This blog post details the author's successful, yet extremely tight, implementation of a full Wi-Fi networking stack (including TLS) on the memory-constrained nRF9160. Using the Zephyr RTOS, they managed to squeeze in lwIP, mbedTLS, and other necessary components, leaving only about 1KB of RAM free. This required careful configuration and optimization, particularly within lwIP, to minimize memory usage without sacrificing essential functionality. The author highlights the challenges of working with the nRF9160's limited resources and shares specific configuration adjustments, such as reducing TCP window size and disabling IPv6, that enabled them to achieve a working Wi-Fi connection. The post serves as a practical demonstration of pushing the boundaries of what's possible on this resource-constrained platform.
Daniel Mangum's blog post, "Just barely fitting a full wi-fi stack on the nRF9160," details his challenging but successful endeavor to implement a complete Wi-Fi station functionality on the memory-constrained nRF9160 System-in-Package (SiP), a device primarily designed for cellular IoT applications. The nRF9160, known for its low power consumption and integrated LTE-M/NB-IoT modem, possesses a relatively limited amount of RAM (256KB) and flash memory (1MB), making the integration of a resource-intensive Wi-Fi stack a significant undertaking.
The author initially attempted to utilize the readily-available lwIP (lightweight IP) stack, a popular choice for embedded systems due to its small footprint. However, even after aggressive configuration optimization, lwIP, coupled with the necessary Wi-Fi driver and related dependencies, exceeded the nRF9160's available RAM. This led to exploring alternative, even smaller TCP/IP stacks.
After considerable research and experimentation, Mangum identified the uIP (micro IP) stack as a viable candidate. uIP, designed specifically for extremely resource-constrained environments, offered a significantly reduced memory footprint compared to lwIP. However, integrating uIP with the nRF9160's Wi-Fi subsystem presented its own set of challenges. The process involved intricate memory management strategies, careful selection and configuration of supporting libraries, and meticulous optimization of the entire software stack.
The author meticulously describes the modifications and configurations required to successfully integrate uIP with the nRF9160, highlighting the various trade-offs made to achieve a functional Wi-Fi station within the limited memory constraints. This included disabling certain features and optimizing buffer sizes to minimize RAM usage.
Ultimately, Mangum managed to fit a complete Wi-Fi station implementation, including the uIP stack, the required drivers, and all necessary supporting libraries, within the nRF9160's restricted memory. The post emphasizes the tightness of the fit, implying that further additions or expansions to the software stack would likely be impossible without exceeding the available resources. The successful implementation, despite the inherent challenges, demonstrates the feasibility of utilizing the nRF9160 for applications requiring both cellular and Wi-Fi connectivity, albeit with careful consideration and optimization of the software stack. The author's work opens up possibilities for using the nRF9160 in scenarios demanding dual connectivity within a single, power-efficient device.
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https://news.ycombinator.com/item?id=43087288
Hacker News users discussed the challenges and ingenuity of fitting a full Wi-Fi stack onto the resource-constrained nRF9161. Several commenters expressed admiration for the author's accomplishment, highlighting the difficulty of working with such limited resources. Some questioned the practical applications, given the nRF9161's integrated cellular modem and the availability of smaller, cheaper Wi-Fi microcontrollers. Others suggested potential uses like captive portals or bridging between cellular and local networks. The Zephyr RTOS was mentioned as a contributing factor to the project's success due to its small footprint. One commenter shared their experience with similar memory constraints on embedded systems and offered debugging advice. The discussion also briefly touched on the implications of this achievement for IoT devices and the potential for further development in low-resource Wi-Fi applications.
The Hacker News post "Just barely fitting a full wi-fi stack on the nRF9151" has generated several comments discussing the challenges and implications of running a Wi-Fi stack on a resource-constrained device like the nRF9160.
One commenter highlights the difficulty of fitting lwIP (a lightweight TCP/IP stack) onto the nRF91, pointing out that even with optimizations, it barely fits within the limited RAM. They express surprise that the author managed to squeeze it in, acknowledging the impressive feat. This comment also mentions that the real challenge lies not just in fitting the stack, but also in ensuring stable and reliable operation given the tight memory constraints.
Another comment chain delves into the intricacies of memory management within embedded systems like the nRF91, specifically discussing the separation of the application processor from the network processor. This separation introduces complexities in memory allocation and communication, influencing the overall performance and stability of the Wi-Fi implementation.
Further discussion revolves around the trade-offs between using the nRF91's built-in LTE modem versus adding Wi-Fi functionality. While the nRF91 is designed primarily for cellular IoT applications, some commenters express the need for Wi-Fi in specific scenarios, either as a backup connectivity option or for local network access. The comments weigh the pros and cons of each approach, considering factors like power consumption, cost, and complexity.
A user questions the choice of not using the ESP32, a popular microcontroller known for its integrated Wi-Fi capabilities. The author responds, clarifying that the nRF91 was chosen for its integrated cellular modem and the project's specific requirement for both cellular and Wi-Fi connectivity in a single device. This exchange emphasizes the importance of selecting the right hardware for the intended application, considering factors beyond just Wi-Fi capability.
Several other comments express general interest in the project and appreciate the author's detailed write-up of their experience. They acknowledge the complexity of working with resource-constrained devices and applaud the author's ingenuity in making it work.