LEDMatrix/docs/ADVANCED_FEATURES.md

Advanced Features Guide

This guide covers advanced LEDMatrix features for users and developers, including Vegas scroll mode, on-demand display, cache management, background services, and permission management.

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1. Vegas Scroll Mode

Overview

Vegas scroll mode displays content from multiple plugins in a continuous horizontal scroll, similar to news tickers seen in Las Vegas casinos. Plugins contribute content segments that flow across the display in a seamless ticker-style presentation.

How a Plugin Takes Part

Each plugin has a Vegas participation:

scroll (the default):

• The plugin's content scrolls by with everyone else's
• Best for news-ticker style content: scores, headlines, prices, the time

pause:

• The scroll stops when the plugin's turn comes round
• The plugin draws the whole panel for its display duration, then the scroll resumes
• Best for content that needs to be read in full, or alerts

exclude:

• The plugin is left out of Vegas mode

A plugin declares its default; set vegas_participation in a plugin's config to override it (see Per-Plugin Configuration). Older documentation also describes a fixed segment mode; Vegas never implemented one, and it has always behaved exactly like scroll.

Configuration

Enable Vegas mode in config/config.json:

{
  "display": {
    "vegas_scroll": {
      "enabled": true,
      "scroll_speed": 50,
      "separator_width": 32,
      "plugin_order": ["clock", "weather", "sports"],
      "excluded_plugins": ["debug_plugin"],
      "target_fps": 125,
      "buffer_ahead": 2
    }
  }
}

Vegas mode can also be configured entirely from the web UI — the Display tab has a Vegas Scroll Mode section (enable toggle, scroll speed, separator width, dynamic duration, and more), so hand-editing JSON is optional.

Configuration Options:

Setting	Default	Description
enabled	false	Enable Vegas scroll mode
scroll_speed	50	Pixels per second scroll speed
separator_width	32	Width between plugin segments (pixels)
plugin_order	[]	Plugin display order (empty = auto)
excluded_plugins	[]	Plugins to exclude from Vegas mode
target_fps	125	Target frame rate
buffer_ahead	2	Number of plugins buffered ahead

This table is a subset — display.vegas_scroll supports 30 keys in total. See the full list in CONFIG_REFERENCE.md.

Live Content in the Ticker

By default (since 3.8.0) live content stays in the ticker and takes extra turns inside it, and a scoreboard that supports live cards updates the score on a card already crossing the screen (live_refresh, "Update live content while it scrolls").

To get the old behaviour back -- live content preempts Vegas mode: while any plugin reports live priority the ticker stops and that plugin's full-screen display is shown instead -- untick Keep live games in the ticker under Vegas mode, or set live_in_ticker to false:

"vegas_scroll": {
  "live_in_ticker": false
}

Until 3.8.0 false was the default and every config held it, copied from the template. The first start on 3.8.0 turns it on once (a backup of the config is kept as config.json.backup, and live_in_ticker_migrated records that it ran); a false set after that is left alone.

The weights below apply while live content is in the ticker:

"vegas_scroll": {
  "live_weight": 3,
  "favorite_live_weight": 5
}

Why weights exist

The rotation is otherwise a strict round robin — every plugin appears exactly once per cycle. With a dozen plugins enabled, a live score comes round once a lap and can be minutes old by the time you see it. A weight of N gives a plugin N slots per cycle.

The slots are placed by Smooth Weighted Round-Robin, the same scheduler the sports plugins use internally to rotate their own games. The important property is that repeats are spread through the cycle rather than clumped: three appearances in a row followed by a long silence would be worse than not boosting at all.

Twelve plugins, with a favorite's baseball game and an ordinary live hockey game (live_weight: 3, favorite_live_weight: 5):

baseball > hockey > weather  > clock  > baseball
stocks   > news   > flights  > baseball > hockey
calendar > f1     > music    > baseball > tides
birds    > hockey > baseball

18 slots for 12 plugins. Baseball appears 5 times, hockey 3, everything else once, and no plugin ever appears twice in a row — including across the seam where the cycle loops back on itself. Smooth Weighted Round-Robin schedules the heaviest item first and usually last as well, so the strip would otherwise show it twice running at exactly the one join a within-cycle check cannot see. The trailing repeat is moved into the widest remaining gap. Where a double is unavoidable — a plugin holding most of the slots has to neighbour itself — the schedule is left as it is.

