RISC-V ISA Reference

Instruction Encoding Templates

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R-type funct7 rs2 rs1 funct3 rd opcode
I-type imm[11:0]
S-Type imm[11:5] rs2 imm[4:0]
B-type imm[12|10:5] imm [4:1|11]
J-type imm[20|10:1|11|19:12] rd
U-type imm[31:12]

RV32I Base Integer Instruction Set

Arithmetic Instructions

Instruction Name Description Opcode Funct3 Funct7
R-type add rd, rs1, rs2 add R[rd] = R[rs1] + R[rs2] 011 0011 000 000 0000
sub rd, rs1, rs2 subtract R[rd] = R[rs1] - R[rs2] 011 0011 000 010 0000
and rd, rs1, rs2 bitwise and R[rd] = R[rs1] & R[rs2] 011 0011 111 000 0000
or rd, rs1, rs2 bitwise or R[rd] = R[rs1] | R[rs2] 011 0011 110 000 0000
xor rd, rs1, rs2 bitwise xor R[rd] = R[rs1] ^ R[rs2] 011 0011 100 000 0000
sll rd, rs1, rs2 shift left logical R[rd] = R[rs1] << R[rs2] 011 0011 001 000 0000
srl rd, rs1, rs2 shift right logical R[rd] = R[rs1] >> R[rs2]
(zero-extend)		 011 0011 101 000 0000
sra rd, rs1, rs2 shift right arithmetic R[rd] = R[rs1] >> R[rs2]
(sign-extend)		 011 0011 101 010 0000
slt rd, rs1, rs2 set less than (signed) if (R[rs1] < R[rs2]) { R[rd] = 1; } else { R[rd] = 0; } 011 0011 010 000 0000
sltu rd, rs1, rs2 set less than (unsigned) 011 0011 011 000 0000
I-type addi rd, rs1, imm add immediate R[rd] = R[rs1] + imm(sign-extend imm) 001 0011 000 n/a
andi rd, rs1, imm bitwise and immediate R[rd] = R[rs1] & imm(sign-extend imm) 001 0011 111 n/a
ori rd, rs1, imm bitwise or immediate R[rd] = R[rs1] | imm(sign-extend imm) 001 0011 110 n/a
xori rd, rs1, imm bitwise xor immediate R[rd] = R[rs1] ^ imm(sign-extend imm) 001 0011 100 n/a
slti rd, rs1, imm set less than immediate (signed) if (R[rs1] < imm) { R[rd] = 1; } else { R[rd] = 0; }(sign-extend imm) 001 0011 010 n/a
sltiu rd, rs1, imm set less than immediate (unsigned) 001 0011 011 n/a
slli rd, rs1, imm shift left logical immediate R[rd] = R[rs1] << imm[4:0] 001 0011 001 000 0000
srli rd, rs1, imm shift right logical immediate R[rd] = R[rs1] >> imm[4:0]
(zero-extend)		 001 0011 101 000 0000
srai rd, rs1, imm shift right arithmetic immediate R[rd] = R[rs1] >> imm[4:0]
(sign-extend)		 001 0011 101 010 0000

Memory Instructions

Instruction Name Description Opcode Funct3
I-type lb rd, imm(rs1) load byte R[rd] = M[R[rs1] + imm][7:0]
(sign-extend)		 000 0011 000
lbu rd, imm(rs1) load byte (unsigned) R[rd] = M[R[rs1] + imm][7:0]
(zero-extend)		 000 0011 100
lh rd, imm(rs1) load half-word R[rd] = M[R[rs1] + imm][15:0]
(sign-extend)		 000 0011 001
lhu rd, imm(rs1) load half-word (unsigned) R[rd] = M[R[rs1] + imm][15:0]
(zero-extend)		 000 0011 101
lw rd, imm(rs1) load word R[rd] = M[R[rs1] + imm][31:0]
(sign-extend in RV64I)		 000 0011 010
S-Type sb rs2, imm(rs1) store byte M[R[rs1] + imm][7:0] = R[rs2][7:0] 010 0011 000
sh rs2, imm(rs1) store half-word M[R[rs1] + imm][15:0] = R[rs2][15:0] 010 0011 001
sw rs2, imm(rs1) store word M[R[rs1] + imm][31:0] = R[rs2][31:0] 010 0011 010

