Radio Pulses per transmit interval

[josephwinnDJ]

Hi:

We're working with a 3rd party testing agency for our product that is using SDK 11 with S132 Softdevice 2.0.0. 

If I understand correctly, the SDK allows up to 6 transmit packets per connection interval.  Our testing party is capturing 9 radio pulses in their measurement from our device under transmit test.

Are there some overhead or connection management packets that are normally transmitted in addition to the transmit data, or a configuration parameter we're overlooking?  We just need to explain with our testing agency to account for the observed radio activity.

Thanks

Joseph

[ovrebekk]

Hi Joseph

Keep in mind that the receive and transmit will show up as separate pulses. If you see 9 pulses this probably corresponds to the peripheral receiving 4 packets from the central, responding to each of them with it's own packet, and then turning on the receiver for the fifth time without receiving anything from the central. 

The time between packets in Bluetooth should be 150us, which you can probably verify by enlarging the plot in the time axis. 

Best regards
Torbjørn

[josephwinnDJ]

Hi Torbjørn:

As a followup, we measured the VDD current consumption into the micro via a series resistor in attempt to isolate transmit activity from receive.

With our board connect to our app and firmware invoked to stream data to the app, we observe 8? power current pulses.  Considering that in this state we should be saturating the 6 transmit buffers, can you help explain the additional 2 pulses?

Thanks,
Joseph

[ovrebekk]

Hi Joseph

Apparently the 6 packet limit is not an absolute maximum, it is just the maximum that the stack can guarantee. 

If you process the events fast enough on the peripheral side it is possible to start reading out the data during the connection event, which will free up more buffers in the stack immediately. When this happens it is possible to receive more than 6 packets in one connection event. 

Best regards
Torbjørn