Bluetooth connection context

RE: Bluetooth connection context

novello — Wed, 09 Nov 2022 11:49:55 GMT

oK Thank for the documentation, ... I need some time to study

I will activate the sniffer using 1 Central UART 2 periferal_uart and a sniffer.

Thank also for the examples I have fount (uart_througput).

RE: Bluetooth connection context

Hung Bui — Wed, 09 Nov 2022 10:15:47 GMT

Hi Novello,

Which error do you have ?

I think the most important thing is that you can control the connection interval.

Have you checked which exact connection interval you have on the connection ?

I have made a blog about optimizing connection interval here. Please have a look.

Please try to capture a sniffer trace. From that we can do further analysis of the communication. Made sure you follow an advertiser before you make the connection. The sniffer can only track one connection at a time.

RE: Bluetooth connection context

novello — Wed, 09 Nov 2022 08:05:04 GMT

I Have see the webminar. The main problem is that in the BLE library there are many parameter that are not clear for me.

my multi_nus and the 4 peripheral_uart work well if I send (20byte message every 0.5 second.) If I have to send a message from the central_unit to the 4 peripheral every 80ms I have some errore.

So I'm Trying to modify some parameter to ingrease the throughput but for me is impossible to understand what are:

CONFIG_BT_ACL_RX_SIZE=502 ? (see througput examples)

CONFIG_BT_:AT_PREPARE_CONT=2

CONFIG_BT_L2CAP_TX_BUF_COUNT =10 .. etc.

And how the modify the perfomance of my system. After that I have to setup coded_phy LINK.

RE: Bluetooth connection context

Hung Bui — Tue, 08 Nov 2022 15:29:51 GMT

Hi Novello,

I think you are having a misunderstanding on the Bluetooth connection.

The Bluetooth connection is always ON regardless of the connection interval. It only terminated if you either do a disconnection, or the devices are not in range.

The max and min connection interval doesn't mean it's the connection time. It's the interval. I would suggest to have a look at this video.

For example a connection interval of 100ms meaning that every 100ms the central will ping the peripheral and the peripheral will response to the ping of the central. This way the 2 devices know that they still can communicate to each other.

The super vision timeout is used when the device can't communicate between each other (no ping) for a long time. If the time that they are not communicated is over the super vision timeout the connection will be terminated.

The minimum and maximum connection interval is only the preferable value that the peripheral gives the central, so the central can choose a connection interval inside the range between minimum and maximum connection interval.

RE: Bluetooth connection context

novello — Tue, 08 Nov 2022 15:05:55 GMT

I'm trying to use the Bluetooth connection contex us is used in multi-nus. (for the moment). I need frome a central_uart to connect with 4 peripleral_uart and then send a mesage to the 4 peripheral every 20ms ( I will do the complete loop in 80ms)

If I setup:

peripheral prefered maximun connection interval =65000

peripheral prefered minimun connection interval =65000

Then the connection bettwen the 5 ble devices is always ON.

And I will use the :The unit of super vision timeout is 10ms. So if you set the timeout to value 200 , for example, then it's 200x10ms= 2 seconds. To verify if a device is "dead " There is a callback that inform the application layer that a device is not "visible"?

RE: Bluetooth connection context

Hung Bui — Tue, 08 Nov 2022 14:34:03 GMT

Hi Novello,

[quote user="novello"]

peripheral prefered maximun connection interval for me 20mS (at step of 1.25ms) or it have to be 500mS the connection will be always active. 500mS/1.125ms the maximunh is 65000 .....I CAN USE THIS to be always connected

peripheral prefered latency in connection latency in connection interval ==>0

peripheral prefered supervision timeout in 10mS for me is 100 ==> 1 sec.... Which is the best choise?

[/quote]

Please try to elaborate a bit more clear I don't fully understand what you are trying to describe here.

Note that the minimum and maximum connection interval is only for preference. There is only one actual connection interval used.

The unit of connection interval is in 1.25ms . So if you set minimum connection interval value to 6 it means 6x1.25 = 7.5ms

The unit of super vision timeout is 10ms. So if you set the timeout to value 200 , for example, then it's 200x10ms= 2 seconds.

Please note that the connection interval is not the same as the time it take to establish a connection. The connection interval the interval period when the central "ping" the peripheral.

RE: Bluetooth connection context

novello — Tue, 08 Nov 2022 14:17:36 GMT

The problem is that in 20ms I have also to send 30 byte to the first peripheral,30byte to the sencond peripheral etc. ... to 4th peripheral. Sorry for me is not clear the meaning of:

peripheral prefered minimum connection interval for me is 7ms (at step of 1.25ms) It wil be used the minimun range is 6

peripheral prefered latency in connection latency in connection interval ==>0

peripheral prefered supervision timeout in 10mS for me is 100 ==> 1 sec.... Which is the best choise?

But at the polling rate you have which is 60ms, it's better to keep them all connected I think.!!! So this is the best solution to have the peripheral always connected !

RE: Bluetooth connection context

Hung Bui — Tue, 08 Nov 2022 12:15:35 GMT

Hi Novello,

I don't see any problem using Bluetooth Connection Context here. Please be aware that Bluetooth Connection Context has nothing to do with the connection parameters (connection interval). The main purpose of Bluetooth Connection Context is to store the CCCD values on each connection so that it can restore them when the same central/peripheral reconnected.

You can choose to keep the connection with all of the device simultaneously or you can choose to only connect to one at a time. But at the polling rate you have which is 60ms, it's better to keep them all connected I think.

[quote user=""]I know that a connection will take 7.5mS more or less[/quote]

I assume you meant "connection interval" of 7.5ms ?

If you want to have support for multiple peripherals and if you don't need too low connection interval (7.5ms) I would suggest to use 20ms connection interval. It will be easier for the scheduler to handle multiple connection with slightly larger connection interval (e.g 20ms) .