Where the weight comes from

For each plugin in the rotation, in order:

1. The plugin's own answer. If it implements get_vegas_priority_weight() and returns a number, that wins. This is the only route for favorite-team awareness — the core can see that a game is live, but not whose, so a scoreboard has to say so itself.
2. The core's default. When the plugin returns None (the base-class default), a plugin where both has_live_priority() and has_live_content() are true gets live_weight.
3. Everything else gets 1.

Because of step 2, existing plugins need no changes — any scoreboard with live_priority enabled already gets extra turns. Step 1 is opt-in, for plugins that want to distinguish a favorite's game from any other live game.

Weights are clamped to 1–10. A weight of 1 is no boost; a weight below 1 would drop the plugin from the rotation entirely, which is never what is meant.

Things worth knowing

• Weights are per plugin, not per game. A scoreboard showing four live games still occupies one slot at a time, rotating its own games within that slot using its own favorite_live_boost. This controls how often the plugin comes round.
• The ticker is zero-sum. Giving baseball 5 slots does not make the cycle faster; it makes the cycle longer and everything else proportionally rarer. If you want live scores sooner in wall-clock terms, pair this with a smaller plugins_per_cycle.
• Frequency is not freshness. Each appearance redraws from the plugin's current data (refresh_updated_plugins() drops cached content when a plugin's data changes), but how current that data is depends on the plugin's own live_update_interval. Showing a stale score five times a lap is no better than showing it once.
• Everything still appears. A boost never starves another plugin out of the cycle; low-weight plugins keep their single slot.

Per-Plugin Configuration

Override Vegas behavior for specific plugins:

{
  "my_plugin": {
    "enabled": true,
    "vegas_participation": "pause",
    "display_duration": 10
  }
}

Per-Plugin Options:

Setting	Values	Description
vegas_participation	scroll, pause, exclude	How this plugin takes part: its content scrolls by, the scroll pauses for its turn and shows it full screen, or it is left out. Unset uses the plugin's own default
display_duration	seconds	How long a pause plugin holds the screen
vegas_width_pct	10–100	Width of this plugin's card, as a percentage of the panel
vegas_overflow	rotate, truncate	What to do when its content is wider than its allowance
vegas_max_width_screens	number of screens	The widest its card may be

These are core-owned settings (see PLUGIN_CONFIG_CORE_PROPERTIES.md): every plugin accepts them whether or not its own schema lists them. Set them in the plugin's section of config.json, in the web UI's Config Editor tab.

Some plugins also offer a vegas_mode setting of their own (scroll, fixed or static). It still works — static pauses, the other two scroll — but vegas_participation takes precedence, and fixed has never done anything different from scroll. The old vegas_panel_count setting never had an effect and is deprecated (removed in 3.9.0).

Plugin Integration (Developer Guide)

All of these have defaults in BasePlugin; override only what you need. The reference is PLUGIN_API_REFERENCE.md.

1. Implement Content Method:

def get_vegas_content(self):
    # Return a PIL Image, a list of Images, or None.
    # A single image is one block; a list becomes one item per image.
    return [self._render_game(game) for game in self.games]

If it returns None (the default), Vegas falls back to the plugin's scroll_helper image, then to capturing display() output (PluginAdapter.get_content() in src/vegas_mode/plugin_adapter.py).

2. Declare how the plugin takes part:

Most plugins need nothing: the default is scroll. A plugin that should pause the scroll, or stay out of Vegas, says so in manifest.json:

{
  "vegas_participation": "pause"
}

The user's own vegas_participation setting overrides the manifest. When the answer depends on state, override the method instead:

def get_vegas_participation(self):
    # 'scroll' | 'pause' | 'exclude'
    return 'pause' if self._alert_is_live() else 'scroll'

A plugin written for an older core that declares nothing keeps its behaviour: get_vegas_display_mode() returning VegasDisplayMode.STATIC pauses, get_vegas_content_type() returning 'none' excludes, and everything else scrolls. get_supported_vegas_modes(), get_vegas_segment_width() and the SCROLL / FIXED_SEGMENT distinction are deprecated (removed in 3.9.0): Vegas never read them.

