Effective Work Sample Exercises for Hiring Top Firmware Engineers

Firmware engineering sits at the critical intersection of hardware and software, requiring a unique blend of technical skills that can be challenging to assess through traditional interviews alone. The firmware engineer's role is pivotal in product development, as they create the foundational code that directly interfaces with hardware components and enables device functionality. A poor hire in this position can lead to significant product delays, quality issues, and technical debt that may take months or years to resolve.

Work sample exercises provide a window into a candidate's actual capabilities beyond what their resume or verbal responses might suggest. For firmware engineers specifically, these exercises can reveal a candidate's coding style, debugging approach, system design thinking, and ability to optimize for constrained environments. By observing candidates working through realistic problems, hiring teams can better evaluate technical proficiency, problem-solving methodology, and attention to detail—all critical qualities for successful firmware development.

The exercises presented below are designed to assess different dimensions of firmware engineering expertise. They range from debugging existing code to planning system architecture, optimizing performance, and communicating technical concepts across teams. Each exercise simulates real-world challenges that firmware engineers face daily, providing authentic contexts for evaluation.

Implementing these work samples as part of your interview process will significantly improve your ability to identify candidates who not only possess the technical knowledge required but also demonstrate the practical skills and problem-solving approaches that lead to success in firmware development roles. Additionally, these exercises give candidates a realistic preview of the work they would be doing, helping ensure mutual fit and reducing early turnover.

Activity #1: Firmware Debugging Challenge

This exercise tests a candidate's ability to identify and resolve issues in existing firmware code—a critical skill for any firmware engineer. Debugging often constitutes a significant portion of a firmware engineer's responsibilities, requiring analytical thinking, systematic problem-solving, and attention to detail. This activity reveals how candidates approach troubleshooting and their familiarity with common firmware issues.

Directions for the Company:

• Prepare a small C/C++ firmware codebase (100-200 lines) for a simple embedded system function (e.g., reading from a sensor, controlling an LED pattern, or implementing a simple state machine).
• Introduce 3-5 deliberate bugs of varying difficulty:
• A syntax error
• A logical error (e.g., incorrect conditional logic)
• A timing/synchronization issue
• A memory management problem
• A hardware interface error
• Provide the candidate with:
• The buggy code
• A brief description of the intended functionality
• Documentation for any hardware interfaces referenced
• A development environment or online compiler where they can test their fixes
• Allow 45-60 minutes for this exercise.
• Have an experienced firmware engineer available to evaluate the solutions and provide feedback.

Directions for the Candidate:

• Review the provided firmware code and understand its intended functionality.
• Identify and fix the bugs in the code.
• Document each bug you find, explaining:
• The nature of the bug
• How you identified it
• Your approach to fixing it
• Any potential improvements to prevent similar issues in the future
• Be prepared to explain your debugging process and reasoning behind your solutions.
• You may use reference materials as needed, but the solutions should be your own work.

Feedback Mechanism:

• After the candidate completes the exercise, the interviewer should review their solutions and provide feedback on:
• One aspect of their debugging approach that was particularly effective
• One suggestion for how they could improve their debugging methodology or solution
• Give the candidate 10-15 minutes to implement the improvement suggestion on one of the bugs they fixed, observing how they incorporate feedback and adapt their approach.

Activity #2: Embedded System Architecture Design

This exercise evaluates a candidate's ability to design firmware architecture for a new embedded system—a skill that demonstrates their understanding of system-level thinking, hardware-software integration, and planning capabilities. Strong firmware engineers must be able to translate requirements into well-structured technical designs that account for hardware constraints and future scalability.

Directions for the Company:

• Create a specification for a moderately complex embedded system (e.g., a smart thermostat, a simple industrial controller, or a wearable health monitor).
• Include details about:
• The system's primary functions and requirements
• Available hardware components (microcontroller specifications, memory constraints, peripherals)
• Power requirements (battery-operated or mains-powered)
• Any communication protocols needed
• Future expansion considerations
• Provide the candidate with the specification document and any relevant datasheets.
• Offer a whiteboard or digital drawing tool for creating diagrams.
• Allow 45-60 minutes for this exercise.

Directions for the Candidate:

• Review the embedded system specification provided.
• Design a firmware architecture that meets the requirements, considering:
• Module organization and responsibilities
• Hardware abstraction layers
• Resource management (memory, processing, power)
• Error handling and recovery mechanisms
• Update/maintenance strategies
• Create a block diagram or flowchart illustrating your architecture.
• Prepare to explain your design decisions, including:
• Why you chose this particular architecture
• How it addresses the system requirements
• Trade-offs you considered
• How your design handles potential failure modes
• Be ready to discuss how your architecture could accommodate future enhancements.

Feedback Mechanism:

• After the candidate presents their design, provide feedback on:
• One strength of their architectural approach
• One area where their design could be improved (e.g., better resource utilization, more robust error handling, etc.)
• Ask the candidate to revise the specific portion of their design based on your feedback, giving them 10-15 minutes to make adjustments and explain their updated approach.

Activity #3: Real-time Firmware Optimization Challenge

This exercise assesses a candidate's ability to optimize firmware for performance and efficiency—a crucial skill for working with resource-constrained embedded systems. It reveals their understanding of low-level optimization techniques, memory management, and real-time constraints, as well as their ability to make appropriate trade-offs between different optimization goals.

