Operating Systems & Systems Programming Topics
Covers operating system fundamentals and systems programming topics, including process management, memory management, file system interfaces, inter-process communication, low-level kernel interactions, and system call interfaces (e.g., fork, exec, opendir, stat) across Unix/Linux and other OS environments.
Ring Buffers and Circular Data Structures
Discuss implementation and usage of ring buffers and other circular data structures in resource constrained systems. Topics include head and tail pointer management, modulo arithmetic or power of two masking, detection of full and empty conditions, zero copy patterns, and interactions with direct memory access. Cover single producer single consumer and multi producer patterns, lockless and wait free strategies, atomicity and memory ordering considerations, alignment and padding for cache friendliness, and recovery strategies for corrupted indices.
Real Time and Concurrency Patterns
Design patterns and practices for meeting timing constraints and coordinating concurrent activity in embedded systems. Topics include cooperative and preemptive scheduling models, task priority design, interrupt latency and mitigation strategies, deferred work and task offload, synchronization primitives such as mutexes and semaphores, priority inversion and priority inheritance, and lock free techniques where appropriate. Candidates should reason about worst case execution time, deadlines and jitter, trade offs between latency and throughput, and testing approaches for timing correctness. Also include safe coding patterns for interaction between interrupt context and thread context.
Timing Analysis and Worst Case Execution Time
Cover methods for analyzing timing behavior and proving worst case execution time guarantees in real time systems. Topics include static worst case execution time analysis and control flow and path analysis, measurement based validation using instrumentation and hardware timers, loop bound determination, and handling microarchitectural effects such as caches and pipelines. Explain interrupt latency sources, jitter analysis, how to build defensible timing margins, and how timing results feed into schedulability and deadline analysis for real time schedulers.
State Machines and Protocol Implementation
Explain how to design, document, and implement finite state machines for device drivers and communication protocols. Include state diagrams, table driven implementations, deterministic transitions, event queue handling, timeout and error recovery strategies, and memory efficient encodings of state. Cover parsing and framing, sequence handling, retransmission and flow control, and how state machines integrate with interrupts and deferred work. Describe testing approaches such as unit tests for state transitions, simulation, fault injection, and how to reason about corner cases and livelock or dead states.
Real Time Scheduling and Task Management
Explain scheduling and task management strategies for real time systems, including fixed priority scheduling and rate monotonic analysis, earliest deadline first scheduling, preemption costs, and context switch overhead. Discuss response time analysis, utilization bounds and safe operating points, handling of sporadic and periodic tasks, timer resolution, deferred work models, overload behavior and policies for deadline misses. Include practical RTOS considerations such as tick configuration, timer coalescing trade offs, and tuning priorities to meet latency and jitter requirements.
Embedded System Architecture and Decomposition
Translating product and hardware requirements into a maintainable firmware architecture and task decomposition. Discuss defining module boundaries and interfaces, choosing between bare metal, cooperative scheduling, or real time operating system approaches, designing inter task communication and synchronization, buffering and backpressure strategies, state machine driven control, testability and observability, and considerations for future scaling, updates, and maintenance. For senior candidates, justify architectural trade offs in terms of performance, reliability, testability, and development velocity.
Low Level Performance Optimization
Practical techniques for reducing CPU cycles, memory usage, and power on constrained hardware. Topics include algorithmic trade offs for worst case and average case behavior, memory layout and cache locality, code size reduction strategies, instruction scheduling and hot loop optimization, use of fixed point arithmetic, compiler and linker optimizations, profiling driven changes, and how to reason about when low level optimizations are necessary versus higher level algorithmic changes.
Interrupt Service Routine Design
Design and implement deterministic, low latency interrupt service routines that correctly handle hardware events without jeopardizing system responsiveness or safety. Candidates should discuss principles for keeping handlers lean, bounding worst case execution time, deferring expensive work to task level or deferred processing, and minimizing stack and memory usage in interrupt context. Explain safe communication patterns between interrupt context and application code including atomic operations, memory barriers, lock free queues, short critical sections with interrupts disabled briefly, and signaling mechanisms. Cover interrupt priorities, nesting, latency analysis, interactions with direct memory access, and handling priority inversion and reentrancy. Include testing and validation approaches such as measuring interrupt latency and worst case execution time on target hardware, instrumentation techniques, and static analysis as well as trade offs between determinism, throughput, and maintainability.