Control Instructions

Instruction Name Description Opcode Funct3
B-type beq rs1, rs2, label branch if equal if (R[rs1] == R[rs2]) { PC = PC + offset } 110 0011 000
bne rs1, rs2, label branch if not equal if (R[rs1] != R[rs2]) { PC = PC + offset } 110 0011 001
blt rs1, rs2, label branch if less than (signed) if (R[rs1] < R[rs2]) { PC = PC + offset } 110 0011 100
bltu rs1, rs2, label branch if less than (unsigned) 110 0011 110
bge rs1, rs2, label branch if greater or equal (signed) if (R[rs1] >= R[rs2]) { PC = PC + offset } 110 0011 101
bgeu rs1, rs2, label branch if greater or equal (unsigned) 110 0011 111
J-type jal rd, label jump and link R[rd] = PC + 4 PC = PC + offset 110 1111 n/a
I-type jalr rd, rs1, label jump and link register R[rd] = PC + 4 PC = R[rs1] + imm 110 0111 000

Other Instructions

Instruction Name Description Opcode Funct3
U-type auipc rd, immu add upper immediate to PC R[rd] = PC + imm << 12(sign-extend shifted immediate) 011 0111 n/a
lui rd, immu load upper immediate R[rd] = imm << 12(sign-extend shifted immediate) 011 0111 n/a
I-type ebreak environment BREAK asks the debugger to do something (imm=0) 111 0011 000
ecall environment ECALL asks the OS to do something (imm=1) 111 0011 000

RV32A/RV64A Standard Extension for Atomic Instructions (partial list)

Info

The following table lists the load-reserved and store-conditional instructions that are available for RV32 and RV64. For documentation of the atomic memory operations (amo) see the RISC-V Instruction Set Manual, Vol. 1, Chapter 9.4

Instruction Name Opcode Funct3 Funct7
R-type lr.w rd, rs1, rs2 load reserved word 010 1111 010 00010 | aq | rl
lr.d rd, rs1, rs2 load reserved double-word (RV64 only) 010 1111 011 00010 | aq | rl
sc.w rd, rs1, rs2 store conditional word 010 1111 010 00011 | aq | rl
sc.d rd, rs1, rs2 store conditional double-word (RV64 only) 010 1111 011 00011 | aq | rl

RV64I Base Integer Instruction Set (in addition to RV32I)

Info

The 15 instructions in the RV64I set build on the RV32I variants by providing support for 64-bit load/store operations and extensions of operations on 32-bit values and results. There is a more detailed discussion of the problems that arise in extension in the class notes.

Instruction Name Description Opcode Funct3 Funct7
R-type addw rd, rs1, rs2 add word R[rd] = (R[rs1][31:0] + R[rs2][31:0])[31:0]
(sign-extend)		 011 1011 000 000 0000
subw rd, rs1, rs2 subtract word R[rd] = (R[rs1][31:0] - R[rs2][31:0])[31:0]
(sign-extend)		 011 1011 000 010 0000
sllw rd, rs1, rs2 shift left logical word R[rd] = (R[rs1][31:0] << R[rs2])[31:0]
(sign-extend)		 011 1011 001 000 0000
srlw rd, rs1, rs2 shift right logical word R[rd] = (R[rs1][31:0] >> R[rs2])[31:0]
(zero-extend)		 011 1011 101 000 0000
sraw rd, rs1, rs2 shift right arithmetic word R[rd] = (R[rs1][31:0] >> R[rs2])[31:0]
(sign-extend)		 011 1011 101 010 0000
I-type slli rd, rs1, imm shift left logical immediate R[rd] = R[rs1] << imm[5:0] 001 0011 001 n/a
srli rd, rs1, imm shift right logical immediate R[rd] = R[rs1] >> imm[5:0]
(zero-extend)		 001 0011 101 n/a
srai rd, rs1, imm shift right arithmetic immediate R[rd] = R[rs1] >> imm[5:0]
(sign-extend)		 001 0011 101 n/a
addiw rd, rs1, imm add immediate word R[rd] = (R[rs1] + imm)[31:0]
(sign-extend imm and result)		 001 1011 000 n/a
slliw rd, rs1, imm shift left logical immediate word R[rd] = (R[rs1][31:0] << imm)[31:0]
(sign-extend)		 001 1011 001 000 0000
srliw rd, rs1, imm shift right logical immediate word R[rd] = (R[rs1][31:0] >> imm)[31:0]
(zero-extend)		 001 1011 101 000 0000
sraiw rd, rs1, imm shift right arithmetic immediate word R[rd] = (R[rs1][31:0] >> imm)[31:0]
(sign-extend)		 001 1011 101 010 0000
Load/Store
(I-type/S-type)		 lwu rd, imm(rs1) load word (unsigned) R[rd] = M[R[rs1] + imm][31:0]
(zero-extend)		 000 0011 110 n/a
ld rd, imm(rs1) load double word R[rd] = M[R[rs1] + imm] 000 0011 011 n/a
sd rs2, imm(rs1) store double word M[R[rs1] + imm] = R[rs2] 010 0011 011 n/a

