BLE Master-Slave mode can avoid colision?

RE: BLE Master-Slave mode can avoid colision?

Karl Ylvisaker — Fri, 18 Mar 2022 10:10:49 GMT

Hello again,

Thank you for your patience with this.

[quote user="zhangkui"]I don't know the reason why nordic say there the centrle and the peripheral are scheduled indepently. Can you tell me?[/quote]

This is because it is the central that determines the connection parameters entirely, which means that in the peripheral role the device will have no say in what connection parameters will be used - it can only request to have them updated to its own preferences, which the central device may decline.
So in the multirole setting the SoftDevice is able to neatly schedule multiple central roles, but whenever it enters into a peripheral role it will have to follow the direction of the central in the connection.
The priority of the different events will then follow the table from the scheduling documentation you reference above, to make sure that the connection run as smooth as possible.

[quote user="zhangkui"]And I want to know If there is a collision, Will the SDK adjust the timeslot by send connect paramter request message to the centrle or send connect update request to the peripheral?[/quote]

If there is a collision then the SoftDevice will follow the priorities listed in the documentation - it will not send connection update requests on its own, so if you would like for this to happen you must implement it into your application yourself. I would suggest that you then move the central timeslot that is colliding, since the central is the one that decides (so you do not need to rely on the other central to resolve your collisions).

For more information you could also see the answer by my colleague Einar here.

Best regards,
Karl

RE: BLE Master-Slave mode can avoid colision?

zhangkui — Mon, 07 Mar 2022 06:46:41 GMT

In the SoftDevice scheduling documentation, It said the centle and peripheral roles are scheduled indepently. I have underline it with red line in the pic below.

so we think it hub have centle and peripheral roles. there will be collsion.

But If the hub as peripheral role send connect paramter request message with ReferenceConnEventCount and offset0--offset5 , the peripheral role also can schedule the timeslot .and anchor point.

I don't know the reason why nordic say there the centrle and the peripheral are scheduled indepently. Can you tell me?

And I want to know If there is a collision, Will the SDK adjust the timeslot by send connect paramter request message to the centrle or send connect update request to the peripheral?

RE: BLE Master-Slave mode can avoid colision?

zhangkui — Fri, 04 Mar 2022 14:11:16 GMT

Maybe I describe inaccurate. The center set anchor point only through connect Ind and connect update request.

If a hub have connected a peripheral. There is two case:

1. A new peripheral connect the hub. Will the hub ajust anchor point of the new connection by sending connect ind to the new peripheral?

2. A new center connect the hub. Will the hub ajust anchor point of the old connection by sending connect update request to the old peripheral?

RE: BLE Master-Slave mode can avoid colision?

Karl Ylvisaker — Fri, 04 Mar 2022 13:41:28 GMT

[quote user="zhangkui"]Can you tell me the detail scheduling logic that center SDK excute?[/quote]

What do you mean when you say center SDK?
If you would like to know more detailed information about the timeslot scheduling please see the SoftDevice scheduling documentation I linked earlier.

[quote user="zhangkui"]And the schedule can only be excuted when connecting or connection parameter update?[/quote]

No, the scheduling happens every time a new timeslot or role is added or removed to the list, but the central will have to use connection parameters that fits into the timeslot that the central role has available.

Best regards,
Karl

RE: BLE Master-Slave mode can avoid colision?

zhangkui — Fri, 04 Mar 2022 12:18:54 GMT

And the schedule can only be excuted when connecting or connection parameter update?

RE: BLE Master-Slave mode can avoid colision?

zhangkui — Fri, 04 Mar 2022 12:13:51 GMT

Can you tell me the detail scheduling logic that center SDK excute?

We have different dropping data when the hub be center only or be center-peripheral.

So when the hub be a peripheral to connect a center . Maybe the schedule is not as good as be center only.

RE: BLE Master-Slave mode can avoid colision?

Karl Ylvisaker — Fri, 04 Mar 2022 11:55:57 GMT

[quote user="zhangkui"]If the MIN and MAX interval are different values, when a new BLE is connected, Will the SDK of master change the interval and rearrange the anchor point?[/quote]

The central is the one that decides which connection parameters that will actually be used - the peripheral can only set some preferences, but the central may choose to ignore the peripheral's preferences. The SoftDevice will perform scheduling so that the different timeslots for the different roles do not overlap as according to the documentation, correct.

Best regards,
Karl

RE: BLE Master-Slave mode can avoid colision?

zhangkui — Fri, 04 Mar 2022 10:32:53 GMT

I want to know whether the same MIN and MAX interval will stop the SDK updata connect parameter? If the MIN and MAX interval are different values, when a new BLE is connected, Will the SDK of master change the interval and rearrange the anchor point?

RE: BLE Master-Slave mode can avoid colision?

Karl Ylvisaker — Fri, 04 Mar 2022 10:22:13 GMT

[quote user="zhangkui"]-------you think the buffer for example the quene exceed may drop data before BLE tansmit? But when the HUB be only center, there will no data be dropped.[/quote]

I think this could be the case, yes. Does your call to queue data for transfer ever return with a non-NRF_SUCCESS error code?

[quote user="zhangkui"]-------The MTU is 64, The MIN and MAX interval is 6(7.5ms). If the anchor point of different connection is the key, The connection update ind will ajust anchor point. Which case will the link layer send connection update ind?[/quote]

Connection update indications are sent when one of the devices wants to update the connection parameters / configuration.
Some of these are set by the SoftDevice directly, or you may also request to have the connection parameters updated using the SoftDevice API in your application.

