Timekeeping on CC2540

Hello,

We're trying to build an application with the CC2540 where the accuracy of the time is very important. We're using the OSAL_ClockBLE.c functions to set and get the time. However, the difference with a reference clock get quite high over the course of 24 hours. In our case we communicate every second over BLE and in 24 hours the CC2540 time was around 10 minutes off. 

Any ideas how we can make this more reliable? We've been testing on the CC2540MINIDK_EM device and a ConnectBlue module with the CC2540 chip on board.

Thanks a lot in advance!

Tijn