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]

Hi,

The behavior looks normal to me. The radio on the nRF51 will consume ~10.5mA when in TX mode with 0dB transmit power, and with DC/DC disabled. See the table 36 in Chapter 8.5.2 page 50 in the PS. Then you have the CPU consuming ~ 4.4 mA when it’s not in sleep mode. In total this will give you a peak current around 15 mA. Note that if you enable DC/DC mode, the peak current should drop with ~2.5 mA. (radio will consume 8 mA instead of 10.5 mA). Note that with such a short connection interval as 7.5 ms, the radio will be on more often and the average current consumption will naturally increase.

If you are interested in current consumption on the nRF51, I recommend taking a look at this post.

[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.