rssi sd_ble_gap_rssi_start sample interval

Question

Hi, 
 I'm using nRF51822 with SD130 (SDK 12.1). 
 I had a firmware based on mbed that had RSSI update, and it was getting quite a few updates per second. 
 I've now gotten rid of mbed, and when using sd_ble_gap_rssi_start(p_ble_evt->evt.gap_evt.conn_handle, 0, 0) when connected but not actively communicating, I receive about 2 updates per second.
As far as I remember, BLE spec says that a device must emit a packet on each channel hopped on, even if having "nothing to say". So I am wondering if there is a way to get RSSI on "empty packets". 
 Thanks for your help!

endnode · Accepted Answer

I would expect that RSSI will be logged for every packet so if your connection interval is way lower then half a second you should be able to get more samples. According to S130 V2.0.1 description from Infocenter there are actually three ways of RSSI reporting during connection: 
 
 Event based which will callback the APP on each connection event (Variant #1). (this is what you are looking for so just make sure you really use interval lower then half a second and that you call the function with right parameter). 
 Event based which will callback the APP only when RSSI changes by given threshold (Variant #2). - if you call sd_ble_gap_rssi_start function with wrong parameter this might be what you see. 
 Polling based approach where you send sd_ble_gap_rssi_get function call each time you expect new sample and from response code you need to see if new value was loaded or not. 
 
 If your first method fails you might try to combine third one with timer (which is close to connection interval timer) and see if values are there and how much they vary }however I would expect first approach to work so this is just to confirm and by preparing some short sampl try to get Nordic support team to investigate bug report).