The scan observer stops getting called after a failed attempt to connect to a peripheral using whitelist.

RE: The scan observer stops getting called after a failed attempt to connect to a peripheral using whitelist.

ovrebekk — Tue, 16 Nov 2021 13:49:51 GMT

Hi again

Ignore my last reply.

I realize that I made one (possibly critical) change to the code you sent me: I changed the NRF_BLE_SCAN_SCAN_DURATION in sdk_config.h from 0 to 1000.

I noticed that the scan parameters are passed along to the sd_ble_gap_connect(..) function, which means that if you have unlimited scan duration (timeout) you also have unlimited timeout when trying to connect to a device.

Could you try to change the scan_duration to a non zero number as well?

Then the connection attempt should time out like I described in my earlier response.

Please note that when using a scan timeout you need to restart scanning manually once it times out, in case you want scanning to run continuously.

Best regards
Torbjørn

RE: The scan observer stops getting called after a failed attempt to connect to a peripheral using whitelist.

ovrebekk — Tue, 16 Nov 2021 13:29:54 GMT

Are you able to share your latest version of your code with me, so I can test it out here?

I am basing my test on the code you sent earlier, and with the changes I made I am unable to get it to lock up.

Best regards
Torbjørn

RE: The scan observer stops getting called after a failed attempt to connect to a peripheral using whitelist.

Skara — Fri, 12 Nov 2021 10:19:27 GMT

Hi Torbjørn,

I did place that code in the on_ble_evt function but it never gets called.

As I've written previously, I am logging all events that come. I do log them in the ble_evt_handler function which is the observer for ble events. I also log them in the nrf_sdh_ble_evts_poll function. After the sd_ble_gap_connect that returns success there are no more events coming.

https://ibb.co/Wgp2KPg

In the picture above you can see after I start the scanning device it finds lots of ble devices which do not match the filter. Than I turn on the second board which is advertising only and right after I see the 'Connection status: 0' log, I unplug the advertising device. At that point the scanning device is already hanging. There are no more logs coming until I start the advertising device again.

Cheers,
Skara

RE: The scan observer stops getting called after a failed attempt to connect to a peripheral using whitelist.

ovrebekk — Thu, 11 Nov 2021 14:41:52 GMT

Hi Skara

Could you try to add the following code to the on_ble_evt(..) function, inside the switch case?

case BLE_GAP_EVT_TIMEOUT:
    // The issue occurs when the connection times out, in which case scanning hasn't been started when we think it has
    if (p_ble_evt->evt.gap_evt.params.timeout.src == BLE_GAP_TIMEOUT_SRC_CONN)
    {
        NRF_LOG_DEBUG("Connection Request timed out. Restart scanning...");
        nrf_ble_scan_start(&m_scan);
    }
    break;

Best regards
Torbjørn

RE: The scan observer stops getting called after a failed attempt to connect to a peripheral using whitelist.

Skara — Wed, 10 Nov 2021 08:32:56 GMT

Hey Torbjørn,

no worries :) Thank you for taking your time, to help solving my issue.

I'm not sure I understand exactly what you mean.

As I already mentioned, I restart the scanner on CONNECTED/DISCONNECTED events. In my case the application gets stuck somewhere after a connection attempt is being made in the nrf_ble_scan_connect_with_target function, where sd_ble_gap_connect is called and it returns success. There are no more events after that to which I can react.

I do have NRF_SDH_BLE_LOG_ENABLED and the NRF_LOG_LEVEL set to Debug so I can see all the events coming to that module, but after that sd_ble_gap_connect where my app gets stuck, there are no more events.

My application restarts the scanner manually after about a minute where I get the NRF_ERROR_INVALID_STATE response but still no events are logged.

Where and when exactly should I be expecting/handling this BLE_GAP_EVT_TIMEOUT?

Thank you!
Skara

RE: The scan observer stops getting called after a failed attempt to connect to a peripheral using whitelist.

ovrebekk — Tue, 09 Nov 2021 14:30:35 GMT

Hi Skara

My deepest apologies. It has been some busy months here, and I forgot to follow up on your case. Thanks a lot for the reminder.

Debugging this further it seems the problem is related to the missed handling of the BLE_GAP_EVT_TIMEOUT event.

I tried to track if any BLE events were sent after the occurrence of the "Are we scanning or not" situation, and found that the only BLE event I could see was the BLE_GAP_EVT_TIMEOUT event.
This event signals that the connection attempt failed, but is not being picked up by any of the event handlers in the application, or by the scan module.

