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Simple Events Example

A very basic example of using events and event queues to decouple modules in embedded systems. This example is based on the code presented by Matt Chernosky in, but extends it into a complete executable example with unit tests.

The interesting thing about this example that none of the unit tests require any mocks to execute (well, mostly--the tests for the executive include some fake functions that are something like mocks). The need for mocks is a sign that you have a tight coupling between modules. Here, the event queue breaks that coupling. It also gives you a uniform way to manage interrupts, handle events from multiple sources, and to implement a system that sleeps between interrupts. The tradeoff is that you have a somewhat more complex system than you'd get with direct function calls, and you lose some static type-safety guarantees.

Real-world examples of queue-based decoupling in small embedded systems include the Quantum Platform, and the TinyOS task management system.

Caveat: This is not production-ready code (in particular, it doesn't include concurrency protection--such as interrupt disabling or mutexes--around queue actions). But you could easily build a production-ready system from this starting point.


Uses the Ceedling suite for unit testing, and also to manage the build of the example main.c. You'll need to install Ceedling, and execute ceedling new SimpleEventExample (say no to overwriting project.yml), to run the tests.

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