development-real-time-transfer.md

description
Lifecycle: In production

Real Time Transfer (RTT)

RuuviTags are nRF52-based devices. The programming is done over Serial Wire Debug (SWD) interface through nRF52 devkit. The RuuviTag can be interfaced to nRF52-DK either through Ruuvi Devshield or a Tag-Connect cable.

The Real-Time Transfer is Segger's technology for printing UART-like messages from the attached Cortex-M device. Test versions of Ruuvi Firmware print out the logs via RTT which can be useful for example when developing your own applications which communicate over GATT.

Connecting the hardware

First you'll need to connect your PC to nRF52-DK via USB-micro cable, then you'll need to connect the nRF52-DK to Ruuvi via devkit or the Tag-Connect cable. nRF52-DK autodetects an external target and programs it, but if there is an issue with connection you can get errors from the software or program the nRF52 onboard the nRF52-DK. You can cut the power measurement jumper on nRF52-DK to be sure to not accidentally connect to the wrong nRF52.

If you get a Tag-Connect cable, be sure to get the 10-pin connector Cortex-M no-legs version or you'll need to solder the wires to pins on DK as above.

Software connection

You'll need to install Segger software and documentation pack. On Windows you can use JLinkRTTViewer which has a GUI for connecting to device and storing the logs to a file, on Linux and Mac OSX you have to use JLinkExe to connect to the Ruuvi and JLinkRTTClient to view the logs.

JLinkExe has to be started first, commands are

• connect
• Device -> NRF52832_XXAA
• Interface -> s (SWD)
• Speed -> 4000 (kHz)
• Restart program and halt -> r
• Once JLinkRTTViewer is connected, go -> g

JLinkRTTClient will connect automatically to the JLinkExe session, just start JLinkRTTClient and start the firmware program on JLinkExe with g.