Content Rendering Guidelines

Image Dimensions:

• Height: Must match display height (typically 32 pixels)
• Width: Any width for scroll (recommended 64-512 pixels); get_vegas_render_width() is the width Vegas would like, and it narrows display_manager to match while it asks. A pause plugin draws the whole panel in display().

Color Mode:

• Use RGB color mode
• 24-bit color (8 bits per channel)

Performance Tips:

1. Cache rendered images - Render in update(), not in get_vegas_content()
2. Keep images small - Larger images use more memory
3. Pre-render on update - Don't create images on-demand
4. Reuse images - Return same image if content unchanged

Example Integration

Complete example for a weather plugin:

class WeatherPlugin(BasePlugin):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        self.vegas_image = None

    def update(self):
        """Update data and pre-render Vegas image"""
        # Fetch weather data
        weather_data = self.fetch_weather()

        # Pre-render Vegas image
        self.vegas_image = self._render_vegas_content(weather_data)

    def _render_vegas_content(self, data):
        """Render weather content for Vegas mode"""
        img = Image.new('RGB', (384, 32))
        draw = ImageDraw.Draw(img)

        # Draw temperature
        draw.text((10, 0), f"{data['temp']}°F", fill=(255, 255, 255))

        # Draw condition
        draw.text((100, 0), data['condition'], fill=(200, 200, 200))

        # Draw icon
        icon = Image.open(f"assets/{data['icon']}.png")
        img.paste(icon, (250, 0))

        return img

    def get_vegas_content(self):
        """Return cached Vegas image"""
        return self.vegas_image

It scrolls, the default participation, so it declares nothing else.

System Architecture

Vegas mode consists of four core components working together to provide smooth 125 FPS continuous scrolling:

Component Overview

┌─────────────────────────────────────────────────────────────┐
│                   VegasModeCoordinator                      │
│  Main orchestrator - manages lifecycle and coordination     │
└───────┬──────────────────┬──────────────────┬──────────────┘
        │                  │                  │
        ▼                  ▼                  ▼
┌───────────────┐  ┌──────────────┐  ┌─────────────────┐
│ PluginAdapter │  │StreamManager │  │ RenderPipeline  │
│               │  │              │  │                 │
│ Converts      │─▶│ Manages      │─▶│ 125 FPS render  │
│ plugin content│  │ content      │  │ Double-buffered │
│ to images     │  │ stream with  │  │ Smooth scroll   │
│               │  │ 1-2 ahead    │  │                 │
└───────────────┘  │ buffering    │  └─────────────────┘
                   └──────────────┘

1. VegasModeCoordinator

Responsibilities:

• Initialize and coordinate all Vegas mode components
• Manage the high-FPS render loop (target: 125 FPS)
• Handle live priority interruptions
• Process config updates during runtime
• Provide status and control interface

Key Features:

• Thread-safe state management
• Config hot-reload support
• Live priority integration
• Interrupt checking for yielding control back to display controller
• Static pause handling (pauses scroll when content fully visible)

Main Loop:

1. Check for interrupts (live priority, on-demand, config updates)
2. If static pause active, wait for duration
3. Otherwise, delegate to render pipeline for frame rendering
4. Sleep to maintain target FPS

2. StreamManager

Responsibilities:

• Manage plugin content streaming with look-ahead buffering
• Coordinate with PluginAdapter to fetch plugin content
• Handle plugin ordering and exclusions
• Optimize content generation timing

Buffering Strategy:

• Buffer Ahead: 1-2 panels (configurable)
• Just-in-Time Generation: Fetch content only when needed
• Memory Efficient: Only keep necessary content in memory

Content Flow:

1. Determine which plugins should appear in stream
2. Respect plugin_order configuration (or use default order)
3. Exclude plugins in excluded_plugins list
4. Request content from each plugin via PluginAdapter
5. Compose into continuous stream with separators

Key Methods:

• get_next_segment() - Returns the next buffered ContentSegment (or None)
• take_next_group(count=None, offscreen_only=False) - Hands over the next slice of the rotation as (plugin_id, images) groups
• get_grouped_content_for_composition() - Buffered images grouped by plugin
• mark_plugin_updated(plugin_id) / process_updates() - Refresh one plugin's segment in place when its data changes
• refresh() - Re-read the plugin list and config
• advance_cycle() - Clear the active buffer when a scroll cycle completes

