Introduction
Firmware is rarely glamorous, but it is often the reason products fail in the field. From random lockups to battery drain and missed deadlines, the most damaging issues usually stem from common, avoidable mistakes, not obscure technical edge cases. Whether you’re building a one-off prototype or production-ready firmware, understanding these pitfalls early can save time, money, and repudiation. In this post, we’ll break down the most frequent development traps and how to steer clear of them.
Blocking Calls in Time-Critical Code
One of the most damaging mistakes in embedded systems is placing blocking calls, like sleep() or long polling loops, in time-critical sections such as Interrupt Service Routines (ISRs), control loops, or real-time threads. Even though these functions might seem harmless during early testing, they can introduce subtle timing issues, missed events, or total system hangs once the system scales or interacts with real-world inputs. In worst case scenarios, they can cause unpredictable behaviour that’s difficult to reproduce or debug, especially when multiple subsystems start competing for CPU time or peripheral access.
In order to avoid messing with time-critical code, time-sensitive code should be designed to be non-blocking and event-driven. In ISRs, do the bare minimum: set a flag, push data to a queue, or signal a task, and exit immediately. Use timers, interrupts, and state machines to manage delays or sequence instead of busy loops. If you’re using an RTOS, rely on synchronization primitives like semaphores or message queues with timeouts rather than spinning in place.
Poor Use of Interrupts
As mentioned before, interrupts are essential for responsive embedded systems, but when misused, they become one of the most difficult problems to diagnose and fix. Examples of misuses include overloading ISRs with too much logic, calling non-reentrant functions, introducing hidden dependencies between interrupts, or using interrupts during ultra-time-sensitive code where every cycle matters. All of these can lead to timing-sensitive bugs that appear intermittently that often happen under specific conditions or after a long runtime. Also, improper priority configuration or unbalanced nesting can cause missed events, priority inversion, or even lockups.
You can avoid these issues by keeping ISRs as short and deterministic as possible. You can do this by ideally acknowledging the interrupt and deferring work to the main loop or a lower priority task via flags, queues, or semaphores. Avoid calling complex logic, dynamic memory, or blocking functions (as mentioned above) from within an ISR. It is imperative to use interrupt priorities deliberately to ensure critical tasks are serviced appropriately without starving the system. For ultra-time-sensitive code, interrupts could be disabled around the sensitive code, then re-enable immediately. Basically, a disciplined and minimalist approach to interrupt design builds stable and maintainable firmware!
Lack of Error Handling
Sometimes, firmware is built on the optimistic assumption that things will “just work.” But in the real embedded world, things like hardware glitches, timing hiccups, or rare edge cases can and will cause things to fail. Without proper error handling, these failures often go undetected, leading to silent data corruption, frozen devices, bricked devices or erratic behaviours that are difficult to trace. And the worst part is some of these issues don’t surface until devices are in the field where diagnosing and recovering from them becomes exponentially more expensive and time-consuming.
This is why it is important to treat every function call, especially those interacting with hardware, as a potential failure point! Helpful error handling techniques include checking return values, validating assumptions, and implementing fallback behaviour where possible. Assert mechanisms or lightweight logging can also be really useful to flag unexpected states during development. When considering production firmware, you should consider implementing structured error codes or a central error handler that can log, recover, or escalate issues safely when necessary. Designing your system to fail gracefully is also very important for robustness so consider adding timeouts, retries and watchdogs when possible. The goal should always be to develop systems that can detect and respond to failure for robustness rather than hoping failures won’t happen.
Skipping Unit Testing or CI
In many firmware teams, testing is still manual and hardware-dependent where developers flash a build, push some buttons and declare success. But without automated unit tests or Continuous Integration (CI), there’s no safety net. Bugs that were fixed once can quietly return, changes in one module can break another, and developers lose confidence in the stability of the codebase. Over time, this lack of test infrastructure slows down development speed, increases fear of change and turns releases into high-stress events. This could really be a killer of quality and team morale.
Having this in mind, it is important to start early with unit testing and CI. You can introduce unit tests for core logic that doesn’t depend on hardware like state machines, protocol handlers, math functions, etc. Lightweight frameworks like Ceedling or Google Test are perfect for unit testing especially if your code is portable. Then, the unit tests can be integrated with a CI system (like GitHub Actions, GitLab CI, Jenkins) to automate and run them on every push or pull request.
Conclusion
Firmware development comes with its own unique set of challenges. Whether it’s blocking calls that kill real-time performance, silent failures due to missing error checks, or not leveraging testing, many of the most painful issues stem from common, avoidable mistakes. The good news? Recognizing these pitfalls early can make all the difference.
If you are working on a project and looking for support to get started on your firmware project with the right foot, Dojo Five is here to help! Book a call with us to get the conversation started. We look forward to hearing from you! Or if you’re into DevOps, you can sign up for our EmbedOps platform. We look forward to hearing from you!