Peripheral connection event gives unusual measurement peaks?

[Mathias]

Hi all!

I'm doing some tests on throughput and power consumption on the nRF51822, using SoftDevice 130. I use an application that sends 20 bytes notifications from slave to master on a connection interval of 7.5 ms. I already measured the throughput and get fine results (127, something kbps) when there is practically no interference. Now I'm trying to measure the power consumption on the slave, during the sending of those notifications. After some fiddling and reading, I could make a screenshot like this one:

What worries me is:

• The peaks are quite high?
• I don't really get perfect resemblance to the theory in the SoftDevice 130 specs (infocenter.nordicsemi.com/index.jsp. Especially (A), (B) and (C) are pretty weird (or maybe aren't there at all)?
• The event seems to take pretty long?

Is this still pretty normal behavior? Or is there a serious fault looming?

Thanks!

Mathias

[Sigurd]

Why do you think you messed up the firmware on the dongle ? What code are you running on the dongle? Also, what SDK version are you using?

[Mathias]

I honestly don't know what could have messed it up.. I'm using firmware that nRFConnect for Desktop automatically wants to install when I try to connect to the COM port that the Dongle is using. I'm using SDK 11 on my DK.

What I also tried today is connecting an IPhone 7 as a central with the DK and with that I seem to get 8 packets per interval, which could be possible because the IPhone 7 uses a fairly new BLE chip but the DK uses SoftDevice 130 which supports max. 6 packets per interval so I don't know 8 packets per interval could be possible in this connection...

[Mathias]

After looking into the specs of the SoftDevice 130 I saw that 7 packets per interval could also be possible (giving a max of 149.2 kbps) when communication is just only the peripheral sending notifications to the central and nothing more (simplex communication). But so I don't understand how the DK with s130 allows the 8 packets per interval that the IPhone 7 supports...

[Mathias]

Okay I think that the IPhone 7 doesn't exacly give a higher throughput because I get 8 packets per interval but it seems that the minimum connection interval that the IPhone 7 supports is around 30 ms so the throughput then seems to be ((1/ 30 ms) * 1000) * 8 packets * 20 bytes * 8 = 42.67 kbps, which is much less then the maximum throughput (149.2 kbps). So I'm a bit more at ease now I think. Still don't understand why S130 allows 8 packets per interval though...

[Sigurd]

If you are in fact sending 8 packets per interval, then I guess this is because the increased connection interval (from 7.5 ms to 30 ms) makes it possible to fit the extra packet in the event for the S130. Notice this sentence in the BLE data throughput chapter in the spec:

The SoftDevice may transfer more packets than reserved by the bandwidth configuration when data transfer is simplex (read or write only), because extra time is available in the event to transfer data.