Interviewing for an embedded system engineer role? You’ll want to be prepared to answer a wide range of technical questions. Embedded systems combine software and hardware to perform a specific function, so expect questions that dig into your skills in both areas.
This article will list some of the most common and difficult interview questions you might be asked as an embedded system engineer. You’ll be able to show off your skills and stand out from the others if you prepare well. Let’s dive in!.
Explaining Embedded Systems
To start, interviewers want to assess your foundational knowledge. Get ready to explain what an embedded system is and what its most important features are.
- Performs a dedicated function, often in real-time
- Constraints like limited memory, power, or processing resources
- Integrated hardware and software components
You might also be asked to list the most important parts of a normal embedded system:
- Microcontroller or microprocessor
- Memory (RAM, ROM)
- Peripherals and interfaces (ADC, GPIOs, communication buses)
- Power supply
- Input/output devices
When explaining embedded systems, use specific examples like a digital watch, car engine control unit, or GPS navigator. This shows an depth understanding.
Embedded Programming Languages
As an embedded software engineer, your choice of programming languages is crucial. C and C++ are the most common languages used due to their performance and low-level control. Be ready to discuss:
- Why C is well-suited for embedded systems (compact, hardware access, portable)
- C++ features like classes, templates, and exceptions for embedded use
- Other languages like Rust, Go, and Ada and their tradeoffs
Know which language you have the most experience with, and what types of projects you’ve used it for. Mention any specialized tools or libraries you’re familiar with as well.
Hardware Platform Knowledge
You’ll need be well-versed in popular embedded hardware architectures and components. Common questions include:
- Explaining the key features of platforms like ARM Cortex-M, RISC-V, AVR, PIC, and MIPS.
- Discussing memory technology tradeoffs (Flash, EEPROM, SRAM)
- Understanding peripheral interfaces like UART, SPI, I2C, USB
- Leveraging sensors, ADC, DAC, PWM, and other I/O devices
For bonus points, speak to specific microcontrollers you’ve worked with, and the types of products you’ve designed with them.
Handling Concurrency and Real-Time Requirements
A key embedded software skill is managing concurrency and real-time behavior. Be ready for questions like:
- Implementing pre-emptive vs cooperative multi-tasking
- Using RTOSes and schedulers to handle task switching
- Avoiding race conditions with semaphores, mutexes, and resource locking
- Meeting hard real-time deadlines and constraints
Have code examples ready from past projects where you handled these challenges successfully.
Optimizing Performance and Efficiency
Embedded systems have tight resource limitations Expect questions on how you’ve optimized
- Memory usage through stack management, dynamic allocation
- Code efficiency with loops, functions, and data structures
- Power consumption via clock gating, sleep modes
- Execution speed by reducing cycles and instructions
Being able to quantify optimizations with metrics or anecdotes is impressive
Debugging and Testing Techniques
Bugs take on new meaning in embedded devices where crashes can have serious consequences. Be ready to discuss:
- Debugging via JTAG, print debugging, and simulators/emulators
- Unit testing modules and interfaces
- Integration testing via test benches and test suites
- Monitoring with profiling tools and logic analyzers
Share war stories showcasing your tenacity for squashing those hard-to-find bugs!
Productizing and Manufacturing Considerations
The interview may go beyond pure engineering topics. Additional areas to study up on:
- Design for manufacturing – component selection, design rules, tolerances
- Lifecycle management – upgrades, maintenance, end-of-life
- Supply chain logistics – sourcing parts, inventory, lead times
- Compliance testing – FCC, CE, UL, other regulatory bodies
Even a few points on these topics demonstrates you consider the full lifecycle of a product.
Behavioral and Soft Skills
In additional to technical expertise, hiring managers look for engineers who:
- Communicate well through documentation and diagrams
- Collaborate effectively across teams
- Prioritize tasks and manage time wisely
- Continuously improve and learn new skills
Have stories ready highlighting your soft skills and what you bring to the team beyond just technical ability.
Questions to Ask the Interviewer
The interview is also a chance for you to assess the company. Prepare some questions like:
- What types of products and projects will I be working on?
- How do you balance innovation vs. robustness in your designs?
- What tools and workflows do you use for development and testing?
- How does the team incorporate feedback from manufacturing?
- What opportunities are there for training, growth, and advancement?
This shows your interest in the role and learning more about their engineering practices.
Preparing for an embedded systems engineering interview takes dedication. Study core concepts, hone your skills with hands-on projects, and research the company. With the techniques covered here, you’ll demonstrate your technical abilities and be ready to hit the ground running on innovative embedded designs. Best of luck with your interview! Let us know if you have any other embedded system interview questions we should add to our list.
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Questions and answers sent in will be looked over and edited by Toptal, LLC, and may or may not be posted, at their sole discretion.
Toptal sourced essential questions that the best embedded software engineers can answer. Driven from our community, we encourage experts to submit questions and offer feedback.
Describe the pros and cons of using a generic real-time operating system (RTOS) on a mid-range microcontroller.
RTOSes can significantly ease the development of complex products, which can translate into faster development cycles. They usually allow separating code into tasks and help tasks talk to each other. They also usually have “drivers” for platform-specific hardware, which makes moving firmware to new hardware easier. While doing all of that, they also add extra code and CPU use, which is not good for all projects. 2 .
What are some common issues when handling interrupts?