(src/vegas_mode/stream_manager.py)

3. PluginAdapter

Responsibilities:

• Convert plugin content to scrollable images
• Fetch the content of scroll plugins (a pause plugin is drawn by its own display() when the scroll pauses; see StreamManager)
• Manage fallback for plugins without Vegas support
• Cache plugin content for performance

Plugin Integration:

1. Check for Vegas support:

   • Calls get_vegas_content() if available
   • Falls back to display() method if not

2. Participation is decided by the StreamManager, not here (resolve_vegas_participation() in base_plugin.py): exclude plugins never reach the adapter, and pause plugins are not fetched.

Fallback Behavior:

• If plugin doesn't implement Vegas methods:
  • Calls plugin's display() method
  • Captures rendered display as static image
  • Scrolls it by as one block
• Ensures all plugins work in Vegas mode without explicit support

4. RenderPipeline

Responsibilities:

• High-performance 125 FPS rendering
• Double-buffered composition for smooth scrolling
• Scroll position management
• Frame rate control

Rendering Process:

1. Fetch Stream Content: Get current stream from StreamManager
2. Extract Viewport: Calculate which portion of stream is visible
3. Compose Frame: Create frame with visible content
4. Double Buffer: Render to off-screen buffer
5. Display: Swap buffer to display
6. Advance: Update scroll position based on speed and elapsed time

Performance Optimizations:

• Double Buffering: Eliminates flicker
• Viewport Extraction: Only processes visible region
• Frame Rate Control: Precise timing to maintain 125 FPS
• Pre-rendered Content: Plugins pre-render during update()

Scroll Speed Calculation: motion is by elapsed time; target_fps paces the render loop, not the speed.

# frame_based_scrolling: false
scroll_position += scroll_speed * elapsed_time            # scroll_speed in px/s
# frame_based_scrolling: true (the default) -- not stepping, just a clamp
applied = clamp(scroll_speed * scroll_delay, 0.1, 5) / scroll_delay
scroll_position += applied * elapsed_time

Component Interactions

Initialization Flow:

1. VegasModeCoordinator created
2. Coordinator creates PluginAdapter
3. Coordinator creates StreamManager (with PluginAdapter)
4. Coordinator creates RenderPipeline (with StreamManager)
5. All components initialized and ready

Render Loop Flow:

1. Coordinator starts render loop
2. Check for interrupts (live priority, on-demand)
3. RenderPipeline.render_frame():
   a. Request current stream from StreamManager
   b. StreamManager uses PluginAdapter to get plugin content
   c. PluginAdapter calls plugin Vegas methods or fallback
   d. Stream content returned to RenderPipeline
   e. RenderPipeline extracts viewport and renders
4. Update scroll position
5. Sleep to maintain target FPS
6. Repeat from step 2

Config Update Flow:

1. Config change detected by Coordinator
2. Set _pending_config_update flag
3. On next render loop iteration:
   a. Pause rendering
   b. Update VegasModeConfig
   c. Notify StreamManager of config change
   d. StreamManager refreshes stream
   e. Resume rendering

Thread Safety

All components use thread-safe patterns:

• Coordinator: Uses threading.Lock for state management
• StreamManager: Thread-safe content access
• RenderPipeline: Atomic frame composition
• PluginAdapter: Stateless operations (except caching)

Performance Characteristics

Frame Rate:

• Target: 125 FPS
• Actual: 100-125 FPS (depends on content complexity)
• Render time budget: ~8ms per frame

Memory Usage:

• Stream buffer: ~2-3 panels ahead
• Plugin content: Cached in plugin's update() method
• Double buffer: 2x display size

CPU Usage:

• Light load: 5-10% (simple content)
• Heavy load: 15-25% (complex content, many plugins)
• Optimized with numpy for pixel operations

Fallback Behavior

If a plugin doesn't implement Vegas methods:

• System calls the plugin's display() method
• Captures the rendered display as a static image
• Scrolls it by as one block

This ensures all plugins work in Vegas mode, even without explicit support.

