Strange Delay - Does sd_ble_gatts_hvx buffer?

Question

//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 · Accepted Answer

@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.

Strange Delay - Does sd_ble_gatts_hvx buffer?

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