Open standard • Modular ISA • Scalable performance

RISC-V technology and the ISA — including the Vector Extension (RVV).

RISC-V is an open instruction set architecture (ISA) that scales from tiny MCUs to Linux-capable processors. Its modular design lets hardware vendors add standardized extensions, including the RISC-V Vector Extension (RVV) for portable SIMD-style acceleration.

Explore RVV vectors Developer notes

What is RISC-V?

An open instruction set

An ISA defines the contract between software and the CPU. RISC-V is openly specified, enabling broad adoption without proprietary ISA licensing.

Open standard Multi-vendor No lock-in

Designed to scale

RISC-V spans embedded microcontrollers, application processors, and accelerators. The same fundamentals apply across the range, with extensions to match the target.

MCU → Linux Portable software Ecosystem growth

Tooling is mature

GCC/LLVM toolchains, debuggers, and operating systems support RISC-V, making it practical for teaching, research, and product development.

GCC/LLVM Linux-capable Debuggable

ISA basics: base + privileges

Base ISAs (RV32 / RV64)

The base ISA defines registers, integer arithmetic, loads/stores, branches, and calling conventions. RV32 targets 32-bit environments; RV64 supports 64-bit addressing and wider operations.

Registers Loads/stores Control flow

Privilege modes

Modern systems rely on privilege levels for isolation and OS support. Typically you’ll encounter: Machine (M) for low-level control, Supervisor (S) for OS kernels, and User (U) for applications.

M-mode S-mode U-mode
Quick decode: an ISA string like rv64imafdc means 64-bit base + a set of extensions. Many Linux-class cores are commonly summarized as rv64gc (where g is a shorthand bundle).

Modular extensions (why they matter)

Extension What it adds Typical impact
I (Base) Integer ISA (required foundation) Baseline software compatibility
M Integer multiply/divide Better performance for arithmetic-heavy code
A Atomics Lock-free primitives, OS & multithreading support
F/D Single/double-precision floating point Scientific, DSP, graphics workloads
C Compressed 16-bit instruction encodings Smaller binaries, improved I-cache efficiency
V Vector Extension (RVV) Portable vectorization across varying hardware widths
Key idea: extensions allow CPUs to target cost/power/performance needs while keeping a shared core ISA that compilers and OSes can rely on.

RISC-V Vector Extension (RVV): the big picture

Length-agnostic vectors

RVV is designed so that the same program can run efficiently on implementations with different physical vector register widths. Instead of hard-coding “128-bit” or “256-bit” vectors, code adapts to the available vector length at runtime.

Portable SIMD Scales by hardware Vector-length agnostic

Masks, types, and LMUL

RVV supports vector masks for predication and offers flexible element widths (8/16/32/64-bit, etc.). “LMUL” lets code group registers to act like wider vectors when beneficial.

Predication Variable element width Register grouping

Mental model: vector loops that adapt

A typical RVV loop chooses a vector length for the remaining elements (via vsetvl), then performs vector operations on that chunk. This avoids a scalar “tail loop” in many cases. 

while (n > 0) {
  vl = vsetvl(n);         // pick a VL supported by the hardware (<= n)
  v = load(vptr, vl);     // load vl elements
  v = f(v);               // compute (add/mul/exp/etc.)
  store(out, v, vl);      // store vl elements
  vptr += vl; out += vl;
  n -= vl;
}

Compilers can emit this pattern automatically when targeting RVV, or you can use RVV intrinsics for explicit control in performance-critical code.

Where RVV helps

Image/audio processing, cryptography, ML kernels, compression, and data-parallel loops where throughput matters.

Why it’s different

Programs are less tied to a single vector width, which can improve portability across vendors and generations.

What to watch

Ensure your toolchain flags, libraries, and runtime environment are built for the target ISA + V.

Developer notes: compiling & deploying

Toolchain targeting

For portable binaries, target the minimum ISA you need. For optimized builds, compile for the exact CPU feature set (including RVV) and validate on real hardware. 

# Illustrative intent (flags vary by toolchain/vendor):
# - target ISA: rv64 + gc + v (vectors)
# - enable vectorization (where supported)
cc -O3 -march=rv64gcv -mabi=lp64d your_code.c

The safest approach is to keep a “baseline” build for compatibility and an “optimized” build for specific boards/SoCs.

Practical checklist

  • Identify the ISA: confirm RV32/RV64 and which extensions are present (especially V).
  • Match the ABI: choose the correct ABI (e.g., lp64/lp64d for RV64).
  • Verify libraries: math/crypto/ML libs may have RVV-optimized code paths.
  • Measure: vector speedups depend on memory bandwidth, data layout, and compiler choices.
march ABI Benchmarking
Takeaway: RVV is most powerful when you write (or let the compiler generate) vector loops that naturally scale across different vector lengths, then verify with profiling on your target board.