---

2. On-Demand Display

Overview

On-demand display allows users to manually trigger specific plugins to show immediately on the LED matrix, overriding the normal rotation. This is useful for:

• Quick checks (weather, scores, time)
• Pinning important information
• Testing plugins during development
• Showing specific content to visitors

Priority Hierarchy

On-demand display has the highest priority:

Priority Order (highest to lowest):
1. On-Demand Display (manual trigger)
2. Live Priority (games in progress)
3. Normal Rotation

When on-demand expires or is cleared, the display returns to the next highest priority (live priority or normal rotation).

Web Interface Controls

Each installed plugin has its own tab in the second nav row of the web UI. Inside the plugin's tab, scroll to On-Demand Controls:

• Run On-Demand — triggers the plugin immediately, even if it's disabled in the rotation
• Stop On-Demand — clears on-demand and returns to the normal rotation

The display service must be running. The status banner at the top of the plugin tab shows the active on-demand plugin, mode, and remaining time when something is active.

REST API Reference

The API is mounted at /api/v3 (the api_v3 blueprint, registered in web_interface/app.py). Full details: REST_API_REFERENCE.md.

Start On-Demand Display

POST /api/v3/display/on-demand/start

# Body:
{
  "plugin_id": "weather",
  "duration": 30,        # Optional: seconds (0 = indefinite, null = default)
  "pinned": false        # Optional: keep until manually cleared
}

# Examples:
# 30-second preview
curl -X POST http://localhost:5000/api/v3/display/on-demand/start \
  -H "Content-Type: application/json" \
  -d '{"plugin_id": "weather", "duration": 30}'

# Pin indefinitely
curl -X POST http://localhost:5000/api/v3/display/on-demand/start \
  -H "Content-Type: application/json" \
  -d '{"plugin_id": "hockey-scoreboard", "pinned": true}'

Stop On-Demand Display

POST /api/v3/display/on-demand/stop

# Body:
{
  "stop_service": false  # Optional: also stop display service
}

# Examples:
# Clear on-demand
curl -X POST http://localhost:5000/api/v3/display/on-demand/stop

# Stop service too
curl -X POST http://localhost:5000/api/v3/display/on-demand/stop \
  -H "Content-Type: application/json" \
  -d '{"stop_service": true}'

Get On-Demand Status

GET /api/v3/display/on-demand/status

# Example:
curl http://localhost:5000/api/v3/display/on-demand/status

# Response:
{
  "status": "success",
  "data": {
    "state": {
      "active": true,
      "plugin_id": "weather",
      "mode": "weather",
      "duration": 30,
      "pinned": false,
      "status": "running",
      "last_updated": 1234567890.1
    },
    "service": {"active": true, "returncode": 0, "stdout": "active", "stderr": ""}
  }
}

When nothing is running on demand, data.state is {"active": false, "status": "idle", "last_updated": null}.

There is no public Python on-demand API. The display controller's on-demand machinery is internal — drive it through the REST endpoints above (or the web UI buttons). The API handlers (start_on_demand_display() / stop_on_demand_display() in web_interface/blueprints/api_v3/display.py) write a request into the cache manager under the display_on_demand_request key, which DisplayController._poll_on_demand_requests() (src/display_controller.py) picks up. A separate display_on_demand_config key is used by the controller itself during activation (_activate_on_demand()) to track what's currently running, and is cleared by _clear_on_demand().

Duration Modes

Duration	Pinned	Behavior
None	false	Use plugin's default duration, auto-clear when expires
0	false	Indefinite, clears manually or on error
> 0	false	Timed display, auto-clear after N seconds
Any	true	Pin until manually cleared (ignores duration)

Use Case Examples

Quick check (30-second preview):

curl -X POST http://localhost:5000/api/v3/display/on-demand/start \
  -H "Content-Type: application/json" \
  -d '{"plugin_id": "ledmatrix-weather", "duration": 30}'

Pin important information:

curl -X POST http://localhost:5000/api/v3/display/on-demand/start \
  -H "Content-Type: application/json" \
  -d '{"plugin_id": "hockey-scoreboard", "pinned": true}'
# ... later ...
curl -X POST http://localhost:5000/api/v3/display/on-demand/stop

Indefinite display:

curl -X POST http://localhost:5000/api/v3/display/on-demand/start \
  -H "Content-Type: application/json" \
  -d '{"plugin_id": "text-display", "duration": 0}'

Testing a plugin during development: the same call works, or just click Run On-Demand in the plugin's tab.