Depending on the device and application, interrupt handlers almost always need to finish their work quickly. This makes it harder for them to do complex things in their code. Also, the hardware or software environment in which the interrupt handler code is run may make it impossible for the interrupt handler code to use:
- Common library functions
- Access to peripherals and devices
- Even certain types of CPU instructions
Most of the time, this problem can be fixed by having the interrupt controller set a special variable that non-interrupt code can then use to do whatever it wants 3
In platforms with significant constraints on memory size, is it more preferable to allocate memory statically or dynamically?
It’s preferable to use static memory allocation on platforms with memory sizes in the low kilobytes and below. This is because data overhead, CPU overhead, and memory fragmentation can be big problems when dynamic memory allocation is used.
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Why are C and C++ still very popular and widely supported in embedded firmware development?
Hardware constraints, both for memory sizes and CPU speed, limit what can be done on embedded devices. When it comes to abstractions, C and C usually have very little overhead and are very “close to the hardware.” This makes them suitable for even the smallest devices. 5 .
How many wires are required to reliably implement TTL-like serial communication between two devices, and why?
Serial communication that works like TTL is often used to connect small microcontroller-based devices to bigger computers, either for general communication or to upload firmware. This type of communication uses two wires, one for each direction, called TX (transmit) and RX (receive. For TTL serial communication to work, there must also be a shared electrical ground level between the devices. This means that at least three wires are needed. (The requirement for common electrical ground is also present in I2C and SPI. ) 6 .
Since 32-bit and 64-bit microcontrollers exist, why are 8-bit ones still in use?
The general reason is picking the right tool for the job. The three most common reasons are backwards compatibility, price, and electrical power consumption. When connecting to existing systems, backwards compatibility is very important. This is especially true in industrial settings, where electrical and operational limitations often limit the microcontrollers that can be used.
Generally, smaller microcontrollers (with narrower primary registers) are also cheaper. But they can have a lot of different peripherals and interfaces, so they can be used in many situations where advanced features are needed but not a fast CPU.
Smaller microcontrollers also generally require less power to operate, which is especially important for IoT and battery-powered devices. 7 .
Is firmware and data embedded in microcontrollers generally safe from downloading, tampering, or hacking?
No. Any code and data uploaded to a microcontroller should be pretty easy to download and change, unless the microcontroller was built in a way that makes it impossible to download and/or change firmware. (Such hardened microcontrollers are usually expensive. ) 8 .
Describe the role of a watchdog timer.
Many microcontrollers have a watchdog timer, which is usually made with special hardware that can be used to see if the software that is running on the microcontroller got stuck.
Microcontrollers are designed to be sturdy and resilient. But there’s still any number of issues that can affect hardware stability. There can also be an unhandled combination of events on the software side. Both of these can cause microcontrollers to “hang,” either electrically or in an infinite loop in software.
A watchdog timer is a part of the system that needs to be told by the software that everything is working as it should within a certain amount of time. If the watchdog doesn’t get the message it’s looking for, it will do something, like reset the microcontroller or even the whole thing. This is normally done on a regular basis, and the watchdog timer will do what it needs to do if it doesn’t get a notification after a set amount of time has passed since the last notification. 9 .
Which of the following are the most important things about UART-based (also called RS-232-like and TTL-like) serial communication, I2C communication, and SPI communication?
Simple UART-based serial communication, with or without UART hardware, is the easiest communication protocol to set up, but it has a lot of problems:
- It’s intended to connect only two devices.
- It is asynchronous, which means that the devices don’t agree on the clock rates.
- A slow bit rate (up to 115,200 bps) is where it’s most often used.
I2C can connect up to 127 devices on the same electrical bus, and each device is individually addressable. A “master” device makes a clock signal that all the other devices, which are called “slave devices,” can use. There is only one data wire, so all communication is unidirectional. (It’s commonly used to communicate with sensors on a PCB, which often use simple request-response protocols. ).
It’s made so that complex devices can talk to each other quickly and both ways. For example, a lot of data can be sent at once using the SPI bus. With SPI, the data and clock wires are shared by all devices. However, each device has its own addressing wires that let it talk to and from other devices. 10 .
Discuss a couple of options for wireless communication between embedded devices.
At the high end of the cost and difficulty scale, one of the wifi standards can be used to set up wireless communication. These offer great bandwidth, are interoperable with many other devices, and can be long-range. But wifi standards are also fairly complex and require dedicated hardware.
Bluetooth is a reasonable choice for interfacing between different types of hardware over short distances, i. e. , those of up to 15 yards (~14 meters). It also requires specialized hardware, but such hardware is usually cheap and simple to use. Devices using Bluetooth for communication often emulate a serial line between them.
Aside from WiFi and Bluetooth, there are also radio-based devices and protocols that work on the same frequencies (around 2 4 GHz), but with simpler protocols that are incompatible with the standard ones. They are usually cheaper than Bluetooth and simpler to implement.
There are also transceivers operating at low frequencies such as 433 MHz. They have very low bit rates over short distances (up to 9 meters or 10 yards), but they are very cheap and easy to set up. Solutions like LoRa, SigFox, and NB-IoT can be used if longer ranges are needed but a low bitrate is fine. This is often the case with IoT devices.
Finally, infrared communication over very short distances (a couple of yards) can also be an efficient choice.
There is more to interviewing than tricky technical questions, so these are intended merely as a guide. Not every good candidate for the job will be able to answer all of them, and answering all of them doesn’t mean they are a good candidate. At the end of the day, hiring remains an art, a science — and a lot of work.
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