Directions for the Company:

• Prepare a working but inefficient firmware routine (50-100 lines of C/C++ code) that performs a common embedded task (e.g., signal processing, data sampling and filtering, or a communication protocol implementation).
• Ensure the code has clear opportunities for optimization in areas such as:
• Processing efficiency (CPU cycles)
• Memory usage
• Power consumption
• Interrupt handling
• Provide the candidate with:
• The unoptimized code
• Specifications for the target microcontroller (including clock speed, memory constraints)
• Performance requirements (e.g., maximum execution time, memory budget)
• A development environment or simulator where they can test their optimizations
• Allow 45-60 minutes for this exercise.

Directions for the Candidate:

• Review the provided firmware routine and understand its functionality.
• Identify opportunities for optimization while maintaining the original functionality.
• Implement optimizations to improve the code's performance according to the specified constraints.
• Document your optimization strategy, including:
• What aspects of the code you chose to optimize and why
• The specific techniques you applied
• Quantitative improvements achieved (e.g., reduced execution time, memory usage)
• Any trade-offs made between different optimization goals
• Be prepared to explain how your optimizations would affect the overall system performance.
• You may use reference materials as needed, but the optimizations should be your own work.

Feedback Mechanism:

• After reviewing the candidate's optimized code, provide feedback on:
• One optimization technique they applied effectively
• One additional optimization opportunity they might have missed or a different approach they could have taken
• Give the candidate 10-15 minutes to implement the suggested additional optimization and explain how it further improves the code's performance.

Activity #4: Cross-functional Communication Simulation

This exercise evaluates a candidate's ability to communicate technical firmware concepts to non-technical stakeholders—an essential skill for effective collaboration in cross-functional teams. Firmware engineers must regularly translate complex technical details into understandable terms for product managers, hardware engineers, and other team members.

Directions for the Company:

• Prepare a scenario where a firmware issue is causing a product problem that affects multiple teams.
• Create a brief describing:
• The product and its primary function
• The observed problem from the user/customer perspective
• The underlying firmware issue (e.g., a timing problem, memory leak, or power management issue)
• The stakeholders involved (e.g., product manager, hardware engineer, quality assurance)
• Assign company representatives to role-play as different stakeholders with specific concerns:
• Product Manager: Concerned about timeline and feature impact
• Hardware Engineer: Questioning if it's a hardware or firmware issue
• Quality Assurance: Needing to understand how to test the fix
• Allow 30-45 minutes for this exercise.

Directions for the Candidate:

• Review the scenario and technical issue described.
• Prepare a brief (5-10 minute) explanation of:
• The root cause of the firmware issue in technical terms
• How this issue manifests as the observed product problem
• Your proposed solution approach and timeline
• Any trade-offs or risks associated with your solution
• Present your explanation to the cross-functional team (role-played by interviewers).
• Answer questions from each stakeholder, adapting your communication style to address their specific concerns and level of technical understanding.
• Be prepared to sketch diagrams or use analogies to help explain complex concepts.
• Focus on being clear, concise, and avoiding unnecessary technical jargon when communicating with non-technical stakeholders.

Feedback Mechanism:

• After the simulation, provide feedback on:
• One aspect of their communication that effectively bridged the technical-nontechnical gap
• One suggestion for improving their communication to better address stakeholder concerns
• Give the candidate 5-10 minutes to re-explain a portion of the technical issue or solution incorporating the feedback, observing how they adapt their communication approach.

Frequently Asked Questions

How long should we allocate for these work sample exercises?

Each exercise is designed to take 45-60 minutes, with an additional 15-20 minutes for feedback and improvement. If you're incorporating multiple exercises into your interview process, consider spreading them across different interview stages or limiting to 1-2 exercises per day to avoid candidate fatigue.

Should we use the exact exercises described, or can we customize them?

These exercises provide a framework that should be customized to match your specific product domain and technology stack. Adapt the scenarios, code examples, and technical requirements to reflect the actual work your firmware team does while maintaining the core assessment objectives of each exercise.

How do we evaluate candidates consistently across these exercises?

Create a structured scoring rubric for each exercise that evaluates both technical competency and process. For example, for the debugging exercise, score candidates on: number of bugs correctly identified and fixed, efficiency of debugging approach, quality of documentation, and responsiveness to feedback. Having multiple evaluators use the same rubric helps reduce individual bias.

What if a candidate doesn't complete the exercise in the allotted time?

Focus on evaluating the quality of work completed and the candidate's process rather than completion alone. A candidate who methodically solves two bugs with excellent documentation and explanation may demonstrate more valuable skills than one who rushes through all bugs with minimal explanation. Consider the candidate's approach and how they prioritized their time.

How can we make these exercises accessible for remote candidates?

For remote interviews, use collaborative coding platforms (like CoderPad or GitHub Codespaces) for the coding exercises and virtual whiteboarding tools (like Miro or Figma) for the design exercise. Ensure candidates have access to all necessary documentation and tools before the interview begins. For the communication exercise, conduct it via video conference with clear role introductions.

Should we provide these exercises to candidates in advance?

For the debugging and optimization exercises, providing the problem statement 24 hours in advance can allow candidates to familiarize themselves with the context without compromising assessment value. The architecture design and communication exercises are better conducted live to evaluate real-time thinking and adaptation skills.

Implementing these work sample exercises will significantly enhance your firmware engineer hiring process, providing deeper insights into candidates' technical abilities, problem-solving approaches, and communication skills. By observing how candidates tackle realistic challenges, you'll be better equipped to identify those who will excel in your specific firmware development environment.

For more comprehensive hiring resources, check out our AI Job Description Generator, AI Interview Question Generator, and AI Interview Guide Generator. These tools can help you create a complete, structured hiring process that consistently identifies top firmware engineering talent for your organization.

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