Some nRF chips in a small form factor need to be flashed manually. Either by using a J-Link (which can be expensive) or a cheaper ST-Link in combination with openocd.

Steps

1. Install openOCD

2. Connect the pins to the correct ST-Link pins. A sample schematic of an nRF52 Beacon can be found below

3. Build your firmware with the correct keys

4. Run openocd with the correct configuration

   openocd -f share/openocd/scripts/interface/stlink.cfg -f share/openocd/scripts/target/nrf52.cfg
   

   The first parameter here uses the configuration file for the connected interface (stlink-v2) and the second parameter loads the config file for the nrf52 boards

5. Now openocd is running. You can connect to it using telnet:

   telnet localhost 4444
   

   You can get all available commands using the help command

6. Stop the execution with halt

7. You can backup the existing firmware:

   dump_image /Your/File/Path/flash.bin 0 0x40000`
   

8. Erase the flash using

    nrf5 mass_erase
   

9. Verify and program your device by using (use the .bin not .hex file)

   program /your/path/to/the/firmware.bin verify
   program /your/path/to/the/firmware.bin
   

10. Resume the execution

resume

This tutorial is largely based on comment of @sthorley here