Things to Consider When Specifying a Wi-Fi Compatible MCU
There are several factors to consider before specifying a particular Wi-Fi MCU. Before making a choice, it is important to understand the different options.
As industrial IoT evolves, we are seeing a greater preference for a single SoC that performs more functions, rather than using multiple discrete devices. This is because a single SoC offers multiple benefits, including a smaller BOM, less design risk, and a smaller footprint. Take the example of a Wi-Fi MCU. It supports a wide range of applications by integrating Wi-Fi connectivity with a processor and GPIO. There are several factors to consider before specifying a particular Wi-Fi MCU. Before making a choice, it is important to understand the different options.
While there are low cost Wi-Fi connectivity options available in the market, they often compromise the number of devices they offer. This makes the choice difficult because robust Wi-Fi connectivity and high performance MCU features are both essential parameters and influence the design speed of the project as well as its efficiency.
Since the MCU is the heart of the Wi-Fi MCU, it is important to focus on the right choice at the start of the project to avoid unnecessary rework when it comes to redesigning the software and changing the configuration midway through. path.
The role of analog-to-digital conversion (ADC)
Although this is the first processing component in the signal chain after analog input, most people tend to overlook the importance of analog-to-digital conversion when specifying a Wi-Fi microcontroller. Fi. Since its performance influences the operation of the entire system, it is essential to understand the key metrics of ADC.
While designers often focus on the bit count of the ADC, the effective The number of bits (ENOB) available for converting is a more important metric. Indeed, in practice, the real number of bits is lower than the specification of the data sheet, sometimes significantly. The closer the correspondence between the ENOB specifications and the datasheet, the better. Fewer bits available for conversion results in less precision in how the SoC represents the input signal.
In addition, like all electronic devices, ADCs can contribute to errors resulting from quantization and synchronization, as well as variations in offset, gain and linearity. ADCs are also notoriously sensitive to temperature variations, which are common in industrial IoT operating environments (see Figure 1). Collecting details around ENOB, temperature, linearity, and accuracy performance from Wi-Fi microcontroller manufacturers, if possible, is an important step.
Figure 1. Low-quality ADCs have poor accuracy and linearity, and are sensitive to the environment and temperature.
Often times, the number of interface standards supported by a Wi-Fi MCU can be insufficient, especially when engineers try to use a Wi-Fi MCU of different designs.
This problem is more pronounced in the case of IoT systems because they involve a wide range of machines and controllers built at different times by various manufacturers. This problem may worsen as the system grows and new interfaces are added.
If the SoC has a GPIO to spare, it is possible to add more relays, switches, and other components that can be controlled with little to no pin sharing. To ensure that virtually all scenarios can be supported now and for the foreseeable future, it is recommended that the device is equipped with supported interfaces such as Ethernet MAC, USB, CAN, CAN-FD, SPI, I2C, SQI, UART, and JTAG (and potentially support for touch sending and display).
Safety starts inside
While security is essential for every IoT application, it is doubly critical in industrial scenarios. Indeed, any threat that enters an industrial IoT network can potentially cross an entire installation and even an entire company. Therefore, it is absolutely crucial to ensure that the first level of security required is in the MCU’s built-in encryption engine. Here, encryption and authentication can be done either sequentially or in parallel. AES encryption in ciphers can have key sizes up to 256 bits, DES and TDES. Authentication must include SHA-1 and SHA-256 and MD-5.
One of the most difficult tasks for designers is to provision their product for a cloud service. Indeed, each cloud service provider has its own certification and its own keys. Provisioning them requires considerable knowledge of cryptography. Fortunately, manufacturers such as Microchip Technology can help simplify this process, saving huge amounts of time and money. This helps meet security and supply requirements with a proven and verifiable approach and with minimal confusion, while saving weeks or more of the design process.
Most Wi-Fi microcontrollers store credentials in flash memory where the data is accessible and vulnerable to software and physical attacks. Storing this information in a hard-coded security element ensures maximum security, as the data it contains cannot be read from any external software. A good example is Microchip’s WFI32 Wi-Fi MCU (Figure 2), which uses this approach in the company’s Trust & GO platform. It enables secure provisioning of its MCUs to connect to third-party AWS IoT, Google Cloud, Microsoft Azure, and TLS networks.
Figure 2. The WFI32 Wi-Fi module isolates credentials by storing them in hardware, making them virtually invulnerable to hackers.
In preconfigured, preconfigured, or custom secure elements, credentials are generated inside the device’s Secure Hardware Modules (HSMs) during manufacture, thus isolating them from exposure during and after production. The Trust & Go platform can be used with an inexpensive Microchip development kit that provides designers with a design suite with tutorials and sample code to create the required manifest file. The design can be sent to production once the C code of the secure element in the application is confirmed to work.
Another security consideration is the latest Wi-Fi security certified by the Wi-Fi Alliance. In the latest version, WPA3 which builds on its predecessor WPA2, there are additional features that simplify Wi-Fi security, enable more robust authentication, provide increased cryptographic strength, and maintain network resiliency. All new devices must be WPA3 certified in order to use the Wi-Fi Alliance logo. Therefore, each Wi-Fi chip and Wi-Fi MCU should be certified for maximum security. So, making sure your candidate Wi-Fi MCU is WPA3 certified is an important step.
Factors such as RF or software incompatibility can hamper a Wi-Fi MCU’s ability to communicate with certain access points in the market. Failure to connect to common access points could damage a company’s reputation. While ensuring the interoperability of a Wi-Fi MCU with all access points (APs) on the planet is virtually impossible, interoperability testing with the most popular APs on the market is important. Obtaining information either from manufacturers’ websites or by requesting it explicitly is an important part of the decision-making process.
You will need help
Supporting design as a full integrated development environment (IDE) platform is the final piece of the puzzle. Ideally, manufacturers should provide a full IDE figure 3 which lists all analog and digital functions performed by the Wi-Fi MCU as well as the role of external components in implementations for specific applications. In addition, it should include means to visualize the impact of design changes on overall performance and the ability to assess design RF performance as well as regulatory compliance.
Without it, designers have to improvise with sub-optimal resources based on online research. For example, some Wi-Fi microcontroller manufacturers stop at providing basic product details and instructions for prototyping rather than providing the information needed to get from that stage to production. While some basic tools are free, others, such as evaluation boards designed to serve the manufacturer’s family of Wi-Fi microcontrollers, are available at a modest cost.
Figure 3. Integrated development like this reduces risk by providing the designer with debugging and other tools from the prototype stage to the finished product.
As the proliferation of IoT devices shifts more processing power to the edge rather than being limited to cloud-based data centers, the ability to integrate more functions in less space and components. becomes important. The Wi-Fi MCU plays an important role in this functionality, as it integrates multiple functions into a single device, thus eliminating the need for discrete, function-specific components.
Integrating these devices into an integrated IoT subsystem can be quite straightforward; although subject to the availability of adequate resources such as a high level of security. In addition, a simple means of provisioning based on specifications from cloud service providers as well as a full IDE that takes the designer from prototype to production are important.
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