RTOS options
Basically, a real-time operating system (RTOS) provides a deterministic task scheduler. Although the scheduling rules change depending on the scheduling algorithm, we know that the task we create will complete in a certain time frame within those rules. The main advantages of using an RTOS are the reduction in complexity and improved software architecture for easier maintenance.
The main real-time operating system supported by ESP-IDF is FreeRTOS. ESP-IDF uses its own version of the Xtensa port of FreeRTOS. The fundamental difference compared with vanilla FreeRTOS is the dual-core support. In ESP-IDF FreeRTOS, you can choose one of two cores to assign a task, or you can let FreeRTOS choose it. Other differences compared with the original FreeRTOS mostly stem from the dual-core support. FreeRTOS is distributed under the MIT license. You can find the ESP-IDF FreeRTOS documentation at this URL: https://docs.espressif.com/projects/esp-idf/en/latest/esp32/api-reference/system/freertos.html
If you want to connect your ESP32 to the Amazon Web Services (AWS) IoT infrastructure, you can do that by using Amazon FreeRTOS as your RTOS choice. ESP32 is in the AWS partner device catalog and is officially supported. Amazon FreeRTOS brings the necessary libraries together to connect to AWS IoT and adds other security-related features, such as TLS, OTA updates, secure communication with HTTPS, WebSocket, and MQTT – pretty much everything needed to develop a secure, connected device. An example of using Amazon FreeRTOS in an ESP32 project is given here: https://freertos.org/quickconnect/index.html
Zephyr is another RTOS option with a permissive free software license, Apache 2.0. Zephyr requires an ESP32 toolchain and ESP-IDF installed on the development machine. Then, you need to configure Zephyr with them. When the configuration is ready, we use the command-line Zephyr tool, west, for building, flash, monitoring, and debugging purposes.
If you are a fan of Apache Software, then NuttX is also an option as an RTOS in your ESP32 projects. As it is valid for other Apache products, standards compliance is a paramount driving factor in the NuttX design. It shows a high degree of compliance with POSIX and ANSI standards; therefore, the APIs provided in NuttX are almost the same as defined in them.
The last RTOS that I want to share here is Mongoose OS. It provides a complete development environment with its web UI tool, mos. It has native integration with several cloud IoT platforms, namely, AWS IoT, Google IoT, Microsoft Azure, and IBM Watson, as well as any other IoT platform that supports MQTT or REST endpoints if you need a custom platform. Mongoose OS comes with two different licenses, one being an Apache 2.0 community edition, and the other an enterprise edition with a commercial license.
Our choice in this book will be FreeRTOS and we will also discuss Amazon FreeRTOS features when we connect to AWS IoT.
