System Operation

Status LED Indicators

HALPI2 features five RGB LEDs that provide visual feedback about system status and power conditions.

LED Status Quick Reference

Super-Capacitor Voltage Indication

During operation, the LEDs function as a voltage indicator showing super-capacitor charge level:

• LED 1: 5.0-6.0V
• LED 2: 6.0-7.0V
• LED 3: 7.0-8.0V
• LED 4: 8.0-9.0V
• LED 5: 9.0-10.0V

Power Management and Shutdown Procedures

HALPI2 features a power supply designed to withstand voltage spikes, glitches and short-term outages.

Power System Overview

HALPI2's power management system consists of:

• Wide-range power supply (11-32 VDC input with protection up to 100 VDC)
• Super-capacitor backup system for graceful shutdowns during power loss
• Current limiting (0.9A or 2.5A selectable)
• Power loss detection and automatic shutdown initiation
• Input voltage and current monitoring

The system operates in two modes: Solo Mode and Co-op Mode.

Solo Mode Operation

Solo mode provides basic autonomous operation when the HALPI daemon is not running. The controller operates independently without software communication.

Solo Mode Characteristics

• No software communication required
• Basic power loss protection - monitors input voltage and responds to power loss
• Automatic shutdown via simulated power button presses
• Limited monitoring and configuration options

Solo Mode Power Loss and Shutdown

Power Loss Detection: The controller monitors input voltage and detects power loss. A blackout timer (default 5 seconds) prevents shutdowns during brief interruptions.

Automatic Shutdown Sequence:

1. Controller detects power loss
2. Blackout timer activates to distinguish glitches from actual power loss
3. Simulated power button presses - controller sends double power-button presses to Compute Module
4. Operating system responds and begins graceful shutdown
5. Super-capacitors maintain power (typically 30-60 seconds available)
6. 60-second timeout protection - forced power-off if graceful shutdown fails
7. System remains off until power returns
8. Automatic restart when power is restored

Manual Shutdown in Solo Mode:

• Normal operating system shutdown occurs
• System automatically restarts after 5 seconds if input power remains available
• For permanent shutdown, disconnect input power after initiating graceful shutdown

When Solo Mode is Active

Solo mode occurs:

• During initial boot before HALPI daemon starts
• If HALPI daemon fails to start or is disabled
• On unsupported operating systems without the daemon
• When the daemon has crashed or become unresponsive

💡 Solo Mode Reliability

Solo mode provides essential protection but is less reliable than Co-op mode. The controller relies on simulated button presses to request shutdown, which may not work if the system is frozen.

Co-op Mode Operation

Co-op mode provides full power management functionality when the HALPI daemon is running and communicating with the controller.

Co-op Mode Features

• Direct software communication - real-time data exchange between controller and daemon
• Watchdog timer protection - 30-second timeout ensures system stability
• Configurable shutdown behavior - customizable timing and commands
• Real-time monitoring - comprehensive power parameter monitoring
• Advanced configuration options

Co-op Mode Power Loss and Shutdown

Power Loss Detection: The controller monitors input power and communicates events directly to the HALPI daemon. The configurable blackout timer (default 5 seconds) allows brief power interruptions without initiating shutdown.

Automatic Shutdown Sequence:

1. Controller detects power loss and communicates to HALPI daemon
2. Blackout timer assessment - daemon evaluates if power loss exceeds threshold
3. Shutdown command execution - daemon executes shutdown command (default: /sbin/poweroff)
4. Operating system graceful shutdown - applications close and filesystems unmount safely
5. Super-capacitor backup power provides energy throughout shutdown
6. Controller monitors completion - tracks when Compute Module powers off
7. 5V rail disabled when shutdown is complete
8. System remains off until input power returns
9. Restart management - based on configuration, system restarts automatically or remains off

Manual Shutdown in Co-op Mode:

• Standard graceful shutdown occurs when initiated through software
• System automatically restarts after 5 seconds if input power remains available
• To prevent automatic restart, disconnect power or configure auto_restart to false

Watchdog Protection

Co-op mode includes watchdog timer protection:

• 30-second communication timeout - daemon must communicate with controller regularly
• Automatic recovery - system reboots if communication stops
• Software failure protection - ensures recovery from daemon crashes or system hangs
• "Feeding the watchdog" - daemon sends regular status updates to reset timer

When Co-op Mode is Active

Co-op mode occurs when:

• HALPI daemon is running and healthy
• Communication between daemon and controller is established
• System operates on a supported operating system
• Full system monitoring and control features are available

🔧 Verifying Co-op Mode

Check daemon status: systemctl status halpid

View controller state: halpi status

For further information on the halpi command, see the Software Guide.

Backup Power and Capacitor System

Both modes rely on the super-capacitor backup system for graceful shutdown protection:

Backup Power Duration:

• Super-capacitors provide 30-60 seconds of backup power
• Duration depends on system load and connected peripherals
• Sufficient time for safe file system closure and process termination
• Not designed for continued operation during extended outages

Charging Characteristics:

• Charging time: 25 seconds with 0.9A current limit
• Charging time: 9 seconds with 2.5A current limit
• Visual charging progress shown through LED progression (red fill pattern)

⚠️ Power Loss Protection Limitation

The super-capacitor system is designed for graceful shutdown, not continued operation. Do not rely on it for extended power outages.

Manual Shutdown Considerations

HALPI2 prioritizes automated operation and recovery, affecting manual shutdown behavior.

Automatic Restart Behavior

By default, HALPI2 restarts after manual shutdowns when input power remains available:

• Manual shutdowns result in normal operating system shutdown
• 5-second grace period follows shutdown completion
• System automatically restarts to maintain operational availability
• Ensures recovery from accidental shutdowns

Intentional Shutdown Methods

For permanent shutdown, use one of these approaches:

Power Disconnection Method:

1. Initiate graceful shutdown through software
2. Wait for shutdown completion (LEDs turn off)
3. Disconnect input power to prevent automatic restart

Configuration Method:

1. Disable automatic restart: halpi config set auto_restart false
2. Initiate shutdown through software
3. System remains off after shutdown completion

Standby Mode (Future):

🔧 Feature Status

Standby mode functionality is planned for future firmware releases. This will allow the Compute Module to be powered off while the HALPI2 controller remains active, waiting for wake-up events.