The scan module only responds to this event when the timeout source is BLE_GAP_TIMEOUT_SRC_SCAN, but in this case the source is BLE_GAP_TIMEOUT_SRC_CONN because it is a connection that times out.

In your main file I notice that there is some log output if the event is passed to the on_ble_central_evt(..) function, but since the role is set to BLE_GAP_ROLE_INVALID the event will not be forwarded here.

Could you try to start scanning manually if the BLE_GAP_EVT_TIMEOUT event occurs with source set to BLE_GAP_TIMEOUT_SRC_CONN and role set to BLE_GAP_ROLE_INVALID?

I believe this should solve the issue.

Best regards
Torbjørn

RE: The scan observer stops getting called after a failed attempt to connect to a peripheral using whitelist.

Skara — Mon, 08 Nov 2021 12:48:40 GMT

Hi Torbjørn,

were you able to find anything new regarding this issue?

Thanks
Sakra

RE: The scan observer stops getting called after a failed attempt to connect to a peripheral using whitelist.

ovrebekk — Fri, 22 Oct 2021 11:31:47 GMT

Hi Skara

In my case I was running an app_timer that would try to start scanning at 5 second intervals. This would recover the stack after the issue occurred, but obviously this is not an ideal workaround.

It could be interesting to try and set a flag when the issue occurs, and check this flag in main. Once the flag is set you try to start scanning again from main context.

I will have to spend some more time with this, and will try to get you an update early next week.

Best regards
Torbjørn

RE: The scan observer stops getting called after a failed attempt to connect to a peripheral using whitelist.

Skara — Thu, 21 Oct 2021 13:44:32 GMT

Hey,

indeed I do see the "Are we scanning or not?" output when the device ends up in this state. Do you know why is the device entering this invalid state and how can I recover in that case?

Detecting this state might be a bit of a problem in my application though. I do start the scanner every time I get a BLE_GAP_EVT_CONNECTED or BLE_GAP_EVT_DISCONNECTED event. Since the stack is stuck and no events are sent out, the scanner will not be restarted.

In my tests I use a timer that restarts the scanner upon timeout and that is when I see the "Are we scanning or not?" message.

By the way I have the same behavior when using SDK12.3 on the central.

Thank you again for your help.
Skara

RE: The scan observer stops getting called after a failed attempt to connect to a peripheral using whitelist.

ovrebekk — Wed, 20 Oct 2021 12:34:33 GMT

Hi again

Thanks a lot for the patience. After spending more time with this I believe I have tracked the issue down to the nrf_ble_scan_start() function, which is set up to ignore the NRF_ERROR_INVALID_STATE error when calling sd_ble_gap_scan_start(..) to restart the scan.

I made the following small modification to the nrf_ble_scan_start() function (to log when INVALID_STATE is returned), and notice that before the stack ends up in the 'stuck' state I see the "Are we scanning or not??" message printed.

ret_code_t nrf_ble_scan_start(nrf_ble_scan_t const * const p_scan_ctx)
{
    VERIFY_PARAM_NOT_NULL(p_scan_ctx);

    ret_code_t err_code;
    scan_evt_t scan_evt;

    memset(&scan_evt, 0, sizeof(scan_evt));

    nrf_ble_scan_stop();

    // If the whitelist is used and the event handler is not NULL, send the whitelist request to the main application.
    if (is_whitelist_used(p_scan_ctx))
    {
        if (p_scan_ctx->evt_handler != NULL)
        {
            scan_evt.scan_evt_id = NRF_BLE_SCAN_EVT_WHITELIST_REQUEST;
            p_scan_ctx->evt_handler(&scan_evt);
        }
    }

    // Start the scanning.
    err_code = sd_ble_gap_scan_start(&p_scan_ctx->scan_params, &p_scan_ctx->scan_buffer);

    // It is okay to ignore this error, because the scan stopped earlier.
    if ((err_code != NRF_ERROR_INVALID_STATE) && (err_code != NRF_SUCCESS))
    {
        NRF_LOG_ERROR("sd_ble_gap_scan_start returned 0x%x", err_code);
        return (err_code);
    }
    else if(err_code == NRF_ERROR_INVALID_STATE)
    {
        NRF_LOG_INFO("Are we scanning or not????");
    }
    NRF_LOG_DEBUG("Scanning");

    return NRF_SUCCESS;
}

Could you try to make the same change on your end, make sure that logging is enabled for the scan module, and see if you also get this message when the problem occurs?

