get data from gzll devices at almost the same time

[astella]

To the kind Nordic support team,

We are evaluating a scenario where we need a "gzll gzp host" to receive data on two encrypted pipes at almost the same time (we modified a little bit gzp).

Of course, the two devices transmitting (each using one of the two encrypted pipes) are interfering with each others, so that it is possible to only get

data from one device at a time. A theoretical solution could be just switch roles, with the "gzp host" becoming a "gzll device" able to do polling, and devices having data to send becoming

"gzll hosts", a little bit like it is done in BLE (It could have consumption impact for example).

Is there any other theoretical solution that you would suggest based on your experience in gzll? 

Thank you very much for your kindness  

[ovrebekk]

Hi Stella

In this scenario I think the best way is to use an old trick in Gazell where you set up the host with more RF channels than the devices, in such a way that each device only uses a subset of the RF frequencies. 

Then you ensure that the two devices will never transmit at the same time on the same frequency, and since the host needs to service all the channels as defined by the timeslot you will get a consistent data stream from both devices. 

To this with two devices you have to give each device N channels, and the host 2*N channels, like this for example:

Device 1: Channel A and C
Device 2: Channel B and D
Host: Channel, A, B, C and D

You also need to make the timeslot period on the device side twice as large as the timeslot in the host, in order to make the devices synchronize with every other channel from the host. 

The side effect of this is that the maximum bandwidth of each device is reduced by 50%, but the upside is that you get consistent bandwidth for each device, and you don't need to worry about interference between them. 

Best regards
Torbjørn

[astella]

Hi ovrebekk thank you very much for your suggestion. It is a very smart and clever way to deal with it. In our case, as we have been modifying gzp so to use two encrypted pipes, we tested it was sufficient to comment a gzll flush instruction host side. 

[ovrebekk]

Hi Stella

Does that mean you have been able to get it working satisfactorily? 

Best regards
Torbjørn

[astella]

Yes exactly, we have been able to get it working satisfactorily for us. We are using two gzp encrypted pipes to collect host side data sent by two devices transmitting multiple packets at almost the same time;each device using only one of the two different pipes. In our case we just had to get rid of gzll_tx_fifo_flush in gzp_preload_ack: that flush instruction (just in our particular case) seems to be deleting the ACK data which might not be read by the fetch packet of a second device.

[ovrebekk]

Ok, good to hear you found a solution.  

Since the gzp library assumes only one pipe is used for encrypted communication there might be some issues like that. 

Best regards
Torbjørn