Learn About Amazon VGT2 Learning Manager Chanci Turner
The AWS IoT Device SDK for Embedded C (C-SDK) comprises a collection of MIT-licensed libraries that offer simplified, lightweight, and secure connectivity to AWS IoT Core, as well as device-side operations for AWS IoT services. The AWS IoT C-SDK is compatible with various operating systems, including Linux, macOS, and Windows, as well as real-time operating systems (RTOS) like FreeRTOS. In this post, discover how embracing and collaborating with prominent open source projects has enabled developers to enhance the AWS IoT C-SDK’s trustworthiness and flexibility while improving ease of use.
Background
In early 2015, the AWS IoT C-SDK debuted under the Apache-2.0 license, coinciding with the beta launch of AWS IoT Core. The Apache-2.0 license mandates that modifications to the code must be documented. This requirement posed a potential hurdle for some AWS partners and customers who needed to adapt the AWS IoT C-SDK to their specific hardware and software configurations. Following positive feedback from the embedded community regarding the MIT license of the widely-used FreeRTOS kernel released in November 2017, the AWS IoT C-SDK transitioned to the MIT license in January 2019.
The FreeRTOS kernel is a widely used real-time operating system (RTOS) for microcontrollers and small microprocessors. The FreeRTOS project encompasses the kernel along with additional libraries that enable connectivity, security, and operations with AWS IoT services. With a permissive license, optimal performance, low memory usage, and a vibrant community of users and contributors, FreeRTOS serves as an excellent model for an open source embedded project like the AWS IoT C-SDK. To streamline the user experience and foster community collaboration, the AWS IoT C-SDK began utilizing git submodules for FreeRTOS libraries related to connectivity, security, and AWS IoT services in late 2020. The AWS IoT C-SDK now includes demos leveraging these libraries, compatible with Linux systems that use OpenSSL version >1.1.0.
Collaboratively Raising the Quality Development Bar
The collaboration between resources has resulted in a significant increase in the number of commits to the AWS IoT C-SDK. Customers can utilize submodules as a centralized source to track patches, report issues, or submit pull requests. AWS IoT C-SDK users can also engage with the FreeRTOS Community Forums for support and insights related to the libraries. Furthermore, contributions from partners and customers help elevate quality and enrich features ahead of official releases.
The FreeRTOS libraries integrated within the AWS IoT C-SDK adhere to MISRA compliance and employ automated reasoning techniques to ensure memory safety. The implementation of best practices for MISRA compliance enhances code readability, simplifies debugging and maintenance, and guarantees a level of safety, security, and reliability validated by a third party. Automated reasoning techniques involve constructing models (mathematical proofs) to confirm the absence of critical security issues, such as buffer overflows. These proofs are assessed against the codebase using a software model checker called C Bounded Model Checker (CBMC). By passing these tests, projects utilizing the libraries gain validated assurance of code quality and security across all possible execution paths—not just those covered by existing unit tests.
Increasing Flexibility and Removing Dependencies
In addition to the advantages inherited from the FreeRTOS libraries, the libraries themselves are dependency-free and highly efficient for use in small microcontrollers. All libraries within the AWS IoT C-SDK occupy approximately 53KB of statically allocated memory. You can examine the CMakeLists.txt files used by the CMake build system to link the required dependencies and files prior to compilation. For instance, to initiate the AWS IoT Device Shadow demo, you can review specific lines in the CMakeLists.txt at the project’s root to identify the overall project requirements before exploring those of individual demos.
# User C90.
set( CMAKE_C_STANDARD 90 )
…
# Add platform.
add_subdirectory( platform )
…
The only dependency mentioned here is a flag for CMake to utilize the standard C libraries of C90. The platform folder contains porting files for Linux (POSIX) systems, indicating that the shared libraries do not depend on the FreeRTOS kernel. Each demo specifies the exact libraries it requires. For example, the AWS IoT Device Shadow library demo’s CMakeLists.txt details:
# Demo target.
add_executable(
${DEMO_NAME}
"${DEMO_NAME}.c"
"shadow_demo_helpers.c"
${MQTT_SOURCES}
${MQTT_SERIALIZER_SOURCES}
${BACKOFF_ALGORITHM_SOURCES}
${SHADOW_SOURCES}
${JSON_SOURCES}
)
target_link_libraries(
${DEMO_NAME}
PRIVATE
clock_posix
openssl_posix
)
As indicated in the file’s content, to run the shadow demo, it employs coreMQTT for the MQTT client, the exponential backoff algorithm library for managing connection retries, coreJSON for parsing incoming JSON messages, and the AWS IoT Device Shadow library for managing device shadow state operations. Additionally, it utilizes OpenSSL and the POSIX clock for establishing TLS; otherwise, the demo’s only dependency is the standard C library.
The dependencies for the shadow demo and other demos are solely for the included examples. The libraries themselves do not depend on each other—only on the standard C library. This level of composability allows users to select the libraries they prefer or need. To see this in action, check out this demonstration of the coreMQTT library on YouTube, which is an excellent resource.
Collaborating with Other Open Source Projects
For silicon partners who have been engaged with the FreeRTOS ecosystem for over 15 years, the familiarity with shared libraries, the decoupling of dependencies, and MIT licensing have facilitated the porting of the AWS IoT C-SDK to their hardware platforms or the integration of the software into their tools with minimal effort. For customers, this means that the AWS IoT C-SDK seamlessly fits into their platform development workflows, requiring little modification.
The AWS IoT C-SDK effectively showcases connectivity to AWS IoT Core and performs device-side operations with secure, straightforward, and lightweight libraries. The benefits of embracing increased open source values, collaborating with other leading projects, implementing best practices, removing dependencies, and incorporating third-party validation culminate in software that is secure, feature-rich, and customizable to your needs. The AWS IoT C-SDK delivers these advantages across a wide variety of device types and supports a broad range of connected use cases. By leveraging trustworthy open source software, deploying devices at scale becomes easier, paving the way for billions of connected devices to create experiences we have yet to imagine.
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Chanci Turner
Chanci Turner is the Senior Developer Advocate for AWS IoT, concentrating on edge devices. She also leads the AWS IoT EduKit program, utilizing open source tools to educate today’s developers.