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NORDIC SEMICONDUCTOR nRF5340 DK Review by Tim Blythman Nordic Semiconductor is known for its wireless communications products and lowpower devices; you can find their parts in many products. This board is based on the nRF5340 SoC (system on a chip), a dual-core ARM chip that can dedicate one core to wireless communications, leaving the main core free for other applications. W e decided to try out the new nRF5340 DK development board from Nordic Semiconductor since it is a bit different from anything we’ve reviewed previously. The suggested applications for the nRF5340 are: ■ Advanced computer peripherals and I/O devices ■ Health/fitness sensor and monitor devices ■ Wireless payment devices ■ Wireless audio devices, eg, headphones, microphones, true wireless earbuds and speakers with Bluetooth Low Energy (LE) Audio ■ Smart home sensors and controllers ■ Industrial IoT sensors and controllers Interactive entertainment devices Remote controls Gaming controllers Professional lighting Wirelessly connected luminaires You could be using devices daily that include Nordic Semiconductor parts without realising. If you’re using something that relies on Bluetooth LE communication, there’s a reasonable chance it includes a chip from Nordic Semiconductor. They also make products that work with other wireless protocols and bands and are known for their low power consumption. While Nordic Semiconductor has a history going back around 40 years, chips like the nRF5340 are based on ■ ■ ■ ■ ■ a line of parts dating to 2012: the nRF51 series is a low-power wireless SoC incorporating an ARM Cortex M0 microcontroller and a 2.4GHz RF transceiver. The later nRF52 series used an ARM Cortex M4. These chips are even at the core of some Arduino boards, like the Arduino Nano 33 BLE and BLE Sense, which have the nRF52840. The Arduino Primo uses an nRF52832, providing Bluetooth LE and NFC via PCB antennas. The BBC micro:bit V2 uses an nRF52833. Fig.1 shows a very small subset of the boards that can be programmed with the nRF Connect SDK, which we will discuss later. There is also the nRF91 series, The nRF5340 DK is well equipped. The ‘target’ nRF5340 chip and the typical complement of components needed for a minimal implementation is located inside the small white rectangle on the right (near the logo). Nearby is a 64MB flash chip, a detachable NFC antenna (on flex PCB; not shown to scale), a PCB trace antenna and some user LEDs and buttons. There is another nRF5340 for programming and debugging, plus various shorting pads and breakouts, including Arduino-compatible headers. 76 Silicon Chip Australia's electronics magazine siliconchip.com.au which implements LTE (a type of 4G mobile phone technology) and GPS (global positioning system). Naturally, these chips operate on different frequency bands than the nRF5 series parts. The nRF53 family is the latest in the nRF5 series, and the nRF5340 DK is a development board for the nRF5340 chip. So it also implements 2.4GHz communication protocols such as Bluetooth and NFC. We have previously reviewed a Nordic product in the September 2002 issue (“One-chip Transceivers”; siliconchip.au/Article/6738). The chip described in that article was the nRF401, a far simpler transceiver than the nRF5340. The nRF5340 Unlike the earlier single-core parts, the nRF5340 is a single chip containing two distinct ARM Cortex M33 cores. The smaller ‘network’ processor runs at 64MHz and is provisioned with 256kiB of flash memory and 64kiB of RAM. The network processor handles wireless communications and, typically, the wireless protocol stack. That can include Bluetooth LE, Bluetooth 5.3, LE Audio, ZigBee and the Matter standard, which all operate on the 2.4GHz ISM (industrial, scientific and medical) band. The nRF5340 does not offer WiFi (which often uses the 2.4GHz band); to do this requires a companion IC. The ‘application’ processor can run up to 128MHz and has a separate 1MB of flash memory and 512kB of RAM. Security is provided by ARM Fig.1: some of the boards supported by the nRF Connect SDK; several Arduino boards and the BBC micro:bit are included. Even if you don’t have an nRF5340 DK, you might have another board that it can program. TrustZone and CryptoCell-312 with secure storage and bootloader. This processor can also access external programs stored in off-chip flash memory via QSPI, expanding the non-volatile storage. Onboard peripherals include full-speed USB, UART, SPI, TWI (I2C), I2S (for audio data) and a 12-bit, 200 kilosample/second ADC. The application processor also implements NFC. NFC allows devices to communicate, pair and authenticate when in close proximity, typically less than 5cm (this technology is used by “payWave” with credit cards and smartphones). This can allow, for example, a Bluetooth connection to be initiated without requiring a PIN code to be entered. The processor cores communicate via a dedicated IPC (inter-processor communication) peripheral on each Power source switch Debug in core and a shared memory area. The two cores are separate enough that it’s entirely possible to use just one of them. A sample ‘empty firmware’ for the application core hands control of the I/O pins to the network core and places the application core into a low-power mode, allowing the network core to do all the work. This may be suitable for designs that can make do with just the resources available on the network core. It’s also possible to design for just the application core, although that would not allow wireless communication. So it’s a capable chip that would easily outperform many of the other chips that we have used in our projects previously, plus