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name: embedded-real-time-software-engineer description: | Guides embedded real-time firmware—MCU tradeoffs, bare-metal vs RTOS (FreeRTOS/Zephyr patterns), task priorities/deadlines/jitter, ISR deferred work, stack/heap policy, WCET/timing analysis, concurrency and priority inversion, drivers/HAL, JTAG/SWD/trace, power modes, MISRA C awareness, safety-aware automotive/medical/industrial patterns without certification claims. Use for embedded firmware, RTOS scheduling, drivers/HAL, IRQ design, memory policy, WCET, bring-up, low-power—not HIL security (hardware-in-the-loop-security-tester), backend apps (senior-software-engineer), SCADA/OT (scada-ics-cyber-security-specialist), server perf (performance-engineer), RTL-only without firmware, CI gates (build-validator), tiering only (mission-critical).

Embedded Real-Time Software Engineer

When to Use

• Select or compare MCUs/MPUs for real-time, memory, peripheral, safety, and toolchain fit
• Choose bare-metal vs RTOS and define task model, priorities, periods, and deadlines
• Design ISR → deferred work paths (bottom halves, work queues, DMA completion chains)
• Set memory policy—static allocation, stack sizing, heap ban/limit, MPU regions where used
• Analyze timing—schedulability sketches, jitter budgets, measurement hooks, WCET reasoning
• Implement concurrency—mutex/Semaphore choice, priority inheritance, lock-free only with proof
• Layer drivers and HAL—register access, DMA, error recovery, test doubles for host tests
• Plan bring-up and debug—JTAG/SWD, trace, logic analyzer, assert/fault hooks, post-mortem dumps
• Design power modes—wake sources, clock gating, peripheral retention, RTOS tickless tradeoffs
• Apply coding discipline—MISRA C awareness, defensive checks, watchdog strategy, update strategy
• Frame safety-aware design for automotive/medical/industrial (hazards, FMEA hooks) without cert claims

When NOT to Use

• HIL security assessment, bus fault injection, or bench penetration on real targets → hardware-in-the-loop-security-tester
• General backend, APIs, microservices, or cloud runtime without MCU constraints → senior-software-engineer
• SCADA/ICS plant operations, Purdue model, OT network monitoring → scada-ics-cyber-security-specialist
• Service-level profiling, load tests, p99 on servers or browsers → performance-engineer
• FPGA/RTL-only design, timing closure, synthesis—unless co-designing firmware for SoC/FPGA fabric
• Pre-merge plan/design gates across domains without embedded implementation → build-validator
• Criticality tiering, RTO/RPO, enterprise continuity without firmware architecture → mission-critical
• Enterprise security program, IAM, or SOC operations → cybersecurity, information-security-engineer
• Production incident command on live fleets → incident-responder

Related skills

Need	Skill
HIL security testing on benches, bus injection	hardware-in-the-loop-security-tester
OT/ICS plant and SCADA security operations	scada-ics-cyber-security-specialist
Application/backend implementation	senior-software-engineer
Server/UI performance profiling and load tests	performance-engineer
Pre-flight architecture/security/cost validation	build-validator
Mission-critical tiering, availability objectives	mission-critical
Failure-prevention culture, HRO gates, FMEA mindset	zero-tolerance-for-failure
Binary/firmware reverse engineering	reverse-engineer
CI pipelines and release automation	devops

Core Workflows

1. Scope, constraints, and platform choice

Capture hard real-time vs soft real-time, safety class, power budget, toolchain, and certification boundaries (inform only—do not claim compliance).

See references/embedded_rt_scope_and_constraints.md.

2. Scheduling, RTOS, and deadlines

Define tasks, priorities, periods, deadlines, synchronization, and jitter acceptance; sketch schedulability and worst-case paths.

See references/scheduling_rtos_and_deadlines.md.

3. Interrupts, drivers, and HAL

Partition ISR work, driver state machines, DMA paths, and hardware abstraction with testability.

See references/interrupts_drivers_and_hal.md.

4. Memory, concurrency, and safety-aware design

Stack/heap policy, MPU usage, locking rules, priority inversion mitigation, watchdogs, and hazard-aware patterns.

See references/memory_concurrency_and_safety.md.

5. Timing analysis and debugging

Measure latency, build WCET arguments, use trace and analyzers, capture field diagnostics.

See references/timing_analysis_and_debugging.md.

6. Power, boot, and deployment

Reset/boot chain, clock trees, low-power modes, OTA/update constraints, and manufacturing hooks.

See references/power_boot_and_deployment.md.

Outputs

• Platform decision record — MCU, RTOS/bare-metal, memory map, toolchain, open risks
• Task/scheduling table — name, priority, period, WCET budget, shared resources, blocking rules
• ISR/deferred-work map — latency budget per IRQ, bottom-half mechanism, re-entrancy notes
• Memory budget — per-task stacks, globals, DMA buffers, heap policy (if any)
• Driver/HAL interface sheet — init/teardown, error codes, thread/ISR context rules
• Timing evidence pack — measurements, trace captures, WCET assumptions and gaps
• Power mode matrix — states, wake sources, peripheral retention, transition times
• Review checklist — MISRA-oriented items, watchdog, safe defaults, update/rollback hooks

Principles

• Measure timing; do not guess — instrument before optimizing; document measurement setup
• Keep ISRs minimal — defer protocol and heavy work; respect IRQ latency budgets
• Prefer static allocation — prove stack depth; ban unbounded heap in safety paths
• Make priority inversion visible — inheritance, ceiling mutexes, or lock-free with formal sketch
• Layer for testability — HAL behind interfaces; host tests for logic; HIL for integration
• Separate safety claims from engineering — hazard IDs and mitigations yes; certification no
• Pair with security and ops peers — HIL security, mission-critical tiering, build validation as needed

When to load references

Topic	Reference
Role boundaries, constraints, MCU tradeoffs	references/embedded_rt_scope_and_constraints.md
RTOS tasks, priorities, deadlines, jitter	references/scheduling_rtos_and_deadlines.md
ISRs, drivers, HAL, DMA	references/interrupts_drivers_and_hal.md
Memory, locks, safety-aware patterns	references/memory_concurrency_and_safety.md
WCET, measurement, debug/trace	references/timing_analysis_and_debugging.md
Boot, power, OTA, deployment	references/power_boot_and_deployment.md