Firmware on the MetaSensors is closed source. All MetaSensors are pre-loaded with the MetaFirmware which gives you access to raw sensor data and other commands via SDKs.
Firmware development on the MetaSensors is not recommended or supported by MbientLabs.
If you wish to develop your own firmware, you will need to head over to the Nordic website and follow their recommendations.
If you want MbientLab to develop firmware for you, please send us an email at: hello[at]mbientlab[dot]com.