SPIM Quick Reference

Contents

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

Floating point operations can only be held by Coprocessor 1. It can operate on single precision (32bit) and double precision (64bit) floating point numbers. This coprocessor has its own register set $f0 - $f31(again 32 bit!) which you will use for float arithmetic. Because these registers are only 32bits wide, two are required to hold doubles. For simplicity: Even single precision operations only use even-numbered registers.

For passing a value from a register in one coprocessor to the other, you must use an explicit move operation! Values are moved in or out of these registers a word (32bits) 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 System Services provided by SPIM).
break n Break
Cause exception n. Exception 1 is reserved for the debugger.
nop No operation
Do nothing.