ULP wireless: over-the-air software upgrades

Ståle Ytterdal, Nordic Semiconductor -August 13, 2014

Revising an ultra low power (ULP) wireless chip’s software in the field has been difficult. But new technology will make it routine - to developers’ and consumers’ benefit alike.

The idea of in-the-field software updating for ultra low power wireless sensor networks (WSN) is nothing new. As far back as 1978, the Distributed Sensor Networks Workshop, held at Carnegie-Mellon University, Pittsburgh, in the U.S., (considered by many to be the root of published WSN research) identified some key functional requirements for future WSNs. These included the need for dynamic modifications and the need to integrate new software versions into a running system.

Today, updating a product’s software via a wireless link is routine; we’re all familiar with updating apps on our smartphones via the cellular network, or downloading security patches for our portable computers’ operating systems via Wi-Fi. Often, we don’t even know these upgrades are happening; for example, some set-top boxes (STB) automatically update their software while owners sleep. And it’s not just the consumer sector that benefits from this flexibility; industrial engineers routinely upgrade the firmware running on field programmable gate arrays (FPGA) at the heart of process control systems, for example.

Nonetheless, over-the-air updates for WSNs are rarely attempted because it’s tough to do. But that’s about to change due to a newly-introduced generation of tiny, coin cell-powered Bluetooth Smart or ANT+ chips that are able to easily and rapidly upgrade their RF protocol software (“stack”) using their own wireless links.

Download, verify, enjoy
Over-the-air upgrading of compact ULP wireless systems-on-chip (SoC) has previously been challenging for several key technical reasons. First, and perhaps most obvious, is the requirement for a robust and reliable wireless link with interference immunity, good bandwidth and low latency. Second, the device requires a powerful embedded processor to supervise the software upgrade. Third, the SoC requires flash memory to allow the previous software to be rapidly overwritten. (Some commercial ULP wireless chips are supplied with one-time-programmable (OTP) or read-only-memory (ROM) that can’t be erased and rewritten (at least not without major difficulties) eliminating any chance of practical software upgrades in the field.) It helps if there is a decent amount of flash memory too – at least enough so the new software can be fully downloaded and verified before the previous version is deleted.

Fourth, and perhaps most importantly, over-the-air software upgrades are much quicker and simpler if the RF protocol software (for example the Bluetooth Smart- or ANT-stack) and the application program are cleanly separated. That way, either can be upgraded without the risk of corrupting the other code. (Again, many wireless chips on the market interweave the stack and the application code making it impossible to update the device without overwriting the entire software (application and protocol stack) – which is both time-consuming and risky.)

Over-the-air upgrades are of benefit to product developers because new features can be added to existing products and bug fixes can be implemented even when those products are in the hands of consumers.

The technology is already here. Nordic Semiconductor, for example, has recently introduced a new stack (SoftDevice S110 v7.0) that includes an “Over-The-Air Device Firmware Upgrade” (OTA-DFU) feature that supports rapid wireless software upgrades of its nRF51 Series SoCs. (Rapid upgrades save power (extending battery life) and limit the risk of a user attempting to use the product before the revision is complete.) OTA-DFU can even be triggered automatically from the consumer’s Bluetooth Smart Ready smartphone, tablet computer or PC.

But what’s more important than the benefit to engineers of over-the-air upgrades is the benefit to consumers. Users gain from major software upgrades that bring genuine new capabilities to wireless peripheral devices throughout the products’ lives. A good example is the introduction of Bluetooth v4.1, replacing v4.0. Previously, a consumer would have to junk the hardware and buy a new product to take advantage of the enhanced stack. Now a fast and simple over-the-air download of the new software would see them able to reap the benefits of features such as lower power consumption and a more robust wireless connection - without parting with more cash.

This article originally appeared in Nordic Semiconductor’s in-house magazine ULP Wireless Q.

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About the Author

Ståle Ytterdal is director of sales & marketing – Asia for Nordic Semiconductor.


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