Standard Extension for Integer Multiplication and Division (RV32M and RV64M)

Let XLEN = the width of an integer register in bits.

Instruction Name Description Opcode Funct3 Funct7
RV32M
(R-type)		 mul rd, rs1, rs2 multiply R[rd] = R[rs1] * R[rs2]
 011 0011 000 000 0001
mulh rd, rs1, rs2 multiply upper half R[rd] = (R[rs1] * R[rs2])[(2×XLEN-1):XLEN]
(R[rs1] and R[rs2] signed) 		011 0011 001 000 0001
mulhu rd, rs1, rs2 multiply upper half unsigned R[rd] = (R[rs1] * R[rs2])[(2×XLEN-1):XLEN]
(R[rs1] and R[rs2] unsigned)		 011 0011 011 000 0001
mulhsu rd, rs1, rs2 multiply upper half signed × unsigned R[rd] = (R[rs1] * R[rs2])[(2×XLEN-1):XLEN]
(signed R[rs1] and unsigned R[rs2])		 011 0011 010 000 0001
div rd, rs1, rs2 quotient (signed) R[rd] = R[rs2] == 0 ? -1 : R[rs1] / R[rs2]
(R[rs1] and R[rs2] signed, the quotient of a signed division with overflow is equal to the dividend)		 011 0011 100 000 0001
divu rd, rs1, rs2 quotient (unsigned) R[rd] = R[rs2] == 0 ? -1 : R[rs1] / R[rs2]
(R[rs1] and R[rs2] unsigned)		 011 0011 101 000 0001
rem rd, rs1, rs2 remainder (signed) R[rd] = R[rs2] == 0 ? R[rs1] : R[rs1] % R[rs2]
(R[rs1] and R[rs2] signed)		 011 0011 110 000 0001
remu rd, rs1, rs2 remainder (unsigned) R[rd] = R[rs2] == 0 ? R[rs1] : R[rs1] % R[rs2]
(R[rs1] and R[rs2] unsigned)		 011 0011 111 000 0001
RV64M
(R-type)		 mulw rd, rs1, rs2 multiply word R[rd] = R[rs1][31:0] * R[rs2][31:0]
(sign-extend)		 011 1011 000 000 0001
divw rd, rs1, rs2 quotient (signed) word R[rd] = R[rs2][31:0] == 0 ? -1 : R[rs1][31:0] / R[rs2][31:0]
(R[rs1][31:0] and R[rs2][31:0] signed, result is sign-extended, the quotient of a signed division with overflow is equal to the dividend)		 011 1011 100 000 0001
divuw rd, rs1, rs2 quotient (unsigned) word R[rd] = R[rs2][31:0] == 0 ? -1 : R[rs1][31:0] / R[rs2][31:0]
(R[rs1][31:0] and R[rs2][31:0] unsigned, result is sign-extended)		 011 1011 101 000 0001
remw rd, rs1, rs2 remainder (signed) word R[rd] = R[rs2][31:0] == 0 ? R[rs1][31:0] : R[rs1][31:0] % R[rs2][31:0]
(R[rs1][31:0] and R[rs2][31:0] signed, result is sign-extended)		 011 1011 110 000 0001
remuw rd, rs1, rs2 remainder (unsigned) word R[rd] = R[rs2][31:0] == 0 ? R[rs1][31:0] : R[rs1][31:0] % R[rs2][31:0]
(R[rs1][31:0] and R[rs2][31:0] unsigned, result is sign-extended)		 011 1011 111 000 0001