Driving an Undocumented 3nm ASIC with an ESP32: Inside the First Sub-10 J/TH Open-Source Bitcoin Miner

Description and use

An ESP32‑S3 drives an undocumented 3 nm BM1373 ASIC, providing full control and telemetry via REST API, achieving 4.4 TH/s at 9.5 J/TH stock and up to 11.6 TH/s when overclocked.

Problem

A $3 microcontroller must control Bitmain’s undocumented 3nm BM1373 ASIC, which lacks datasheets, firmware, or SDKs.

Outcome

The ESP32‑S3 can fully control the BM1373 ASIC, achieving 4.4 TH/s at 9.5 J/TH in stock mode and up to 11.6 TH/s with overclocking, while providing per‑chip telemetry via a REST API.

Workflow

• Discover chips on the bus and wake them up
• Negotiate baud rate to reach operational speed
• Write registers to set frequency and core voltage
• Distribute block header work across chips
• Collect and map nonce results back to work

Evidence

The esp‑miner firmware (GPL‑3.0, maintained by the Open Source Miners United community) packages it into something an ESP32‑S3 can run: chip drivers, a stratum client, a self‑hosted web UI (AxeOS), and a REST API for telemetry.

Source

Stock is 327 MHz / 1,000 mV: 4.4 TH/s at ~42 W, the efficient point on the curve.

Source