Thomas Embla Bonnerud, Product Management at Nordic Semiconductor explores new wireless SoCs that integrate silicon radios, powerful microprocessors and flash memory together with a novel approach to software architecture
The 2.4GHz ultra low power (ULP) wireless sector has transformed in the last three-to-five years. From being a niche technology back then, proprietary products, ANT chips and Bluetooth low energy devices have pushed wireless connectivity powered by coin cell batteries into the mainstream. And now things are about to explode. It seems very likely that proprietary technology will continue to be successful because such products can be optimised for applications such as wireless desktops where minimal latency and low power consumption are very important.
But technologies such as ANT+ from ANT Wireless and Bluetooth low energy are rapidly expanding because they are able to seamlessly communicate with devices such as smartphones, PCs, and ‘health hubs’ from many manufacturers. That interoperability supports huge new wireless ecosystems.
In response to the booming wireless market, Nordic Semiconductor, has implemented a strategy of three separate product families supporting proprietary technology, ANT+ and Bluetooth low energy (a hallmark element of the latest Bluetooth v4.0 specification) respectively.
This is proving successful but customers are increasingly asking for greater flexibility. They are requesting for capability to design products around one technology and then swap to another with minimal redesign if market conditions dictate. Better still, customers would like to introduce products supporting a new technology – such as Bluetooth low energy – while at the same time retaining the capability to communicate with legacy devices that use a more established RF software protocol.
ULP wireless connectivity technology has not been previously available on the market that meets these demands – until the release of Nordic’s nRF51 Series.
The philosophy behind the new range is to offer OEMs and ODMs common silicon that is equally adept at running proprietary protocols as it is running interoperable software stacks like ANT and Bluetooth low energy.
At the heart of these Systems-on-Chip (SoC) are brand new 2.4GHz radios allied to powerful ARM Cortex-M0 microcontrollers (see figure 1). The ARM microcontroller is a 32-bit device that brings more powerful computing compared to the 8-bit 8051 core typically embedded in ULP wireless SoCs.
The microcontroller has been designed for ULP operation and is well suited to these types of wireless connectivity applications. But while the hardware is impressive, the key innovation is in the application and RF protocol firmware.
In typical ULP wireless connectivity applications the application code and RF protocol exist as part of a singular overall framework. This arrangement puts a lot of pressure on the developer to ensure applications perform as expected and in a timely manner, otherwise, disruptions can cause problems for the RF protocol.
The company’s new products address this challenge by creating a clean separation between the application and protocol stack elements. This effectively removes all dependencies between the two. The stack, which is delivered in its entirety by the silicon vendor, is completely separate from the application in terms of dependencies.
Required resources needed by the stack are guaranteed in terms of availability and in terms of response times. This encapsulation of the stack as a separate entity to the application brings very significant advantages.
In summary, the application developer can build, or port an application safe in the knowledge there are no compile or run-time associated dependencies or potential conflicts.
In addition, this arrangement means the developer can focus on developing in exactly the manner that serves the application best. This is not the case with current wireless connectivity ICs whereby application and protocol code have an associated inherent coupling. Consequently, developers have to be on their guard for constraints and dependencies during the whole development cycle. Debugging can also be very time-consuming and difficult.
From an architecture perspective the nRF51 has two clear functional blocks that have complete autonomy from each other. The first block is the developer’s application, the second is the protocol block which the company calls the ‘Soft Device’. The Soft Device is a self-contained protocol block that has two variants, either a Bluetooth Low Energy stack or an ANT stack.
The memory architecture is designed to be fundamentally ‘thread-safe’ in operation, which ensures application and RF protocol software operate in a secure and predictable manner.
In this arrangement, the Bluetooth low energy RF stack operates separately as a soft device while the protocol works together with the application program (see figure 2). A Soft Device manager decides which protocol takes priority and ensures that the other protocol is disabled. The devices discussed here provide ultra low power consumption and flexibility and are a good platform for the major RF protocols.
Nordic Semiconductor
