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Troubleshooting high complexity systems like Zephyr requires more thorough tools. Menuconfig allows users to see the layers of their system and adjust settings without requiring a complete system recompilation.

The troubleshoot loop

Modify, compile, test.

Modify, compile, test.

Modify, compile, test.

Modify, compile, test.

How do we break out of this loop of trying to change different settings in a program, recompiling the entire thing, and then waiting for a build to finish? Sure, there are some tools to modify things if you’re step debugging, such as changing parameters in memory. But you can’t go and allocate new memory after compiling normally. So what happens when you need to change things? You find the #define in the code, change the parameter, and recompile. What a slow process!

Moving up the complexity stack

We move up the “complexity stack” from a bare-metal device to running a Real Time Operating System (RTOS) in order to get access to higher level functions. Not only does this allow us to abstract things like network interfaces and target different types of hardware, but it also allows us to add layers of software that would be untenable when running bare-metal firmware. The downside, of course, is that it’s more complex.

When you’re trying to figure out what is going wrong in a complex system like Zephyr, it can mean chasing problems through many layers of functions and threads. It’s hard to keep track of where things are and what is “in charge” when it comes time to change things.

Enter Menuconfig

Menuconfig is a tool borrowed from Linux development that works in a similar way: a high complexity system that needs some level of organization. Obviously, in full Linux systems, the complexity often will be even higher than in an RTOS. In the video below, Marcin shows how he uses Menuconfig to turn features on and off during debugging, including with the Golioth “hello” example. As recommended in the video, new Zephyr users can also utilize Menuconfig to explore the system and which characteristics are enabled and available.

 

 

Every IoT project needs to provision devices that are going to be available in the field. Leveraging open standards, Golioth cuts down on the required time and hassle for IoT development teams.

Provisioning is a critical step in IoT projects when they go to production. Unfortunately, this process remains a mystery for many engineers due to lack of information about the process. At a high level, provisioning is passing configurations and credentials to an IoT device so it can connect securely to the cloud. Once provisioned, the device can send telemetry, receive commands, or be updated (by OTA DFU) when it’s out in the field. How you provision a device depends a lot on the use case. 

(click the image above to see the full diagram)

Example use cases

First, let’s examine a customer-facing product like a smart light bulb. In this scenario, the first step would be for the user to provide WiFi credentials to connect to the user’s home network. On the platform side, the device would obtain a new set of credentials to connect to the backend services. These credentials would be specific to that particular user and device. Later, the user might decide to clean up the device to sell it, so the ability to remove device configurations and deleting a given set of credentials is important. This is a perfect example for using BLE provisioning like shown in the video below.  The user experience is seamless with any existing mobile app used for controlling the bulb and reporting data back from the end device.

Next, we’ll consider factory-level provisioning. An example device like a cellular asset tracker would be pre-provisioned at the factory before being used by your customer. Later the user will only associate that device with their account, but the credentials to talk to the cloud are already set on the device. This can be done as part of the manufacturing process, probing the device via Serial/UART to get the device hardware ID, provisioning it to the cloud, and sending credentials back to the device via the same transport. We can even have different firmware that will only provision in the factory. The device accepts the initial device configuration and saves the credentials to flash. Subsequent firmware that doesn’t have that initial feature enabled, making sure external parties can’t change or reverse engineer the initial configuration.

There are myriad ways that provisioning can be done. Each instance will depend on the factory environment, the capabilities of the user, and on the end application. The video below is a setup similar to the first example explained above, using a Bluetooth application to read and then program the end device, all while working with the Golioth cloud.

Our demo application

As you can see in the video, we developed an end-to-end sample that shows a practical scenario of provisioning IoT devices with a native mobile app, talking with an IoT device over Bluetooth, and provisioning device/credentials in Golioth Cloud. We leverage different tools for doing so:

  • MCUmgr as the device management subsystem and protocol.
  • Zephyr as the real-time operating system, that implements MCUmgr.
  • Open-source mobile SDK to integrate MCUmgr on an app
  • Golioth’s API and the Device/Credentials Management capabilities. 