it can handle a range of wireless communication protocols. The nRF5340 DK board The nRF5340 DK is the official development kit from Nordic Semiconductor for the nRF5340. It’s a populated PCB measuring 64mm by 136mm – see Fig.2. The reverse side contains only a 2032 coin cell holder and is otherwise covered with information about the roles of the various shorting pads on the front of the PCB. The nRF5340 chip is in the white rectangle on the right. This area also contains other essential components needed for its operation, such as bypass capacitors and a crystal oscillator. A 64MB QSPI flash memory chip sits just outside this area, as does an SWF connector for making RF measurements and a PCB trace antenna for 2.4GHz communications. The nRF USB connector Debug out User-programmable LEDs Current measurement pins SWF RF port for direct RF measurements nRF5340 SoC SEGGER J-link USB connector 2.4GHz PCB antenna External power source External memory LiPo battery connector User-programmable buttons Power switch Direct power supply switch SEGGER J-link OB programmer/debugger Reset button NFC antenna connector Fig.2: the features and documentation of the nRF5340 DK are pretty good. It contains many more features than most people would use; many can be disconnected by opening a shorting pad on the PCB. siliconchip.com.au Australia's electronics magazine December 2022  77 antenna should also be considered an essential component for RF applications. A second micro-B USB socket connects to the USB pins on the nRF5340, allowing USB applications to be tested. The general purpose I/O (GPIO) pins are broken out to headers and edge connectors, including a set of Arduino R3-compatible headers. This means you can use that you can use common shields and modules for prototyping. There is a connector for an included NFC antenna for NFC testing. Four tactile switches and four LEDs are also provided for user interfacing. The remainder of the kit contains a second nRF5340 chip programmed as a SEGGER J-Link Debugger, which provides a virtual mass storage device so you can program the target nRF5340 via a simple drag-and-drop interface. The Debugger chip also provides USB virtual serial ports for communication with the target nRF5340 using its UART peripherals. As well as USB power, a switch allows the nRF5340 to be powered from the 2032 coin cell or a lithium battery connected to a dedicated connector. The Debugger and target nRF5340 can be independently powered if required. There are shorting pads that can be opened to allow the placement of shunt resistors for current measuring. The back of the board is quite sparse; apart from the 2032 coin cell holder, the PCB silkscreen lists the roles of the various sorting pads. External headers are provided for making measurements across the shunt resistors. Numerous other shorting pads can be used to disconnect features on the nRF5340 DK, to allow the pins to be used for other purposes. A small slide switch is provided near the buttons that control several analog switches. This disconnects the debugger chip so accurate current measurements can be made with just the target nRF5340 chip powered. This is especially important at the low power levels that the nRF5340 DK is capable of. As you can see, the nRF5340 DK is not just a simple breakout board, but a fully-fledged Fig.3: the functional features of the nRF5340 DK. To the right are components that could be part of a standalone design, on the left is the debugging and testing circuitry. 78 Silicon Chip nRF5340 implementation accompanied by programming, debugging and testing features. Such an arrangement should allow developers to get their software well advanced and their hardware prototypes very close to complete before needing to step beyond the nRF5340 DK. The full schematic and Altium Designer PCB files are also available for download, easing the design of custom hardware and helping developers see precisely how the development kit board is configured. Fig.3 shows a block diagram of functional parts on the nRF5340 DK. The user guide at siliconchip.au/link/abgy goes into more detail about the various board features and important details like pin allocations. nRF Connect SDK Such a development board is not of much use without an appropriate SDK (software development kit). The nRF Connect SDK is what Nordic Semiconductor provides for the nRF52, nRF53 and nRF91 series of devices. It can run under Windows, Mac and Linux. It uses Microsoft’s Visual Studio Code as its IDE (integrated development environment). The SDK includes protocol and hardware libraries, samples and demo code. Once a project is set up, a single mouse click can compile code and program it to the chip on the nRF5340 DK. There are a few steps to set the IDE up, but it is all fairly intuitive. A video playlist explains the setup process and then shows how to create a basic application using example code, compile it and run it on the nRF5340 DK. Australia's electronics magazine siliconchip.com.au Fig.4: inside Visual Studio Code, code editing is done in the main window on the right, while the nRF Connect SDK provides actions and resources at the left to work with the nRF5340 DK. Once everything is set up, a single click on the button under the mouse pointer will compile the code and program the selected device. That YouTube playlist can be found at siliconchip.au/link/abgz or search YouTube for “nRF Connect for VS Code tutorials”. There is also a text version at siliconchip.au/link/abh0 There were slight differences in the steps required for the versions shown in the tutorials and the latest versions of the software, but it was easy enough to figure out. There are a