Add CLAUDE.md with project guidance

Document the project overview, build commands, and architecture
for the oneUpPower kernel module and oneUpMon monitor app.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

CLAUDE.md

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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
+
+Argon ONE UP is a hardware support package for the Argon40 ONE UP laptop (Raspberry Pi-based). It consists of two main components:
+
+1. **oneUpPower** - A Linux kernel module (`battery/oneUpPower.c`) that provides battery monitoring and automatic shutdown via the Linux power supply framework. Communicates with the battery management IC over I2C (bus 1, address `0x64`).
+2. **oneUpMon** - A PyQt6 desktop monitoring application (`monitor/oneUpMon.py`) that displays real-time CPU, disk I/O, network, temperature, and fan speed charts.
+
+Only 64-bit Raspberry Pi OS is officially supported.
+
+## Build Commands
+
+### Kernel Module (battery/)
+
+```bash
+cd battery
+./firsttime          # Install build dependencies (detects OS: Debian/Alpine/Ubuntu)
+./build              # Compile oneUpPower.ko using kernel build system
+sudo ./install       # Install module, add to /etc/modules, create modprobe config
+sudo ./remove        # Unload and remove the module
+./setupdkms          # Optional: register with DKMS for auto-rebuild on kernel updates
+```
+
+The build uses the standard Linux kernel module build system (`make -C /lib/modules/$(uname -r)/build M=$(pwd) modules`).
+
+### Monitor Application
+
+```bash
+python3 monitor/oneUpMon.py
+```
+
+Python dependencies: PyQt6 (with QtCharts), gpiozero, RPi.GPIO, smartmontools (for drive temps).
+
+## Architecture
+
+### Kernel Module (battery/oneUpPower.c)
+
+- Registers two power supplies with the kernel: `BAT0` (battery) and `AC0` (AC adapter)
+- Spawns a kernel thread (`system_monitor`) polling I2C registers every ~1 second
+- Reads SOC from registers `0x04/0x05`, current direction from `0x0E/0x0F`
+- Triggers graceful shutdown via `call_usermodehelper("/sbin/shutdown")` when unplugged and SOC drops below threshold
+- Module parameter `soc_shutdown` (0-20): 0 disables auto-shutdown, 1-20 sets the SOC% threshold (default 5)
+- Configured in `/etc/modprobe.d/oneUpPower.conf`
+
+### Monitor Application (monitor/)
+
+- **oneUpMon.py**: Main PyQt6 window with a grid of rolling charts (CPU, disk I/O, network, temperatures/fan). Uses `RollingChart` (fixed Y-axis) and `RollingChartDynamic` (auto-scaling Y-axis) chart classes. 60-second rolling window.
+- **systemsupport.py**: Data collection layer. Reads `/proc/stat` for CPU load, `/sys/block/*/stat` for disk I/O, `/sys/class/net/*/statistics/` for network, and runs `smartctl` for drive temperatures.
+- **configfile.py**: INI config parser for `/etc/sysmon.ini` (drive/network filtering, smartctl options).
+- **fanspeed.py**: Reads case fan RPM via GPIO pulse counting.
+
+### Other Directories
+
+- **config/**: Raspberry Pi boot firmware config fragments (fan settings, overclock)
+- **fioscript/**: FIO benchmark job files for NVME drive testing
+- **archive/**: Legacy Argon40-supplied Python scripts (three versions: kickstarter, latest, original_beta) - reference only, not actively developed