Supervision timeout Multiplier - Connection supervisory timeout

[Marc]

Hi,

I made an experiment and the result doesn't correspond with my view on how the BLE communication "connection" mechanism works.

I have an app running on the nRF52832 using example code and here is what I use as a supervisor timeout delay of 4 seconds:

#define CONN_SUP_TIMEOUT                 MSEC_TO_UNITS(4000, UNIT_10_MS)             /**< Connection supervisory timeout (4 seconds). */

...

memset(&gap_conn_params, 0, sizeof(gap_conn_params));

gap_conn_params.min_conn_interval = MIN_CONN_INTERVAL;
gap_conn_params.max_conn_interval = MAX_CONN_INTERVAL;
gap_conn_params.slave_latency     = SLAVE_LATENCY;
gap_conn_params.conn_sup_timeout  = CONN_SUP_TIMEOUT;

err_code = sd_ble_gap_ppcp_set(&gap_conn_params);
APP_ERROR_CHECK(err_code);

I have a Faraday cage, grounded, www.everythingrf.com/.../718-645-tc-5921ae

With this box, I put the nordic device in it and I can cut the communication by closing the box. Using a USB Serial that pass thru the box, I can monitor device events such as disconnection.

Using a computer Bluetooth dongle I initiated the BLE connection, close the box and measure the time I see the disconnect message in the log. We did this to check the device reliability and as expected, the device disconnect after 4 seconds. This was repeated a lot.

I repeated the experiment but this time with an Android device, Alcatel One touch Idol 3, with the nRF Connect app. With this setup, the delay before disconnection is around 20 seconds!

My understanding of 'conn_sup_timeout' is the delay of no activity (no "connection packet" received) before assuming the connection lost and disconnect.

How the central device, Android or PC, could affect or change this interval?

Thanks

[endnode]

No, there is nothing wrong on your side and not much you can do, this is world of hundred thousand Android devices with embedded BT (+BLE) stacks written by people who don't care much about the specifications. I've seen different time-outs on different Android 4.4-6.0 devices, things between 1 and 20 seconds regardless Supervision timeout value set in Connection Request parameters. In the end I just swore to my cup of tea and accepted it as fact. Welcome to the business!:)

[endnode]

Interesting question. Not having sniffer you have only event trace from nRF FW's SD event handle on Nordic so firstly log everything over UART or RTT. Also using Nordic sniffer on $40 nRF51 DK might give you some more data with little bit of patience (it's nice tool but cannot compete with several thousand USD devices from Frontline or similar companies so you need to do more re-tries to catch all necessary packets).