Course Outline: Embedded Real-Time Software

Part 1: Real-Time Operating Systems (RTOS)

Embedded Systems Overview: Definition and characteristics of embedded systems. * Real-Time Concepts:
- Definition of Real-Time Systems (correctness depends on time).
- Hard vs. Soft Real-Time: Distinction based on the consequences of missed deadlines.
- Constraints: Processor speed, memory, energy, and concurrency.
RTOS Fundamentals:
- Comparison between General Purpose OS (GPOS) and RTOS.
- Key Characteristics: Reliability, Predictability, Performance, Compactness, Scalability.
- Task Model:
  - Task types: Periodic (time-driven), Aperiodic (event-driven, one-shot), and Sporadic (event-driven with minimum inter-arrival time).
  - Task States: Running, Ready, Blocked, Suspended.
  - Task Control Block (TCB): Data structure for managing task context.

Task Specification:
- Temporal parameters: Release time, Execution time ( $e_{i}$ ), Deadline ( $D_{i}$ ), Period ( $p_{i}$ ).
- Functional parameters: Criticality and Preemptivity.
Scheduling Algorithms:
- Clock-Driven Scheduling: Static schedules, cyclic executives, frame-based scheduling.
- Priority-Based Scheduling:
  - Fixed Priority: Rate Monotonic (RM) scheduling (shorter period = higher priority).
  - Dynamic Priority: Earliest Deadline First (EDF) scheduling (earlier deadline = higher priority).
Schedulability Analysis:
- CPU Utilization ( $U = \sum e_{i} / p_{i}$ ).
- Necessary and sufficient conditions for schedulability under RM and EDF.
- Worst-Case Execution Time (WCET) estimation.

Resource Sharing:
- Shared data structures, memory, and I/O.
- Race Conditions: Issues arising from interleaved execution.
- Critical Sections: Code segments accessing shared resources requiring mutual exclusion.
Priority Inversion:
- Problem: High-priority task blocked by low-priority task holding a resource.
- Unbounded Priority Inversion: Infinite blocking due to medium-priority tasks.
- Protocols:
  - Priority Inheritance Protocol (PIP): Boosting priority of the blocking task.
  - Priority Ceiling Protocol (PCP): Preventing deadlocks and bounding blocking time using resource ceilings.
Synchronization Primitives:
- Semaphores: Binary and Counting semaphores for signaling and resource counting. * Mutex: Mutual exclusion objects with ownership and priority inheritance capabilities.
- Condition Variables: Signaling state changes between threads.
- Atomic Variables: Uninterruptible operations for lock-free synchronization.
Inter-Task Communication:
- Message Queues: Asynchronous data transfer (FIFO).
- Pipes: Byte-stream data transfer.

Fault Analysis:
- Types of bugs: Permanent, Aging-related (memory leaks), and Heisenbugs (disappear when probed).
- Cost of fixing bugs at different development stages.
Debugging Tools & Techniques:
- GPIO Debugging: Using physical pins to measure timing/state without halting.
- Logging/Printf: Non-intrusive tracing (limitations in timing).
- JTAG/SWD Debuggers: Breakpoints, stepping, and memory inspection.
- Tracing: Recording execution history (system events, ISRs) for performance analysis (e.g., Segger SystemView).
Testing:
- Unit Testing in Zephyr (Ztest framework).
- Code Coverage: Statement, Decision, and MC/DC coverage.