Best Practices

For Users:

1. Use timed display as default (prevents forgetting to clear)
2. Pin only when necessary
3. Clear when done to return to normal rotation

For Developers:

1. Validate plugin ID exists before calling
2. Provide visual feedback in UI (loading state, status updates)
3. Handle concurrent requests gracefully
4. Log on-demand activations for debugging

Security Considerations

Authentication:

• Add authentication to API endpoints
• Restrict on-demand to authorized users

Rate Limiting:

• Prevent abuse from rapid requests
• Implement cooldown between activations

Input Validation:

• Sanitize plugin IDs
• Validate duration values
• Check plugin exists before activation

---

3. On-Demand Cache Management

Overview

On-demand display uses cache keys (managed by src/cache_manager.py — file-based, not Redis) to coordinate state between the web interface and the display controller across service restarts. Understanding these keys helps troubleshoot stuck states.

Cache Keys

1. display_on_demand_request (TTL: 1 hour)

{
  "request_id": "uuid-string",
  "action": "start|stop",
  "plugin_id": "plugin-name",
  "mode": "mode-name",
  "duration": 30.0,
  "pinned": true,
  "timestamp": 1234567890.123
}

Purpose: Communication from web interface to display controller When Set: API endpoint receives request Auto-Cleared: After processing or 1 hour TTL

2. display_on_demand_config (No TTL)

{
  "mode": "mode-name",
  "duration": 30.0,
  "pinned": true
}

Purpose: Persistent configuration for display controller When Set: Controller processes start request Auto-Cleared: When on-demand stops

3. display_on_demand_state (Continuously updated)

{
  "active": true,
  "mode": "mode-name",
  "remaining": 25.5,
  "pinned": true,
  "status": "active|idle|restarting|error"
}

Purpose: Real-time state for web interface status card When Set: Every display loop iteration Auto-Cleared: Never (continuously updated)

4. display_on_demand_processed_id (TTL: 1 hour)

"uuid-string-of-last-processed-request"

Purpose: Prevents duplicate request processing When Set: After processing request Auto-Cleared: After 1 hour TTL

When Manual Clearing is Needed

Scenario 1: Stuck in On-Demand State

• Symptom: Display stays on one plugin, won't return to rotation
• Clear: config, state, request

Scenario 2: Mode Switching Issues

• Symptom: Can't change to different plugin
• Clear: request, processed_id, state

Scenario 3: On-Demand Not Activating

• Symptom: Button click does nothing
• Clear: processed_id, request

Scenario 4: After Service Crash

• Symptom: Strange behavior after crash/restart
• Clear: All four keys

Manual Recovery Procedures

Via Web Interface (Recommended):

1. Open the Cache tab in the web UI
2. Find the display_on_demand_* entries
3. Delete them
4. Restart display: sudo systemctl restart ledmatrix

Via Command Line:

The cache is stored as JSON files under one of:

• /var/cache/ledmatrix/ (preferred when the service has permission)
• ~/.ledmatrix_cache/
• /opt/ledmatrix/cache/
• $TMPDIR/ledmatrix_cache/ (fallback)

# Find the cache dir actually in use
journalctl -u ledmatrix | grep -i "cache directory" | tail -1

# Clear all on-demand keys (replace path with the one above)
rm /var/cache/ledmatrix/display_on_demand_*

# Restart service
sudo systemctl restart ledmatrix

Via Python:

from src.cache_manager import CacheManager

cache = CacheManager()
cache.clear_cache('display_on_demand_config')
cache.clear_cache('display_on_demand_state')
cache.clear_cache('display_on_demand_request')
cache.clear_cache('display_on_demand_processed_id')

CacheManager also has a delete(key) method — a thin wrapper over clear_cache(key) — so cache.delete('display_on_demand_config') works equally well.

Cache Impact on Running Service

IMPORTANT: Clearing cache keys does NOT immediately affect the running controller in memory.

To fully reset:

1. Stop the service: sudo systemctl stop ledmatrix
2. Clear cache keys (web UI Cache tab or rm from the cache directory)
3. Clear systemd environment: sudo systemctl daemon-reload
4. Start the service: sudo systemctl start ledmatrix

Automatic Cleanup

The display controller automatically handles cleanup:

• Config key: Cleared when on-demand stops
• State key: Updated every display loop iteration
• Request key: Expires after 1 hour TTL (or after processing)
• Processed ID: Expires after 1 hour TTL

---

4. Background Data Service

Overview

The Background Data Service enables non-blocking data fetching through background threading. This prevents the main display loop from freezing during slow API requests, maintaining smooth display rotation.

