Two centrals both scanning

RE: Two centrals both scanning

awneil — Mon, 26 Oct 2020 22:46:19 GMT

You don't need it - you can do it in your firmware.

RE: Two centrals both scanning

Joe — Mon, 26 Oct 2020 22:41:36 GMT

Awneil, my difficulty is I don't have access to the firmware outside the Nordic chip.

RE: Two centrals both scanning

awneil — Mon, 26 Oct 2020 22:36:20 GMT

[quote userid="18670" url="~/f/nordic-q-a/67580/two-centrals-both-scanning/276980#276980"]My issue is the stack reports it is connected, but it may not really be[/quote]

My suggestion would avoid you getting into that situation at all.

RE: Two centrals both scanning

Joe — Mon, 26 Oct 2020 22:25:57 GMT

Hi Kenneth,

It looks like the sd_ble_gap_connect() takes the parameters from sdk_config.h.
#define NRF_BLE_SCAN_MIN_CONNECTION_INTERVAL 7.5
#define NRF_BLE_SCAN_MAX_CONNECTION_INTERVAL 30
#define NRF_BLE_SCAN_SLAVE_LATENCY 0
#define NRF_BLE_SCAN_SUPERVISION_TIMEOUT 2000
They are already very small values, if I reduce them to smaller value, the firmware will halt.

You mentioned the 6 connection intervals, is it a parameter I can change?

My issue is the stack reports it is connected, but it may not really be. Is there a reliable way to detect the connection is really made after the SCAN REQUEST?

Thanks.

RE: Two centrals both scanning

Kenneth — Mon, 26 Oct 2020 14:50:02 GMT

If a connection request is sent from the central, then the central will try 6 connection intervals before giving up (;connection failed to establish), so you can for instance set the initial (minimum) connection interval to something shorter than 80-100ms? When trying to connect to a peripheral, it may also be good to set a reasonable timeout value (e.g. 1-2seconds), in case the peripheral is no longer in range or turned OFF. Both these parameters are set when calling sd_ble_gap_connect().

Best regards,
Kenneth

RE: Two centrals both scanning

awneil — Fri, 23 Oct 2020 22:58:04 GMT

[quote userid="18670" url="~/f/nordic-q-a/67580/two-centrals-both-scanning/276725#276725"]Both centrals says they are connected[/quote]

I think that's the point from the linked thread: they say 'connected' as soon as they have requested the connection - but that's before the connection has been completely established.

Again, I think the safest approach would be to have something at your Central end decide on which one - and only one - of your nRF52832s is going to make the connection.

RE: Two centrals both scanning

Joe — Fri, 23 Oct 2020 22:52:08 GMT

Thank you for the link. I don't get a BLE_HCL_CONN_FAILED_TO_BE_ESTABLISHED, it would be good if I do. I poll for events for more than a second after they are connected, and don't see any event that indicates problem. Both centrals says they are connected, but one take a lot longer than the other one to connect.

RE: Two centrals both scanning

awneil — Fri, 23 Oct 2020 22:21:27 GMT

[quote userid="18670" url="~/f/nordic-q-a/67580/two-centrals-both-scanning/276721#276721"] I am surprise the second central can connect to it after the first one since the peripheral should stop the advertisement after the connection.[/quote]

Of course, they will both see the advertising.

Then they might both try to initiate connecting at the "same" time - but only one will actually succeed to fully establish the connection. The other one will just time out, because the peripheral will not accept the connection.

I would guess that you are getting a BLE_HCI_CONN_FAILED_TO_BE_ESTABLISHED - as described here: https://devzone.nordicsemi.com/f/nordic-q-a/40808/connect-procedure-and-the-disconnect-reason-0x3e-ble_hci_conn_failed_to_be_established ?

[quote userid="18670" url="~/f/nordic-q-a/67580/two-centrals-both-scanning/276721#276721"] I hope to find something in the Central side which is my Nordic code to tell if it is the second connection or invalid connection,[/quote]

Again, I think you need one of your Centrals to make the decision on which of the two is to initiate the connection.

Or, maybe, a 3rd processor to make the decision?

Or perhaps you could have only one of them scanning - and it will tell the other the necessary details of the peripheral(s) for it to connect to ?

RE: Two centrals both scanning

Joe — Fri, 23 Oct 2020 22:10:27 GMT

The two centrals are in the same enclosure. Actually, I am surprise the second central can connect to it after the first one since the peripheral should stop the advertisement after the connection. I saw from the MultiPeripheral example, that when NRF_SDH_BLE_PERIPHERAL_LINK_COUNT is set to more than 1, a peripheral can connect to multiple centrals at the same time? Not sure how the advertisement work in that case.

The peripheral is a third party device so I have little control over the parameters. I hope to find something in the Central side which is my Nordic code to tell if it is the second connection or invalid connection, and abort from it.

RE: Two centrals both scanning

awneil — Fri, 23 Oct 2020 21:58:39 GMT

[quote userid="18670" url="~/f/nordic-q-a/67580/two-centrals-both-scanning"]two nRF52832 side by side scanning for advertisement[/quote]

You mean they are physically located together - on the same board, or in the same enclosure?

Perhaps you could make one of them the "master" and have it decide which of the two nRF52832s is to attempt to make the connection to each peripheral ?