Connection Interval

[Filya]

Hi everyone,

I'm new to working with Bluetooth/

My problem is that the connection interval time sent by the central device does not converge with the time I see using an oscilloscope or a configured timer for 1 ms.
The principle of operation of my program is that the peripheral device sleeps for a certain time and wakes up at a specified interval. The central device at this time is trying to connect to it. Using the timer, I count the time from when the device woke up to the time of the BLE_GAP_EVT_CONNECTED event and to the time of the BLE_GAP_EVT_CONN_PARAM_UPDATE event. The time difference between these events is about 600 ms. I can not understand why such a difference in time. Maybe I did not correctly understand the meaning of the parameters MIN_CONN_INTERVAL and MAX_CONN_INTERVAL? If so, then how can you reduce the time for a full connection, so that the BLE_GAP_EVT_CONN_PARAM_UPDATE event occurs as soon as possible.

To check what the actual value is transmitted by the central device, you can make a breakpoint during the execution of the program at the time of the BLE_GAP_EVT_CONN_PARAM_UPDATE event, which I actually did.

According to the received data, the central device set the value of the maximum and minimum interval of 7.5 ms.In the peripheral device, I have the following parameters:

MIN_CONN_INTERVAL    MSEC_TO_UNITS (7.5, UNIT_1_25_MS)

MAX_CONN_INTERVAL   MSEC_TO_UNITS (30, UNIT_1_25_MS)

SLAVE_LATENCY            1

CONN_SUP_TIMEOUT   MSEC_TO_UNITS (250, UNIT_10_MS)

I also read that the connection interval can vary from 7.5 ms to 4 s, maybe this value is the connection interval for my central device?

Chip: BT840F (analog nRF52840);

SDK: nRF5_SDK_15.2.0;

Softdevice: s132_nrf52_6.1.0_softdevice;

Phone: Xiaomi Redmi 5+.

Thanks in advance for your help.

[Simonr]

Hi

I think I have lost track on what exactly you are trying to achieve here. Sorry about this, but could you explain to me once more, where you are in your project now, and what it is exactly you want to achieve. If you have done any changes to your code since the last one you sent me, please attach an updated version of your code as well.

Best regards,

Simon

[Filya]

Hi

The principle of the project, which I do this: on the peripheral side are sensors. The device itself sleeps and wakes up at a certain interval, connects to the central device to transmit the values ​​received from the sensor, and then falls asleep again. The central device is a smartphone (with Android OS).

Since the peripheral device is battery powered, it is necessary to reduce power consumption and time of reception / transmission. When I began to look more closely at the time of connecting and transferring data, I saw the situation that I described earlier.

Since the connection takes from 800 ms to 1300 ms, which was shown earlier, depending on the Bluetooth module (or something else depends on), I need to know whether this time can be reduced or not.

The code changes in the example ble_app_cscs were not. The situation with the time spent on the connection is the same in this example, and in my main project.