Benefits

Performance:

• Display loop never freezes during API calls
• Immediate response with cached/partial data
• Complete data loads in background

User Experience:

• No "frozen" display during data updates
• Smooth transitions between plugins
• Faster perceived load times

Architecture:

Cache Check → Background Fetch → Partial Data → Completion → Cache
    (0.1s)         (async)            (<1s)         (10-30s)    (cache)

Configuration

Core does not read a background_service config block: the service itself (src/background_data_service.py) is a process-wide singleton, and its worker count is whatever the first caller of get_background_service() passes. The sports scoreboard plugins read their own background_service settings and pass them to it, so the exact keys and where they sit (top level or per league) are defined by each plugin's config_schema.json. A typical block looks like:

{
  "football-scoreboard": {
    "enabled": true,
    "background_service": {
      "enabled": true,
      "max_workers": 3,
      "request_timeout": 30,
      "max_retries": 3,
      "priority": 2
    }
  }
}

Configuration Options:

Setting	Default	Description
enabled	plugin-defined	Use the background service for this plugin's fetches
max_workers	3	Max concurrent background tasks
request_timeout	30	Timeout per API request (seconds)
max_retries	3	Retry attempts on failure
priority	1	Stored on each request (higher number = higher priority, per FetchRequest), but the service runs requests in submission order; it does not reorder by priority

Performance Impact

First Request (Cache Empty):

• Returns partial data: < 1 second
• Background completes: 10-30 seconds
• Subsequent requests use cache: < 0.1 seconds

Subsequent Requests (Cache Hit):

• Returns immediately: < 0.1 seconds
• Background refresh (if stale): async, no blocking

Plugins using the background service

The background data service is used by all of the sports scoreboard plugins (football, hockey, baseball/MLB, basketball, soccer, lacrosse, F1, UFC), the odds ticker, and the leaderboard plugin. Each plugin reads its own background_service block (under its own config namespace); check that plugin's config_schema.json for the keys it accepts.

Error Handling & Fallback

Automatic Retry:

• Exponential backoff (1s, 2s, 4s, 8s, ...)
• Maximum retry attempts configurable
• Logs all retry attempts

Fallback Behavior:

• If background service disabled: reverts to synchronous fetching
• If background fetch fails: returns cached data
• If no cache: returns empty/error state

Testing

# Check logs for background operations
sudo journalctl -u ledmatrix -f | grep "background"

Monitoring

View Statistics:

from src.background_data_service import get_background_service
from src.cache_manager import CacheManager

service = get_background_service(CacheManager())
stats = service.get_statistics()
print(f"Active: {stats['active_requests']}")
print(f"Completed: {stats['completed_requests']}")
print(f"Failed: {stats['failed_requests']}")

Other keys: total_requests, cached_hits, cache_misses, average_fetch_time, completed_requests_count (results currently held in memory) — see BackgroundDataService.get_statistics() in src/background_data_service.py.

Enable Debug Logging:

import logging
logging.getLogger('src.background_data_service').setLevel(logging.DEBUG)

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5. Permission Management

Ownership, modes, sudo rules and the repair scripts are listed in PERMISSIONS.md. This section covers the helpers code uses to keep files shareable.

Overview

LEDMatrix uses a dual-user architecture: the display service runs as root (hardware access), while the web interface runs as a non-privileged user. Centralized permission management ensures both can access necessary files.