Best regards,
Karl

RE: BLE Master-Slave mode can avoid colision?

zhangkui — Fri, 04 Mar 2022 07:22:06 GMT

n case of the former it sounds like an issue strictly about throughput, in case of the latter we will also need to look into how your application is handling the data up until transmission.

-------you think the buffer for example the quene exceed may drop data before BLE tansmit? But when the HUB be only center, there will no data be dropped.

Which MTU size are you using in your application? If you are operating in an environment with a lot of noise where packets frequently gets corrupted it will help to divide the transfers into multiple packets instead, to reduce the chance of corruption due to noise.

-------The MTU is 64, The MIN and MAX interval is 6(7.5ms). If the anchor point of different connection is the key, The connection update ind will ajust anchor point. Which case will the link layer send connection update ind?

RE: BLE Master-Slave mode can avoid colision?

Karl Ylvisaker — Fri, 25 Feb 2022 08:50:07 GMT

[quote user="zhangkui"]30kbps is also a very low throughput.[/quote]

Yes, 30 kbps is also a very low throughput indeed.

[quote user="zhangkui"]We transmit a wave for example the ECG wave data.. we can see gaps of the wave.[/quote]

Does these gaps indicate that no data was received in time for it to be rendered? Or does it indicate that certain timestamps / parts of the sequence was never received?

In case of the former it sounds like an issue strictly about throughput, in case of the latter we will also need to look into how your application is handling the data up until transmission.

[quote user="zhangkui"]But the noise is big and the RSSI is -75 dim.[/quote]

RE: BLE Master-Slave mode can avoid colision?

zhangkui — Thu, 24 Feb 2022 12:43:17 GMT

We transmit a wave for example the ECG wave data.. we can see gaps of the wave. 30kbps is also a very low throughput. But the noise is big and the RSSI is -75 dim.

We test a multirole connect two slave. The data flow is slave-->multirole-->slave They can achieve 30kbps. No wave gap. And the RSSI is also -75dim.

RE: BLE Master-Slave mode can avoid colision?

Karl Ylvisaker — Thu, 24 Feb 2022 11:53:05 GMT

[quote user="zhangkui"]

All three device set connect interval 7.5ms and event length 7.5ms.

The data flow is slave device-->multirole device-->master device.

The data throughput is 15kbps

[/quote]

Thank you for confirming.
What throughput did you achieve on the central and two peripheral test, for comparison?

Could you elaborate on why you need to have the multirole-intermidiate device, by the way?

[quote user="zhangkui"]If data throughput is 30kbps , it will drop data.[/quote]

Could you elaborate on what you mean when you say that data is dropped? No data is lost on the BLE link, so this must be happening in the application logic.
For the record, 15 kbps is considered a very low throughput, so I suspect that there is an issue with the application somewhere.

Best regards,
Karl

RE: BLE Master-Slave mode can avoid colision?

zhangkui — Thu, 24 Feb 2022 11:29:37 GMT

All three device set connect interval 7.5ms and event length 7.5ms.

The data flow is slave device-->multirole device-->master device.

The data throughput is 15kbps

RSSI is about -75dbm.

If data throughput is 30kbps , it will drop data.

RE: BLE Master-Slave mode can avoid colision?

Karl Ylvisaker — Thu, 24 Feb 2022 11:05:15 GMT

[quote user="zhangkui"]We have tested that the data throughput of multifold is less than one master connect two slaves. Maybe the reason is we set both connect interval and event length 7.5ms.[/quote]

What parameters did you use in your other tests, and what throughput did you achieve in both tests?

Best regards,
Karl

RE: BLE Master-Slave mode can avoid colision?

zhangkui — Thu, 24 Feb 2022 10:55:25 GMT

Ok, We have tested that the data throughput of multifold is less than one master connect two slaves. Maybe the reason is we set both connect interval and event length 7.5ms. Can you give us some suggestion about setting for multitoles

RE: BLE Master-Slave mode can avoid colision?

Karl Ylvisaker — Thu, 24 Feb 2022 09:33:13 GMT

I can confirm that there will not be collisions between the radio usage of the different roles when the timeslot API is used to separate the two. The timeslot API is made for this specific reason, so that you can be certain that the radio is available to the specific role/function at a specific time. The connection sequence will not matter as long as both roles are provided an appropriate timeslot.

Best regards,
Karl

RE: BLE Master-Slave mode can avoid colision?

zhangkui — Thu, 24 Feb 2022 02:19:20 GMT

you think nordic can avoid colision in both cases(multifold connect master device first or connect slave device first)? We only set proper event length and connect interval. SDK can avoid collision.-------connect sequence have no effect.

Or connect sequined is very important.

RE: BLE Master-Slave mode can avoid colision?

zhangkui — Thu, 24 Feb 2022 02:03:13 GMT

So I want to confirm if the multirole device connect the slave device first , Can Nordic avoid the colision. We have test that it can't. But I think if the multirole device connect the master device first , It will be different.

Can you help confirm it?

RE: BLE Master-Slave mode can avoid colision?

Karl Ylvisaker — Wed, 23 Feb 2022 08:39:42 GMT

Hello,

Yes, the SoftDevice will handle this for you as detailed in the SoftDevice scheduling documentation.
When the SoftDevice is working in the multirole configuration (both central and peripheral role) it will use the Timeslot API to makes sure that there are no collision between the radio usage of each role.

Best regards,
Karl