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.

[Filya]

Hi

I'm not sure if this is due to when notifications are enabled. After talking with his colleague, he says that he sends a request for notification as soon as the connection is established. In this case, I see the same delay (~ 800 ms) as your example, where I do not even send a request for notification.

I also noticed this feature. I also used Xiaomi Redmi Note 6 Pro phones (with Bluetooth module 5.0) and Huawei P Smart (with Bluetooth module 4.2). The delay in applying Huawei is ~ 800 ms. Delay when using Xiaomi (with Bluetooth module 5.0) - ~ 1400 ms. Since the phone with Bluetooth module 5.0 I only have this model and other models don't have, then perhaps this is an isolated case. But if not, then module 5.0 has even more delay, with the fact that data transfer is faster.

In my project it is very critical that so much time is spent on the connection, since Frequent falling asleep is expected. With such a time there will be a great expenditure of energy. The future device will be battery powered.

Xiaomi Redmi 5+; project: ble_app_cscs; application on Android: nrf Connect.

Xiaomi Redmi Note 6 Pro; project: ble_app_cscs; application on Android: nrf Connect.

[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.

[Simonr]

Thanks!

I still don't see why you do the connection parameter update (CONN_PARAM_UPDATE), as that is what takes time in your screenshots. This is not a connection event. There are no screenshots in this thread that shows how much time the initial connection takes. They are all just parameter updates. If you comment this out of your code, are you able to show me that the actual connection takes 800ms, because on my end this never takes more than 30 ms or so with another device, and approx. 200ms with my phone (iPhone 6), which seems to be as fast as this example gets with a mobile device.

My log in nRFConnect when connecting to another DK:

12:45:44.835	Connecting to device
12:45:44.857	Connected to device CD:3D:F1:F2:0C:E0 //The connection event takes 22ms

Best regards,

Simon

[Filya]

Here I provide my screenshots from nRF Connect.

It turns out that the connection itself took 308 ms (14: 54: 52: 408 - 14: 54: 52: 710). After this, the connection parameters are updated several times in a row. When the announcement of updating connection parameters appears for the first time (14: 54: 53: 047), the characteristics window is not active, reading, recording, etc. is impossible.
After the characteristics have been updated for the second time (14: 54: 53: 482), it is possible to read / write from / to the characteristics.
It turns out that all the time, from the beginning of the connection to the ability to read the characteristics, is 1074 ms (14: 54: 52: 408 - 14: 54: 53: 482).