few steps using the nRF Connect for Desktop program to install the ‘toolchain’ (compiler and programmer software) and Visual Studio Code. A separate Programmer utility can also be installed, which allowed us to use some sample HEX files that we found mentioned in another tutorial. These and other tools can be installed from nRF Connect for Desktop. On our Windows machine, it came to around 4GB installed, including ~3.5GB for the nRF software and ~0.5GB for the Visual Studio Code IDE. After setting up the first sample project, you’ll see a window much like Fig.4. The code for main.c is in the large window on the right, while the panels give a range of information. Compiling and programming the project takes only a single click on the button under the mouse pointer. The sample software for the siliconchip.com.au nRF5340 chip is based on the Zephyr RTOS (real-time operating system), which has support for different chips, including many based on the ARM architecture. Similar to an operating system on a PC, Zephyr RTOS provides a wide range of interfaces and features uniformly on differing hardware. That makes it easy to get the same software running on various devices. Zephyr is optimised for use on smaller devices such as microcontrollers, and there are many libraries provided that offer simple interfaces to the peripherals. nRF Toolbox app The nRF Toolbox app is available for Android and iOS devices. It’s designed to interface with sample applications (from the nRF Connect SDK) that use Bluetooth LE. So it’s pretty easy to check for Bluetooth functionality. You can download the Heart Rate Monitor demo from siliconchip.au/ link/abh1 It includes a pair of HEX files that can be programmed to the nRF5340 DK using the nRF Connect Programmer tool. This then communicates with the nRF Toolbox app to form an emulated heart rate monitoring device. Fig.5 Australia's electronics magazine Fig.5: the nRF Toolbox app can interface with sample smartphone apps to test features like Bluetooth communication. The suggested uses of the nRF5340 include devices for health monitoring, audio playback/ recording and sensing, all of which would often communicate with a mobile device. December 2022  79 shows the app’s main screen; it’s clear that health and fitness sensors are one of the intended uses of the nRF5340. Testing the sample code We tried a few of the code samples. The nRF Connect add-on in Visual Studio Code makes it easy to clone the examples so we could tinker with the code to see what we could change. There are over 500 examples, including over 100 for different sensor ICs, modules and shields. Not all the examples will work with the nRF5340, but most of the ones we tried did. Complex peripherals such as USB have examples for HID (human interface device, such as mouse and keyboard), CDC (communication device class, for virtual serial ports) and mass storage devices. There are even more diverse examples for Bluetooth and other wireless protocols such as ZigBee. The code is all in the C language. We didn’t have many surprises, and mostly, things worked as expected. There are several NFC examples that work with a separate NFC add-on module and not with the nRF5340’s inbuilt NFC peripheral, so it was simply a case of making sure that we used the correct example. Fig.6 shows an NFC example that worked for us. It emulates an NFC tag that can be read, for example, by an NFC reader app on a mobile phone. The information shown here is displayed in Visual Studio Code, although it is also available on an external browser via the link at the bottom. There are even audio examples available, including Bluetooth audio sources and sinks and USB examples that emulate microphones and headphones. Emulation is necessary because the nRF5340 DK does not have external audio interfaces (although they could be added easily enough). If you are interested in audio applications, there is an nRF5340 Audio DK development kit with an onboard codec chip and a pair of 3.5mm audio jacks for handling real-life audio. In general, we found the trickiest part of creating custom code based on the examples was finding out how to access and control the various peripherals through the Zephyr operating system. One handy aspect of the examples is that they provide liberal debugging data that you can access through one of the virtual serial ports at 115,200 baud. Conclusion The nRF5340-DK has been designed well and is based on the versatile and powerful nRF5340 chip. It is well backed by software that’s easy to set up and use, with many examples. The design files are available, so a compatible hardware design can be developed without hassles. While it is clearly intended to be used to develop standalone products for the nRF5340, it would also be a worthwhile starting point for those who want to experiment with Bluetooth, NFC and other wireless communications. It would be a great way to produce a one-off project, the type that many of our hobbyist readers might consider, especially if it requires Bluetooth or other 2.4GHz wireless communications. The nRF5340-DK can be purchased from these retailers: 1. Mouser (in stock at time of writing): au.mouser.com/ProductDetail/ 949-NRF5340-DK 2. element14 (stock due November): au.element14.com/3617670 3. Digi-Key (in stock currently): www.digikey.com.au/en/products/ detail/NRF5340-DK/13544603 SC Fig.6: NFC allows data to be communicated over short ranges, often to facilitate Bluetooth pairing. In the sample software shown here, the nRF5340 DK is programmed to emulate a tag carrying data that can be scanned by a device with an NFC reader, such as a smartphone. 80 Silicon Chip Australia's electronics magazine siliconchip.com.au