Strange Delay - Does sd_ble_gatts_hvx buffer?

[muhkuhns]

//Edit:

So Hung Bui just told me in another question, that there is indeed a buffer of size 6 or so? How can I decrease that to 1 (i.e. disable it) so that only the latest sd_ble_gatts_hvx is in queue?

Hello,

I am using a setup of 4 peripherals connected to one central (nRF51-DK) to collect measurements..

My code is based on the multilink example. It basically works fine but there is a strange delay of about 7times the connection interval.

The peripherals measure e.g. every second. Then notificate it to the central.

The central prints out all 4 measurements every second.

Connection Interval = Interval for Measurements = Interval for notification = Intervall for printf

If I force change the measurement value, it has ~5seconds delay before it appears on screen. The sensor is more than fast enough.

central - main.c

central - client_handling.c

peripherals - main.c

[Hung Bui]

@Muhkuhns: No you can't change the buffer size. You can monitor the number of packets being sent by checking the count number when in TX_COMPLETE event. However, it would be more simple if you use indication instead of notification. There will be only one indication can be queued at a time. And you can't send another infication before the first one finished.

However, BLE is not real time protocol but a reliable protocol, so a packet will be re-transmitted until it's received and acked by the peer device. So even in the case that you only send one notification/indication at a time you have no guarantee when will the peer device receive it.

I would suggest you to add a timestamp into the notification/indication packet. So that the master when receive the packet can find when the data is sampled regardless when it's actually received.

[Hung Bui]

TX completed only tells about the number of packets it sent in the last connection event. If you only have one characteristic that notify, the sum of count number on each TX completed should tell exactly the number of packet you sent.