swaits
0e9315280b
Heltec V3 (ESP32-S3) requires the espup Xtensa toolchain fork, which violates the standard-toolchain-only principle. Removed until upstream Rust supports Xtensa targets via stock rustup. Also removes all #[allow(dead_code)] band-aids — unused items are deleted rather than suppressed. DESIGN.md updated with standard toolchain principle (#10) and peripheral model (input/telemetry slots).
100 lines
4.1 KiB
Markdown
100 lines
4.1 KiB
Markdown
# Design Principles
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These are the non-negotiable first principles of this project. Every design decision,
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naming choice, module boundary, and abstraction is evaluated against them. When in
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doubt, choose simplicity and clarity over cleverness.
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## What This Is
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A transparent LoRa radio over USB. Plug the dongle into your PC, talk to any LoRa
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radio within range. That's it.
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## What This Is Not
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Not a mesh network node. Not a Meshtastic device. Not a protocol implementation. Not
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an application framework. This firmware has no opinion about what you do with your
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radio — it just gives you clean access to it.
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## Principles
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1. **Single purpose.** Transparent LoRa radio over USB. No mesh, no routing, no
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application logic. Ever.
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2. **Protocol-agnostic.** The firmware is a dumb pipe. It exposes clean LoRa
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parameters (frequency, bandwidth, spreading factor, coding rate, sync word, TX
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power) and nothing else. No raw register access, no chip-specific leakage.
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3. **Host-driven.** The firmware makes zero autonomous decisions. The radio idles on
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boot until the host commands it. No persistence across reboots. The host is always
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in control.
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4. **Zero-config.** Boots, enumerates USB, waits for commands. The host plugs in and
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goes.
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5. **Robustness over features.** Tasks never panic. Errors are reported to the host.
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The radio self-recovers. Ship fewer features, but make them bulletproof.
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6. **Minimal footprint.** Avoid heavy dependencies. Keep the binary small. Every
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dependency must justify its inclusion.
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7. **Auto-detect peripherals.** If the board has a display, keyboard, or sensors,
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use them. No user configuration required.
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8. **World-class Rust.** Fully leverage the type system for safety. Strict `no_std`.
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Always clippy-clean. Thoughtfully designed — everything has an obvious home.
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Anyone who reads this code should immediately think *"this is nice."*
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9. **Easy board support.** Adding a new board means dropping a `.rs` file and adding
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a Cargo feature. Nothing else changes.
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10. **Standard toolchain only.** No custom Rust forks, no `espup`, no special SDKs.
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If a board can't build with stock `rustup`, it doesn't ship. This rules out
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Xtensa-based ESP32 chips (S2, S3) until upstream Rust fully supports them.
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RISC-V ESP32 variants (C3, C6, H2) are fine.
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## Architecture
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```
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Host PC
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│ USB CDC-ACM (COBS-framed postcard)
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▼
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usb_task ──Command──► radio_task ──► SX1262
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◄──Response── │
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StatusWatch
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▼
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display_task (optional) ──► OLED/TFT
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```
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Each task exclusively owns its peripheral. No shared state except typed channels and
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a watch signal. Pure actor model.
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## Peripheral Model
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Boards can have optional peripherals beyond the radio and USB. The board's
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`into_parts()` returns `Option<T>` slots for each, and the corresponding task is
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only spawned when present.
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| Peripheral | Slot | Task | Examples |
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|---|---|---|---|
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| Display | `Option<DisplayParts>` | `display_task` | SSD1306 OLED, ST7789 TFT |
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| Input | `Option<InputParts>` | `input_task` | T-Deck keyboard, buttons |
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| Telemetry | `Option<TelemetryParts>` | `telemetry_task` | Battery voltage, temperature |
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**Board files are always separate.** A T-Deck is `t_deck.rs`, not a variant of
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Heltec V3. Each board owns its own init code and pin mappings. Shared logic between
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boards that use the same MCU can be factored into helper modules if it earns its
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keep, but never prematurely.
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## Technical Decisions
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| Decision | Choice | Why |
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|---|---|---|
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| USB framing | COBS + postcard | Compact, `no_std` native, battle-tested |
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| Serialization | postcard + serde | Zero-alloc binary codec, perfect for embedded |
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| Async runtime | Embassy | De facto standard for async embedded Rust |
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| Display | Radio status dashboard | Freq, BW, SF, packet counts, RSSI/SNR |
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| Boot behavior | Idle until host commands | Host-driven principle |
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| Persistence | None | Always start fresh, true dumb pipe |
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| Board codegen | Jinja2 via build.rs | Auto-discovers boards from filesystem |
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| Rust toolchain | Standard `rustup` only | No forks, no espup, no special SDKs |
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