RISC-V Assembly

Read and write RISC-V assembly, from your first instruction up to functions and memory. It ships with a simulator that runs in the browser.

Open in Lux Simulator

Lessons

What is assembly?Doing mathInput & outputDecisions & loopsFunctions & the stackMemory: load & store

Reference

Arithmetic

add
Add two registers together.
sub
Subtract one register from another.
addi
Add a small constant to a register.
mul
Multiply, keeping the low 32 bits.
mulh
High 32 bits of a signed product.
div
Signed integer division.
divu
Unsigned integer division.
rem
Signed remainder (modulo).
remu
Unsigned remainder.
neg
Flip the sign of a number.

Bitwise logic

and
Bitwise AND of two registers.
or
Bitwise OR of two registers.
xor
Bitwise exclusive-OR.
andi
AND with a constant.
ori
OR with a constant.
xori
XOR with a constant.
not
Flip every bit.

Shifts

sll
Shift bits left (by a register).
srl
Shift bits right, zero-filled.
sra
Shift right, keeping the sign.
slli
Shift left by a fixed amount.
srli
Shift right by a constant, zero-filled.
srai
Shift right by a constant, sign-kept.

Compare & set

slt
Set to 1 if less than (signed).
sltu
Set if less than (unsigned).
slti
Set if less than a constant (signed).
sltiu
Set if less than a constant (unsigned).
seqz
Set to 1 if the value is zero.
snez
Set to 1 if the value is non-zero.

Memory

lw
Load a 32-bit word from memory.
lh
Load a 16-bit halfword (signed).
lb
Load one byte (signed).
lhu
Load a 16-bit halfword (unsigned).
lbu
Load one byte (unsigned).
sw
Store a 32-bit word to memory.
sh
Store the low 16 bits.
sb
Store the low 8 bits.
la
Load the address of a label.
li
Load any constant into a register.
mv
Copy one register to another.

Branches

beq
Jump if two registers are equal.
bne
Jump if two registers differ.
blt
Jump if less than (signed).
bge
Jump if greater or equal (signed).
bltu
Jump if less than (unsigned).
bgeu
Jump if greater or equal (unsigned).
beqz
Jump if the register is zero.
bnez
Jump if the register is non-zero.
bgt
Jump if greater than (signed).
ble
Jump if less or equal (signed).

Jumps & functions

jal
Call: jump and save the return spot.
jalr
Jump to a computed address, and link.
j
Jump unconditionally.
jr
Jump to an address in a register.
call
Call a function.
ret
Return from a function.
lui
Load a constant into the upper bits.
auipc
Add an upper constant to the PC.

System

ecall
Ask the system to do something.
nop
Do nothing for one instruction.