Add unified notification system #180
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This implements notification system inspired by seL4, with asynchronous
event delivery, notification masks, and IRQ fast-path optimization.
- Three-layer architecture: Basic/Async/Mask notifications
- IRQ fast-path delivery (5-10× faster than full IPC)
- Async queue with bounded RT processing
- Extended notification API with event_data payload
- Notification masks for multi-source event coordination
- TCB fields: notify_bits, notify_{data,pending,depth,generation}
- Softirq: ASYNC_SOFTIRQ for deferred notification delivery
- KDB: 'N' command for notification statistics
- IRQ subsystem: Dual delivery mode (IPC vs notification)
IRQ fast-path:
- IRQ_DELIVER_NOTIFY flag for notification-based delivery
- irq_handler_notify(): Fast-path handler (100-200 cycles target)
- IRQ encoding: 0-30 direct bit, 31+ uses bit 31 + event_data
- Safe thread lookup prevents use-after-free
Real-time properties:
- Bounded execution: NOTIFICATION_BATCH_SIZE = 4 events per softirq
- O(1) queue operations with atomic counter
- Memory barriers (DMB) for ordering guarantees
- WCET: 200 cycles for async delivery batch
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This implements notification system inspired by seL4, with asynchronous event delivery, notification masks, and IRQ fast-path optimization.
IRQ fast-path:
Real-time properties: