1 instructions described above or by the l.s, l.d, s.s, and s.d pseudoinstructions described below. The flag set by floating point comparison operations is read by the CPU with its bc1t and bc1f instructions. In all instructions below, FRdest, FRsrc1, FRsrc2, and FRsrc are floating point registers (e.g., f2).

`abs.d FRdest, FRsrc`	Floating Point Absolute Value Double
`abs.s FRdest, FRsrc`	Floating Point Absolute Value Single
Compute the absolute value of the floating float double (single) in register `FRsrc` and put it in register `FRdest`.
`add.d FRdest, FRsrc1, FRsrc2`	Floating Point Addition Double
`add.s FRdest, FRsrc1, FRsrc2`	Floating Point Addition Single
Compute the sum of the floating float doubles (singles) in registers `FRsrc1` and `FRsrc2` and put it in register `FRdest`.
`c.eq.d FRsrc1, FRsrc2`	Compare Equal Double
`c.eq.s FRsrc1, FRsrc2`	Compare Equal Single
Compare the floating point double in register `FRsrc1` against the one in `FRsrc2` and set the floating point condition flag true if they are equal.
`c.le.d FRsrc1, FRsrc2`	Compare Less Than Equal Double
`c.le.s FRsrc1, FRsrc2`	Compare Less Than Equal Single
Compare the floating point double in register `FRsrc1` against the one in `FRsrc2` and set the floating point condition flag true if the first is less than or equal to the second.
`c.lt.d FRsrc1, FRsrc2`	Compare Less Than Double
`c.lt.s FRsrc1, FRsrc2`	Compare Less Than Single
Compare the floating point double in register `FRsrc1` against the one in `FRsrc2` and set the condition flag true if the first is less than the second.
`cvt.d.s FRdest, FRsrc`	Convert Single to Double
`cvt.d.w FRdest, FRsrc`	Convert Integer to Double
Convert the single precision floating point number or integer in register `FRsrc` to a double precision number and put it in register `FRdest`.
`cvt.s.d FRdest, FRsrc`	Convert Double to Single
`cvt.s.w FRdest, FRsrc`	Convert Integer to Single
Convert the double precision floating point number or integer in register `FRsrc` to a single precision number and put it in register `FRdest`.
`cvt.w.d FRdest, FRsrc`	Convert Double to Integer
`cvt.w.s FRdest, FRsrc`	Convert Single to Integer
Convert the double or single precision floating point number in register `FRsrc` to an integer and put it in register `FRdest`.
`div.d FRdest, FRsrc1, FRsrc2`	Floating Point Divide Double
`div.s FRdest, FRsrc1, FRsrc2`	Floating Point Divide Single
Compute the quotient of the floating float doubles (singles) in registers `FRsrc1` and `FRsrc2` and put it in register `FRdest`.
`l.d FRdest, address`	Load Floating Point Double
`l.s FRdest, address`	Load Floating Point Single
Load the floating float double (single) at `address` into register `FRdest`.
`mov.d FRdest, FRsrc`	Move Floating Point Double
`mov.s FRdest, FRsrc`	Move Floating Point Single
Move the floating float double (single) from register `FRsrc` to register `FRdest`.
`mul.d FRdest, FRsrc1, FRsrc2`	Floating Point Multiply Double
`mul.s FRdest, FRsrc1, FRsrc2`	Floating Point Multiply Single
Compute the product of the floating float doubles (singles) in registers `FRsrc1` and `FRsrc2` and put it in register `FRdest`.
`neg.d FRdest, FRsrc`	Negate Double
`neg.s FRdest, FRsrc`	Negate Single
Negate the floating point double (single) in register `FRsrc` and put it in register `FRdest`.
`s.d FRdest, address`	Store Floating Point Double
`s.s FRdest, address`	Store Floating Point Single
Store the floating float double (single) in register `FRdest` at `address`.
`sub.d FRdest, FRsrc1, FRsrc2`	Floating Point Subtract Double
`sub.s FRdest, FRsrc1, FRsrc2`	Floating Point Subtract Single
Compute the difference of the floating float doubles (singles) in registers `FRsrc1` and `FRsrc2` and put it in register `FRdest`.

Exception and Trap Instructions

`rfe`	Return From Exception
Restore the Status register.
`syscall`	System Call
Register `v0` contains the number of the system call (see