How to Detect and Prevent Race Conditions in Embedded Firmware

Background

Finding and eliminating hidden bugs in embedded development software is difficult because they often require complex debugging tools to trace observed symptoms back to their root causes.

Problem Description

Some errors remain invisible for long periods; the system may appear to run normally while a latent fault can corrupt data or code images. Rare anomalies are frequently dismissed as user errors, yet they persist as “ghosts” that are hard to reproduce.

Key Issues

1. Race Conditions

A race condition occurs when two or more execution threads (RTOS tasks, main(), or interrupt service routines) access shared resources in an interleaved order that changes the program’s behavior. Example: one thread increments a global counter while another resets it to zero. If the increment is not atomic, the final value can be corrupted.

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2. Non‑reentrant Functions

Non‑reentrant code is a special case of resource contention. Such functions may be called from different RTOS tasks indirectly through layers (socket → TCP → IP → Ethernet driver). If the driver accesses shared registers without protection, a pre‑emptive task can corrupt the operation, leading to lost packets or transmission errors.

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Best Practices

Use atomic operations or disable pre‑emption for critical sections, especially when ISR code competes for resources.

Create a dedicated mutex for each shared library or driver; acquire it before accessing any persistent data or hardware registers.

Adopt clear naming conventions (e.g., prefix global variables with g_) so shared objects are obvious during code reviews.

Prefer re‑entrant designs; avoid relying on compiler‑specific atomic guarantees.

When using GNU toolchains, link against the re‑entrant newlib C library instead of the default.

Conclusion

By staying vigilant, naming shared objects clearly, and protecting critical sections with mutexes or interrupt disabling, developers can prevent race conditions and non‑reentrant bugs that would otherwise cause intermittent, hard‑to‑debug failures in embedded systems.