Just FYI that you can find all the FW blog posts from here. Totally 17 posts have been released so far. That’s a lot of info about nRF52 FW development 
- 0: Introduction
- 1: Sleep
- 2: Debugging
- 3: Led blinking
- 4: Button — Interrupt
- 5: Environmental sensing
- 6: Accelerometer — polling
- 7: Battery measurement — naive approach
- 8: RTC
- 9: BLE broadcasting
- 10: NFC reading
- 11: Scheduler
- 12: Bootloader
- 13: Battery measurement — synchronize to radio
- 14: Accelerometer — interrupt
- 15: Watchdog
- 16: BLE GATT connection
- 17: NFC writing
- ??: New target
- ??: On-line configuring