BLE Mesh Time Synchronization

[meshs]

My goal is to synchronize the clocks of several nodes in a mesh network. I would like the client node to distribute the current time to all the server nodes in the network. Would broadcasting a time-stamp from the client be a solution? The client should afterwards expect an acknowledge from all servers within a given time-frame. I realize this will probably be a very poor form of synchronization, but I don't know exactly how awful it is.

Is there any functionality for this purpose in the 0.10-alpha SDK or elsewhere? I would assume something performing the synchronization at a lower layer in the stack.

[ketil]

Hi,

We do not have a global clock implemented but it is on the roadmap.

You can implement the time synchronization the way you suggest. Be aware that the clock will drift and you should set a new global time with some regular interval depending on the desired accuracy. The drift of the 32MHz crystal is typically 20ppm.

We recommend that you only broadcast your time to the closest neighbours as relaying the time can lead to lost accuracy.

Ketil

[Henry]

Is there any update on the issue?
Also, I want to ask whether it is possible to sync time with error < 1ms with BLE.

[bjorn-spockeli]

Henry: There appears to be a misunderstanding related to this global clock feature, I can at least not find it in any roadmap. Hence,I doubt that this feature was in the roadmap at all and this is not a feature we currently plan on implementing. As for your question if it is possible to synchronize devices within 1ms, the answer is yes. Please take a look at this blog post. 

Best regards

Bjørn 

[kenjiume]

Hi,

I read that blog post  and confirmed that the sample project in github(nRF5-ble-timesync-demo) worked fine with two nRF52DK boards. After that, I merged the project with the light switch example in mesh SDK(v2.2.0). 

Unfortunately,  nrf_stack_init() calls timeslot_start() function and  sd_radio_session_open() in it returns NRF_ERROR_BUSY. (called the same function in ts_enable() in time_sync.c before)

So, Is it possible to coexist meshSDK with the time synch functionality written in the blog post?

Regards,

Kenji

[bjorn-spockeli]

Hi Kenji, 

both the nRF SDK for Bluetooth Mesh and the Time Sync functionality uses the SoftDevice Timeslot API, so it should be possible to add the Time Sync functionality to Bluetooth Mesh devices. However, we do not have any examples covering this and we have not verified it. 

Best regards

Bjørn