Why It Matters

Problem:

• Root service creates files with root ownership
• Web user cannot read/write those files
• Results in PermissionError exceptions

Solution:

• Set group ownership to shared group
• Grant group write permissions
• Use setgid bit for automatic inheritance

Permission Utilities

from src.common.permission_utils import (
    ensure_directory_permissions,
    ensure_file_permissions,
    get_config_file_mode,
    get_assets_file_mode,
    get_assets_dir_mode,
    get_plugin_file_mode,
    get_cache_dir_mode
)

# Create directory with correct permissions
ensure_directory_permissions(Path("assets/sports"), get_assets_dir_mode())

# Set file permissions after writing
# (get_config_file_mode requires the file path — secrets files get a
# stricter mode than the main config)
config_path = Path("config/config.json")
ensure_file_permissions(config_path, get_config_file_mode(config_path))

When to Use Utilities

Use permission utilities when:

1. Creating new directories
2. Writing configuration files
3. Downloading/creating asset files (logos, fonts)
4. Creating plugin files
5. Writing cache files

Don't use for:

1. Reading files (permissions don't change)
2. Temporary files in /tmp
3. Files in already-managed directories (if parent has setgid)

Permission Standards

File Permissions:

File Type	Mode	Octal	Description
Config (main)	rw-r--r--	0o644	Owner write, all read
Config (secrets)	rw-r-----	0o640	Owner write, group read
Assets	rw-rw-r--	0o664	Owner/group write, all read
Plugins	rw-rw-r--	0o664	Owner/group write, all read
Cache files	rw-rw----	0o660	Owner/group write, no world access (_CACHE_FILE_MODE in src/cache/disk_cache.py)

Directory Permissions:

Directory Type	Mode	Octal	Description
All directories	rwxrwsr-x	0o2775	With setgid bit for inheritance

Note: The s in rwxrwsr-x is the setgid bit (2000), which makes new files inherit the directory's group ownership.

Common Patterns

Pattern 1: Creating Config Directory

from pathlib import Path
from src.common.permission_utils import ensure_directory_permissions, get_config_dir_mode

config_dir = Path("config/plugins")
ensure_directory_permissions(config_dir, get_config_dir_mode())

Pattern 2: Saving Config File

from src.common.permission_utils import ensure_file_permissions, get_config_file_mode

config_path = Path("config/config.json")
with open(config_path, 'w') as f:
    json.dump(data, f)
ensure_file_permissions(config_path, get_config_file_mode(config_path))

Pattern 3: Downloading Logo

from src.common.permission_utils import ensure_directory_permissions, ensure_file_permissions
from src.common.permission_utils import get_assets_dir_mode, get_assets_file_mode

logo_path = Path("assets/sports/nhl/logo.png")
ensure_directory_permissions(logo_path.parent, get_assets_dir_mode())
# ... download and save logo ...
ensure_file_permissions(logo_path, get_assets_file_mode())

Pattern 4: Creating Plugin File

from src.common.permission_utils import ensure_file_permissions, get_plugin_file_mode

plugin_file = Path("plugins/my-plugin/data.json")
with open(plugin_file, 'w') as f:
    json.dump(data, f)
ensure_file_permissions(plugin_file, get_plugin_file_mode())

Pattern 5: Cache Directory Setup

from src.common.permission_utils import ensure_directory_permissions, get_cache_dir_mode

cache_dir = Path("cache/plugin-name")
ensure_directory_permissions(cache_dir, get_cache_dir_mode())

Integration with Core Utilities

These core utilities already handle permissions - you don't need to call permission utilities when using them:

• ConfigManager - Handles config file permissions
• CacheManager - Handles cache file permissions
• LogoHelper - Handles logo file permissions
• PluginManager - Handles plugin file permissions

Manual Fixes

PERMISSIONS.md lists who owns what on an installed system, the expected modes, and which scripts/fix_perms/ script to run as which user. In short:

• fix_assets_permissions.sh, fix_cache_permissions.sh and fix_plugin_permissions.sh are run with sudo.
• fix_web_permissions.sh is run as the web interface user, without sudo (it refuses to run as root and calls sudo itself where needed). It resets project file ownership for that user, then makes the two helper scripts the web user may run as root (safe_plugin_rm.sh, safe_pip_install.sh) root-owned again and restores config_secrets.json to its owner, the ledmatrix group and mode 640. It does not write sudoers rules; scripts/install/configure_web_sudo.sh does that.

Do not chmod the whole config/ directory: config_secrets.json must stay 640.

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Related Documentation

• PLUGIN_DEVELOPMENT_GUIDE.md - Creating plugins with Vegas/on-demand support
• WEB_INTERFACE_GUIDE.md - Using on-demand controls in web UI
• PLUGIN_API_REFERENCE.md - Complete API documentation
• DEVELOPMENT.md - Development environment and testing