# CLAUDE.md

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

## Build & Development Commands

```bash
# Install dependencies (dev extras included)
uv sync --extra dev

# Run full test suite (mock-only, no hardware needed)
uv run pytest

# Run a single test file
uv run pytest tests/test_target.py

# Run a single test
uv run pytest tests/test_target.py::test_halt

# Run tests excluding hardware-dependent tests (explicit)
uv run pytest -m "not hardware"

# Lint
uv run ruff check src/ tests/
uv run ruff format --check src/ tests/

# Auto-fix lint/format
uv run ruff check --fix src/ tests/
uv run ruff format src/ tests/

# Run the CLI against a live OpenOCD instance
uv run openocd-python info
uv run openocd-python repl
```

## Architecture

### Dual Async/Sync API

Every subsystem exists as an async primary class and a `Sync*` wrapper. The async classes use `TclRpcConnection`; sync wrappers call `asyncio.run_until_complete()` on an internally-managed event loop.

Entry points:
- `Session.connect()` / `Session.start()` -- async context managers
- `Session.connect_sync()` / `Session.start_sync()` -- sync context managers returning `SyncSession`

### Lazy Subsystem Initialization

Session properties (`target`, `memory`, `registers`, `flash`, `jtag`, `breakpoints`, `rtt`, `svd`, `transport`, `events`) are lazily instantiated on first access. Each subsystem holds a reference to the shared connection.

### Connection Layer

`TclRpcConnection` (primary) speaks the OpenOCD TCL RPC binary protocol on port 6666: command bytes terminated by `\x1a`, response bytes terminated by `\x1a`. It uses a **dual-socket design** -- a primary socket for request/response and a separate notification socket for async target events -- to prevent command/event interleaving. An async lock serializes commands.

`TelnetConnection` is a fallback for environments without TCL RPC.

Both implement the abstract interface in `connection/base.py`.

### Type System

All return types are **frozen dataclasses** in `types.py`. Nothing mutable leaves the API surface. The exception hierarchy in `errors.py` provides fine-grained error types rooted at `OpenOCDError`.

### Parsing Strategy

OpenOCD has no structured output format. Every subsystem uses regex parsing against command output strings. When modifying parsers, test against the mock server responses in `tests/mock_server.py` -- those strings are copied from real OpenOCD output.

### SVD Integration

The `svd/` package wraps `cmsis-svd` to decode peripheral registers into named bitfields. It ties SVD metadata to live memory reads: `svd.read_register("GPIOA", "ODR")` returns a `DecodedRegister` with field names and values.

## Testing

Tests run against `MockOpenOCDServer` (`tests/mock_server.py`), a TCP server that speaks the TCL RPC protocol and returns hardcoded responses for ~30 commands. The three core fixtures in `conftest.py`:
- `mock_ocd` -- starts/stops the mock server, yields `(host, port, server)`
- `connection` -- a `TclRpcConnection` connected to the mock
- `session` -- a full `Session` connected to the mock

All async tests run automatically via `asyncio_mode = "auto"` in pyproject.toml.

The `@pytest.mark.hardware` marker gates tests that need a physical DAP-Link probe.

## Ruff Configuration

Target: Python 3.11, 100-char lines. Rule sets: E, F, I, UP, B, SIM.

## Key Constraints

- This library is used in safety-critical contexts (avionics, medical, automotive). Defensive parsing and explicit error handling matter.
- OpenOCD output varies between versions. Parsers must handle multiple formats; check existing regex patterns before assuming a single format.
- The sync API must never be called from inside an already-running async event loop (guarded in `SyncSession._get_or_create_loop()`).
- Date-based versioning: `YYYY.MM.DD` format.