[RISC-V]Standard Extensions

RISC-V has standardized a series of standard extensions beyond the integer base instructions which can be implemented or omitted as desired depending on the design goals (e.g. energy/area/performance/storage goals).

Overview

By default, only the core ISA must be implemented presenting great opportunity for area and energy optimization. However, additional functionality is sometimes desired. RISC-V comes with a series of standard extensions that enable additional functionality beyond the core ISA such as floating point and operations and bit manipulation. Extensions can be implemented and omitted as desired. Those extensions are:

Name	Description	Version	Status	Instruction Count
RV32I	Base Integer Instruction Set - 32-bit	2.1	Frozen	49
RV32E	Base Integer Instruction Set (embedded) - 32-bit, 16 registers	1.9	Open	Same as RV32I
RV64I	Base Integer Instruction Set - 64-bit	2.0	Frozen	14
RV128I	Base Integer Instruction Set - 128-bit	1.7	Open	14
Extension
M	Standard Extension for Integer Multiplication and Division	2.0	Frozen	8
A	Standard Extension for Atomic Instructions	2.0	Frozen	11
F	Standard Extension for Single-Precision Floating-Point	2.0	Frozen	25
D	Standard Extension for Double-Precision Floating-Point	2.0	Frozen	25
G	Shorthand for the base and above extensions	n/a	n/a	n/a
Q	Standard Extension for Quad-Precision Floating-Point	2.0	Frozen	27
L	Standard Extension for Decimal Floating-Point	0.0	Open	Undefined Yet
C	Standard Extension for Compressed Instructions	2.0	Frozen	36
B	Standard Extension for Bit Manipulation	0.90	Open	42
J	Standard Extension for Dynamically Translated Languages	0.0	Open	Undefined Yet
T	Standard Extension for Transactional Memory	0.0	Open	Undefined Yet
P	Standard Extension for Packed-SIMD Instructions	0.1	Open	Undefined Yet
V	Standard Extension for Vector Operations	0.7	Open	186
N	Standard Extension for User-Level Interrupts	1.1	Open	3
H	Standard Extension for Hypervisor	0.0	Open	2
S	Standard Extension for Supervisor-level Instructions	1.12	Open	7

Naming Convention

RISC-V defines an exact order that must be used to define the RISC-V ISA subset:
RV [32, 64, 128] I, M, A, F, D, G, Q, L, C, B, J, T, P, V, N

For example, RV32IMAFDQC is legal, whereas RV32IMAFDCQ is not.