strix/README.md

# STRIX
### Satellite True Random Information eXtractor

[![Arduino MKR Vidor 4000](https://img.shields.io/badge/Arduino-MKR%20Vidor%204000-00878F?logo=arduino&logoColor=white)](https://docs.arduino.cc/hardware/mkr-vidor-4000/)
[![Built with Devbox](https://www.jetify.com/img/devbox/shield_galaxy.svg)](https://github.com/jetify-com/devbox/)
[![License: Apache 2.0](https://img.shields.io/badge/License-Apache_2.0-blue)](LICENSE)
[![AI-DECLARATION: copilot](https://img.shields.io/badge/䷼%20AI--DECLARATION-copilot-fee2e2?labelColor=fee2e2)](https://ai-declaration.md)

A portable wireless True Random Number Generator built on an Arduino MKR Vidor 4000.

## Design

Entropy comes from FPGA ring oscillators whose sampled timing jitter is XOR-combined into output bits, with no pseudo-random post-processing. A SAMD21 serves the results over USB, over HTTP on its own WiFi access point (stationary mode, on a charger), or over Bluetooth LE (mobile mode, on battery).

- 4 independent generators × 90 ring oscillators. Each generator XORs its rings every 120 MHz clock (spatial) and then several consecutive bits (temporal, default 5): about 24 Mbps per generator.
- Separate stream per generator, plus a combined stream of all healthy generators
- On-device health tests per generator: NIST SP 800-90B repetition count and adaptive proportion, plus a dead-ring monitor
- Live statistics per trial: bias, z-score, random walk and lag-1 autocorrelation, with rolling and cumulative windows
- Configurable random-walk / majority-vote bias amplifier on a bias path and an autocorrelation path, with sub-trial voting
- Von Neumann extractor that can be toggled on the stream, statistics and amplifier paths
- Per-second trials in Global Consciousness Project format (200-bit XOR-masked sums per generator, plus full-rate sums), with Stouffer Z and network variance
- Raw ring captures and frequency measurement for characterization

```mermaid
flowchart LR
    subgraph FPGA["FPGA: Cyclone 10 LP, 120 MHz from a PLL on the SAMD21's 48 MHz clock"]
        direction LR
        subgraph GEN["4 generators"]
            direction TB
            RO["90 ring oscillators<br/>3 taps XORed per ring"] --> SMP["2-flip-flop sampling"]
            SMP --> SX["spatial XOR<br/>of all rings"]
            SX --> TX["temporal XOR<br/>of 1-8 bits"]
        end
        SMP --> HM["health monitors<br/>repetition count, adaptive<br/>proportion, dead rings"]
        SX --> HM
        TX --> SEL["healthy generators<br/>g0-g3 and combined XOR"]
        HM -->|healthy| SEL
        SEL --> ST["entropy stream<br/>4 KB FIFO"]
        SEL --> STATS["statistics<br/>per-trial counts"]
        SEL --> AMP["bias amplifier<br/>2 paths, 3 stages"]
        SEL --> GCP["GCP trials<br/>per second"]
        GEN -.-> CAP["raw capture,<br/>frequency counter"]
        ST & STATS & AMP & GCP & CAP & HM --> REG["SPI registers"]
        PT["WiFi module<br/>pin pass-through"]
    end
    REG <-->|SPI 8 MHz| MCU["SAMD21 firmware"]
    MCU <--> PT
    PT <--> NINA["NINA-W102<br/>WiFi and BLE"]
    MCU --> USB["USB serial"]
    NINA --> HTTP["HTTP on its own<br/>access point"]
    NINA --> BLE["BLE GATT service"]
```

The USB, HTTP and BLE API is documented in [arduino/strix/API.md](arduino/strix/API.md).

## Command-line client

`tools/strix.py` talks to the device over USB; run it with `devbox run strix <command>` or `uv run tools/strix.py <command>`. It finds the board by its USB ID (override with `--port` or `STRIX_PORT`).

| Command | Does |
|---|---|
| `id`, `health`, `amp`, `get` | Prints the device's reply |
| `stats [--reset]` | Prints the statistics, or restarts them |
| `set KEY VALUE` | Changes a setting (keys in the API documentation) |
| `entropy N [--out FILE]` | N entropy bytes as hex, or binary into a file |
| `watch stats\|amp` | Prints every new trial until Ctrl-C |
| `gcp [--log FILE] [--full] [--seconds N]` | Follows the per-second GCP-format trials |
| `send LINE` | Sends any command line and prints the reply |

`gcp` prints one line per second: UTC time, second number, the four 200-bit sums, Stouffer Z, Z², and the cumulative Z² − 1 with its p = 0.05 envelope (`*` when outside). `--full` tracks the full-rate trials instead. It reconnects after USB dropouts and fills missed seconds from the device's 60-second history. `--log` appends GCP-style CSV rows, `13,<unix time>,<UTC date-time>,<g0>,<g1>,<g2>,<g3>` (empty for unhealthy generators), after a `12,gmtime,Date/Time,g0,g1,g2,g3` header.

## HTTP server for a USB-connected STRIX

`tools/strix_serve.py` (`devbox run serve`) serves the device's WiFi HTTP API routes for a board on USB, so the same clients work with either. Options: `--listen ADDRESS:PORT` (default `127.0.0.1:8080`, use `0.0.0.0:8080` for the network), `--port` for the serial port, `--gcp-log FILE` to append every per-second trial to a JSON-lines file, and `--set-token-file FILE` to require that file's token for `/set` (header `Authorization: Bearer <token>`), for servers reachable by others.

Since only one program can use the USB port, the server follows the GCP trials itself: `/gcp` serves the last hour instead of the device's 60 seconds, and every record gets a `time` field (Unix time at the start of the second, from the host clock). `/entropy` accepts up to 1 MiB. The server reconnects after USB dropouts; requests in the meantime get status 503.

The API is described in OpenAPI 3 at `/openapi.json` (`tools/strix_openapi.json`), with an interactive Swagger UI at `/docs` (its scripts load from a CDN).

## TODO

- WiFi credentials stored on the device instead of compile-time defaults
- Battery pack
- 3D case

---

## [Development Notes](NOTES.md)