Hi,

i have a bluetooth device built on BGM121 which sends sensor data to a smart phone. If the smart phone is not connected or loses connection, The sensor data is still gathered and stored in a flash memory attached to the BGM121.

When the smart phone reconnects, the BGM121 sends all missed data from the flash to the smart phone.

So what i need is accurate timestamping of the sensor data.

My idea is that on the first time after power up when the BGM121 connects to the smart phone it gets the correct time from it.

It then keeps its internal date/time using something like this method:

http://community.silabs.com/t5/Bluetooth-Wi-Fi-Knowledge-Base/Using-RTCC-as-Timer-or-Calendar-while-running-BLE-stack/ta-p/180402

When it loses the connection to the smart phone, it uses its internal date/time to timestamp the sensor data samples and then stores it in its flash.

Then when it regains connection it sends all the stored data to the smartphone.

SO:

I wonder about two points here:

1. On first powerup the smartphone (which is BLE client) needs to write the current date/time to the BGM121. Unfortunately the official BLE current time service doesnt support writes, so i think i can never "set the clock right" in my BGM121 using this service. Whats the alternative? Custom service? Or is there a better way to do it?
2. If the smart phone lost connection to the BGM121 and then reconnects to it again, say after 5 hours, will the clocks have drifted significantly? Do i have to resync somehow and what if this makes a "gap" where there is no sensor sample?

I think i need some expert advise to tackle this problem properly, can you please suggest a robust solution?

Thanks a lot,

Sds