My wife is a preschool teacher, and she is a master of reuse. When I see a toilet paper roll is used up, I think of tossing that tube in recycling. But to her, that tube is a versatile component that still has much to give and should be stockpiled. When she starts a project, she turns to her vast collection of tubes, jars, buttons, felt, cardboard, pipe cleaners and paper. Then the creativity starts and these components combine to produce some cute little craft. I do get jealous of her ability to look at a forgotten torn egg crate and envision the caterpillar it will evolve into.
I am also a fan of reuse, although I can’t compete with her creativity. My philosophy is, “Why reinvent the wheel if I can reuse something that already does the job?” During application development, code reuse is one of the major benefits and attractions for using open-source software. When developing application-specific software, our time and innovation should be spent on that which will differentiate; not on the common building blocks and components that are already available. In the analogy with my wife, we want to create the ‘caterpillar’, not the egg crate. But a major question with code reuse, particularly when that code originates elsewhere, is “Can we depend on it?” Especially when these ‘caterpillars’ need go to production, we have concerns about the quality of the reused code, how vetted it is and whether or not it will it be stable.
This is where NXP’s MCUXpresso software development kit (SDK) can help. This SDK is a software package specific to NXP’s EdgeVerse™ platform of microcontrollers, containing peripheral drivers, connectivity stacks and other middleware. NXP delivers software reliability through high-quality production-grade software in this SDK. For example, drivers and startup code are MISRA-C compliant and checked with Coverity® static analysis tools. NXP also checks SDK runtime tests on a vast board farm, using development boards of the different product families supported. Every night, the latest SDK code runs on the boards, logging any issues introduced in recent code changes. Today, these tests run on 46 platforms and run over 80,000 test cases. Also, this SDK code base is well vetted in production through our many customers and their end products, with more than 360,000 downloads globally.
The open-source Zephyr OS also benefits from code reuse. The Zephyr Project was conceived to provide a new RTOS option and has developed a vibrant, active community continually contributing new code. Learn more about what makes Zephyr unique at the blog post “Zephyr OS LTS 2 Release Adds Full Platform Support for i.MX RT600 Crossover MCUs”. But the Zephyr Project also integrates other open-source modules, for those instances when the wheel does not need to be reinvented and code reuse can be leveraged.
For example, Zephyr OS integrates LVGL for graphics,Mbed TLS crypto library and MCUboot for secure bootloader and firmware updates. In addition, NXP’s product portfolio strongly aligns with Zephyr OS and NXP is one of the founding members of the Zephyr Project. NXP is committed to Zephyr, and contributes to the Project by upstreaming code to the Zephyr repository. Much of this code is focused on enabling Zephyr OS and its features on NXP hardware, and the foundation of that hardware support is reused from MCUXpresso SDK. NXP also contributes by testing Zephyr releases on the same board farm used to test the SDK. Today over 5000 Zephyr test cases are run on 17 platforms in the board farm.
Zephyr OS provides a set of drivers for common hardware-related features, like Flash and UART drivers. These Zephyr drivers are written to be hardware agnostic and enable Zephyr applications to easily port across the supported hardware platforms. These Zephyr drivers are built on a hardware abstraction layer (HAL), illustrated in the figure below. NXP’s HAL is comprised of the peripheral drivers and device support directly from the MCUXpresso SDK. That code reuse delivers all the same quality from the testing and production use (discussed earlier), providing a robust and proven foundation for the HAL.
Looking at a specific example, below are the Zephyr software layers including the hardware platform support for the i.MX RT1060 MCU. The i.MX RT1060 uses external flash connected to the FlexSPI peripheral. The low-level FlexSPI driver is the same driver from the MCUXpresso SDK. On top of this, NXP upstreams a shim driver into the Zephyr repository, which directs Zephyr’s hardware-agnostic memory APIs, like the Flash driver, to the MCUXpresso SDK drivers that directly control the peripheral. This builds the NXP HAL on top of the SDK drivers, and then the Zephyr kernel, drivers and upper layers all build on top of that HAL.
To better experience, download the block diagram.
The MCUXpresso SDK code reuse in Zephyr OS provides additional benefits beyond quality. Improvements and features added to the SDK drivers can be quickly and easily integrated into a Zephyr application. If bugs are found in these drivers, whether by Zephyr users or other NXP users, the bug fixes in the MCUXpresso SDK can be rapidly up-streamed to benefit all Zephyr users. Plus, sharing the same underlying MCUXpresso SDK HAL enables easier portability for Zephyr across the NXP portfolio, including NXP devices supported by the SDK, but not yet included in the Zephyr Project – meaning the SDK reuse also enables a software migration path to Zephyr (for non-Zephyr applications already using MCUXpresso SDK). If the developer of that existing application wants to evaluate with Zephyr OS, they can continue using the same MCUXpresso drivers and focus their porting efforts on adopting Zephyr OS and its features. The Zephyr application can be built using the same direct APIs into the SDK drivers. Porting to the general Zephyr drivers is not required and could even be done later if desired.
The Zephyr Project and code reuse of MCUXpresso SDK drivers help jump-start embedded application development so that developers can focus on the end application and benefit from the existing robust HAL. Plus, the high-quality production-ready code provided by the SDK provides confidence in the software. So the next time you develop a caterpillar, and you want to reuse an existing and reliable egg crate, consider all the code reuse and benefits offered by the Zephyr Project with NXP MCUXpresso SDK.
Visit our last blog Zephyr OS LTS 2 Release Adds Full Platform Support for i.MX RT600 Crossover MCUs
Derek Snell has been focused on supporting NXP micro-controllers since 2008. He has spent that time supporting customers, writing examples and application notes, creating trainings, improving software and enablement, and optimizing MCU power and performance. A graduate of Rose-Hulman Institute of Technology, he currently resides in Indianapolis, Indiana.
