LED TIMPANI Controller

C-based LED controller using TIMPANI real-time signal (SIGRTMIN+2).

Overview

This controller receives periodic signals from TIMPANI-N runtime and toggles an LED accordingly. Unlike sleep-based approaches, signal-based control maintains precise timing even under CPU load.

Architecture

┌─────────────────────────────────────────────────────────────┐
│                   LED TIMPANI Controller                    │
│                                                             │
│  ┌─────────────────┐  SIGRTMIN+2   ┌─────────────────────┐ │
│  │   Main Thread   │◄──────────────│     TIMPANI-N       │ │
│  │  (sigtimedwait) │               │  (500ms periodic)   │ │
│  └────────┬────────┘               └─────────────────────┘ │
│           │                                                 │
│           ▼                                                 │
│  ┌─────────────────┐                                        │
│  │  Arduino LED    │   Serial: /dev/arduino_led_timpani     │
│  │  (toggle ON/OFF)│   Baud: 115200                         │
│  └─────────────────┘                                        │
│                                                             │
│  ┌─────────────────┐                                        │
│  │  Worker Thread  │   Continuous busy_work (CPU load sim)  │
│  │  (busy_work)    │   Iterations: BUSY_ITERATIONS env      │
│  └─────────────────┘                                        │
│                                                             │
│  ┌─────────────────┐                                        │
│  │  Metrics Thread │   HTTP :9101/metrics (Prometheus)      │
│  │  (HTTP server)  │                                        │
│  └─────────────────┘                                        │
└─────────────────────────────────────────────────────────────┘

Build

Local Build

make clean && make

Docker Build

sudo podman build -t localhost/led-timpani-controller:latest .

Environment Variables

Variable	Default	Description
BUSY_ITERATIONS	13000000	Number of iterations for busy_work loop

Prometheus Metrics

Exposed on port 9101 at /metrics:

Metric	Type	Description
led_delay_ms	gauge	Time from signal receipt to LED toggle (ms)
led_interval_ms	gauge	Actual interval between toggles (ms)
led_state	gauge	Current LED state (0=OFF, 1=ON)
led_signal_count	counter	Total number of LED toggles

curl http://localhost:9101/metrics

Synchronization

• Creates /tmp/timpani_start file on first signal (triggers led-normal-controller start)
• Writes current LED state to /tmp/timpani_led_state (for recovery sync)

Process Name

Sets process name to led_timpani via prctl(PR_SET_NAME) for TIMPANI-N identification.

Expected Behavior

Condition	Interval	Delay
No CPU Load	~500ms	<1ms
High CPU Load	~500ms	<1ms

Key Point: TIMPANI signal delivery is independent of CPU load, so timing remains precise.