9 packets in a connection interval, but then master waited 61 msec

[jshen]

Hi,

I used one nRF52840 dongle and one DK, and placed one sniffer in between to caputure the packets.

The connection interval was set at 7.5 msec, GAP event length is 6 (which is 7.5 msec), MTU is 23 and data length is 27, SoftDevice s140 7.2.0.

Below sniffer captured, shows

- 9 packets in one connection interval

- the highlighted slave response with MD=1, more data, but master didn't reply, instead it waited 61 msec

I read a few Nordic articles describe the maximum packets per connection interval is 6, but there is 9 in this case. Also why master ignored slave's MD=1 packet, instead waited 61 msec.

Could you help me to understand it?

Also, we are trying to achive highest packet per second, so in theory if we set the MTU small enoough and we use 7.5 msec connection interval, can we achive 6 packets per connection interval and reach 800 packets per second between two devices? 

1000 / 7.5 * 6 = 800 PPS

[Edvin]

Hello,

It looks like your central drops out of the connection for a while (but the devices doesn't disconnect).

What sort of application is your central running? Is there a chance that there are some flash operations that may occupy the central for a while?

You mention that you want a certain number of packets per second. While it is possible, it is usually not the recommended way if you want to increase your throughput.

I can strongly suggest that you look into merging more of your packets, so that you can send longer packets, and thus, send them less frequently.

This way, you can get up to 700kbps or 1.3 Mbps, depending on whether you are using 1MBPS or 2MBPS PHY. 

The reason I mention this is that longer packets will mean a lot less headers compared to the payload.

But is your central doing any flash operations while they are connected?

Best regards,

Edvin