sen5x 0.2.0

Rust driver for the Sensirion SEN5x series. All-in-one sensor solution platform for the accurate measurement of various environmental parameters, such as particulate matter, volatile organic compounds (VOCs), oxidizing gases, such as nitrogen oxide compounds (NOx), as well as humidity & temperature
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# CLAUDE.md

This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.

## Project Overview

`no_std` Rust driver for the Sensirion SEN5x environmental sensor series (PM, VOC, NOx, humidity, temperature). Communicates over I2C using `embedded-hal` 1.0 blocking traits with optional `embedded-hal-async` support. Based on the Sensirion C reference implementation and follows the same patterns as the scd4x-rs driver.

## Build & Test Commands

```bash
cargo build                                # Build the library
cargo test                                 # Run tests (uses embedded-hal-mock)
cargo clippy                               # Lint
cargo doc --open                           # Generate and view docs
cargo build --features embedded-hal-async  # Build with async support
cargo build --features defmt               # Build with defmt support
```

## Architecture

- **`sen5x/mod.rs`** — Main driver struct `Sen5x<I2C, D>` generic over I2C bus and delay. Tracks `is_running` state to enforce command validity (idle-only vs allowed-during-measurement). All sensor operations go through internal helpers: `write_command`, `write_command_with_data` (single u16), `write_command_with_words` (multi-word), and `delayed_read_cmd`. I2C address is fixed at `0x69`.
- **`sen5x/async_impl.rs`** — `Sen5xAsync<I2C, D>` mirroring all public methods as `async fn`. Uses `sensirion_i2c::i2c_async`.
- **`commands.rs`** — `Command` enum (28 variants) mapping to `(u16_command_code, u32_delay_ms, bool_allowed_if_running)` tuples.
- **`types.rs`** — Data structs: `SensorData` (f32 scaled), `RawSensorData` (integer ticks), `RawMeasurementValues`, `PmValues` (extended PM), `TemperatureOffsetParameters`, `AlgorithmTuningParameters`, `VersionInfo`.
- **`error.rs`** — Error type wrapping I2C errors and CRC failures, with optional `defmt` and `thiserror` support.

## Key Conventions

- The library is `#![no_std]` (std only enabled in test cfg or via `std` feature).
- I2C response buffers use Sensirion's format: 2 data bytes + 1 CRC byte per word. Buffer indices skip every 3rd byte for CRC.
- Multi-word write commands (temperature offset, algorithm tuning, VOC state, fan interval) use `write_command_with_words` with a stack-allocated `[u8; 20]` buffer.
- Serial number and product name are ASCII strings returned as `[u8; 32]`.
- Tests use `embedded-hal-mock::eh1` with `NoopDelay`, `word()` helper for CRC, and `destroy()` + `done()` pattern.
- Features: `embedded-hal-async`, `defmt`, `thiserror`, `std`.