The MCUmgr community developed multiple types of transports to interact with devices, a benefit of MCUmgr being an open standard and having a vibrant community. One option is to communicate with the device over serial UART using the `mcumgr` cli or even integrate that into your own set of provisioning tools. Another option is to use a mobile SDK that implements MCUmgr protocols over BLE to talk with devices.

We took the Bluetooth approach and forked Nordic’s MCmgr Example application, adding communication with Golioth APIs to manage devices. Once we discover the name of the device, we assign credentials via the REST API and securely send them over Bluetooth to the end device. The device is running one of Golioth’s samples that accepts dynamic configuration for WiFi and DTLS Pre Shared Keys to talk securely with our cloud. The device uses a different Golioth service called LightDB. Using this configuration engine, we can publish the on/off state of the light bulb using LightDB,show that data on a UI, and even send commands to change the state on the device. 

Source code for the mobile app:

More details on how to use our REST API and how to generate API Keys can be checked on our docs website.

References

A possible solution

Let’s pretend you’re in the middle of a global chip shortage.

Surprise! There’s no need to pretend, as we are all currently in the middle of a global chip shortage. Right now it’s very difficult to source certain components.

“Why don’t hardware makers just switch out the components when they can’t source them during the chip shortage? In fact, why don’t people switch chips on a regular basis?”

As a generalization, switching costs for embedded devices are very high. If we were able to magically solve all of the switching costs for the hardware, you’d still need to deal with the switching costs of firmware and cloud platforms. This often is even more dire than than the hardware switching costs. It’s significant at both an individual level (rewriting firmware to target different architectures and board setups) and at an institutional level (maintaining different platforms and interoperability).

Operating systems and Real Time Operating Systems (RTOS) help by abstracting away a lot of the individual hardware details. When a new device is added to an RTOS, it needs to fit within the constraints of the system. If your board has an i2c sensor on it, you need to ensure your supporting firmware for that board or chipset capable of working with the elements of the RTOS. Then you can take advantage of the drivers already written for other boards/chipsets on the platform. Assuming you are willing to work within that system, you can start to supercharge your development. It’s possible to switch out components quickly and confidently, helping to alleviate the woes of the chip shortage currently underway.

Making the switch

Let’s say you have a board using an ESP32 module. Due to sourcing problems, you can no longer source a particular LED on your board, but you don’t want to change your PCB. Instead, you ask a technician wire in an extra LED to a spare pin you have on your production board that has a larger landing area. You need to build a firmware image to drive a different pin on the microcontroller than you previously were using. Now “LED2” (as it’s called in your program) is not driving pin 18, but is instead driving pin 22. With Zephyr overlays, the switch will take 5 minutes. As Marcin shows in the video below, the device tree overlay is where we map the signals internal to the firmware to the physical pins being used.

Now let’s say you cannot source the ESP32 at all, for some reason. You could create a new overlay file for a different target that works with Zephyr, assign the pins to target the functions you need on a new PCB containing a different chip, and then target that device. The time consuming aspect would be checking all of the functions are performing the same as your previous platform. But once you have decided on a new platform, assigning pins and functions to your new device would occur through overlay files.

How to use Zephyr Overlays

In the video below, we  walk through the location and function of overlays in Zephyr. Marcin explains that customization of firmware images for particular hardware targets can be as simple as a different flag on the command line. In this particular example, we are showing how to change the pins for the ESP32 demo. Previously the ESP32 overlay was shown as part of our our LightDB Sample code (docs), which targeted an ESP32-DevKitC in that video.

About The Zephyr Project

The Zephyr Project is a popular and open source Real Time Operating System (RTOS) that enables complex features and easy connectivity to embedded devices.  The project is focused on vendor participation, long-term support, and in-depth security development life cycles for products.

About Golioth

Golioth helps users to speed up development and increase the chances that pilots will be put into production with a commercial IoT development platform built for scale. We offer standardized interfaces for connecting embedded devices to the cloud and build out software ecosystems that allow your projects to get to market faster. Golioth uses Zephyr as part of the Golioth SDK to bootstrap application examples and show how to utilize the range of networking features Golioth enables via APIs.