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Showing posts from March, 2020

Optimizing Embedded C - The Median Filter

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Optimizing code on desktop and mobile CPUs shares many of the same rules as embedded CPUs, but there are some important differences. In this post, I'm going to walk through optimizing an image filter on an ARM Cortex-M4/M7 processor. The specific code in this case comes from my work with the OpenMV project and optimizing their median filter. For those unfamiliar with their work, OpenMV has created a series of ever more powerful embedded CPU boards with integrated cameras for 'smart camera' IoT applications. The value they bring to the market is not only mating powerful embedded CPUs and advanced camera modules, but a rich software ecosystem. It has a large collection of useful native code primitives written in C, accessed through a Python front end. All of it is controlled from a slick IDE that makes experimentation and deployment painless. I started working with OpenMV a few months ago to optimize their time-critical functions. This week I've been working on their ima…