ESP32-S31

Original Article ↗ Hacker News Discussion ↗

Architecture & ISA

  • Strong enthusiasm that ESP32-S31 uses RISC‑V, seen as better for open tooling than Xtensa.
  • The core supports RV32IMAC (integer, multiply/divide, atomics, compressed), with additional messy “Z*” style extensions discussed more generally for RISC‑V complexity.
  • Some lament the move away from Xtensa, which is described as elegant, but acknowledge RISC‑V’s licensing and ecosystem benefits.
  • Clarified that Espressif’s S/C/P naming refers to product category, not ISA; S31 shows Espressif is now “all‑in” on RISC‑V.

SIMD, FPU & “AI” Claims

  • S31 has SIMD on one HP core and single‑precision FPU on both HP cores. SIMD is said to be compatible with ESP32-P4 rev 3.x and evolved from S3.
  • Some disappointment that only one core has SIMD and SIMD details are still largely undocumented; people rely on esp-nn / esp-dsp sources.
  • Edge AI/ML claims are viewed skeptically: vision transformers / “Depth Anything” scale models are considered unrealistic here.
  • Consensus: small, quantized CNNs and audio tasks (wake word, simple classification like “cat on keyboard”) are plausible; memory is the main limiter.

Peripherals, Motor Control & Timing

  • Appreciated features: CAN‑FD, multiple MCPWM blocks (4), Bitscrambler peripheral (PIO‑like), FPU, crypto accelerators (SHA, AES, ECC, RSA, ECDSA).
  • Concern that ADC conversion time may be ~10 µs (based on other ESP parts), too slow for some advanced motor control strategies that need ≲1 µs and very tight control‑loop latency.
  • Extensive sub‑discussion on field‑oriented control, current sensing schemes, loop stability, and practical switching frequency limits.

Networking & Protocols

  • Big plus: integrated Wi‑Fi + BLE 5.4 (with LE Audio / LC3) plus gigabit Ethernet MAC (via external PHY). Use as router/VPN endpoint deemed theoretically possible but likely throughput‑limited.
  • Wired Ethernet uses RMII/RGMII via dedicated pins and an external PHY + magnetics.
  • Z‑Wave support deemed impossible here due to frequency and licensing; Zigbee/Thread mentioned as more natural fits on other Espressif parts.

Tooling, Ecosystem & Use Cases

  • Rust ecosystem praised: standard RISC‑V targets, official Espressif Rust HAL, active vendor participation.
  • People are excited for WROOM modules and dev boards (some already on AliExpress), using S31 as a “new default” ESP32 replacement for hobby and low‑volume products.
  • Use cases mentioned: LED art (WLED), multimedia/HDMI‑style pixel crunching, audio experiments, TLS‑enabled IoT with hardware crypto.

Concerns: Openness, Blobs & Naming

  • Wi‑Fi/BT stacks still rely on closed blobs; open MAC work exists but not complete.
  • Some worry about China‑based manufacturing and supply‑chain or security risks; others see all large vendors as similarly untrustworthy.
  • Many criticize the “ESP32-*” naming sprawl as confusing, though others note this mirrors STM32‑style family branding and signals ESP‑IDF compatibility.