Best regards
Torbjørn

RE: The scan observer stops getting called after a failed attempt to connect to a peripheral using whitelist.

ovrebekk — Mon, 11 Oct 2021 14:17:08 GMT

Hi Skara

Thanks for the added details. I have been able to reproduce the issue now. It seems the SoftDevice is somehow getting stuck when trying to connect to the device, but I haven't been able to find a way to solve it yet.

I will have to look more into this and get back to you later.

Best regards
Torbjørn

RE: The scan observer stops getting called after a failed attempt to connect to a peripheral using whitelist.

Skara — Thu, 07 Oct 2021 14:22:50 GMT

Hi Torbjørn,

the whitelist is only activated/applied if there are already bonded peers. So before starting the central I used the mobile nrf connect app to bond to the peripheral. Than just restart the peripheral and power the central on and you should be able to reproduce it.

Thanks
Skara

RE: The scan observer stops getting called after a failed attempt to connect to a peripheral using whitelist.

ovrebekk — Thu, 07 Oct 2021 12:48:58 GMT

Hi Skara

How is the whitelist set in your test?

I added some logging every time the set_whitelist() function is run, and see that it never finds any peers to add to the list.

In my test the two devices will just enter into an infinite connecting-> starting pairing-> timing out on passkey confirmation -> disconnecting -> reconnecting loop.

As soon as I turn off the peripheral the scanner proceeds to pick up other advertise packets.

Maybe I also need to run one of your other peripherals to reproduce the issue?

Best regards
Torbjørn

RE: The scan observer stops getting called after a failed attempt to connect to a peripheral using whitelist.

Skara — Tue, 05 Oct 2021 09:49:19 GMT

Hey Torbjørn,

in my actual application I will have multiple different peripherals to which the central will try to connect to as soon as it sees any of them.

In this trace I filtered only the packets of the peripheral that the central is trying to connect to. The trace was made in a very noisy environment with more than 20 advertising BLE devices of which only one advertises the filtered UUID.

As I've written in my initial post, I did add a logging call in the observer function nrf_ble_scan_on_adv_report() which prints the addresses of the peripherals from which packets were received. Before powering on the peripheral, this log is coming continuously showing the addresses of many different devices. After the failed pair/bond and powering off the peripheral no log is to be seen as the observer function is never called again.

Best
Skara

RE: The scan observer stops getting called after a failed attempt to connect to a peripheral using whitelist.

ovrebekk — Tue, 05 Oct 2021 08:20:39 GMT

Hi Skara

What are these other devices that you are trying to connect to?

Shouldn't they also show up in the sniffer trace, if they are advertising at the same time as the whitelist peripheral?

I can take a look at your code, but it would be good to know a bit more about the various devices you are using in your test.

Best regards
Torbjørn

RE: The scan observer stops getting called after a failed attempt to connect to a peripheral using whitelist.

Skara — Mon, 04 Oct 2021 09:48:13 GMT

Hi,

I did not stop the trace but switched the peripheral device off.

The problem is that at that point the central seems to be stuck somewhere and since the observer never gets called again it can not initiate connections to other devices. The observer only gets called again if I turn the same peripheral back on and it starts advertising again.

Here are the slightly modified ble_central_and_peripheral projects that I use to reproduce it.

devzone.nordicsemi.com/.../ble_5F00_app_5F00_multirole_5F00_lesc.tar.gz

Cheers
Skara

RE: The scan observer stops getting called after a failed attempt to connect to a peripheral using whitelist.

ovrebekk — Mon, 04 Oct 2021 09:30:16 GMT

Hi Skara

Thanks for sharing the trace.

I can't really spot anything problematic there. The central tries to connect three times, and fails each time (because of the whitelist I assume).

After the third connection attempt there is no more activity in the trace. Is this because you stopped the trace, or was there no more activity over the air?

Best regards
Torbjørn

RE: The scan observer stops getting called after a failed attempt to connect to a peripheral using whitelist.

Skara — Fri, 01 Oct 2021 11:36:40 GMT

Hi Torbjørn,

sure, here is the capture of multiple connection attempts.
devzone.nordicsemi.com/.../connect_5F00_non_5F00_whitelisted_5F00_device.pcapng

RE: The scan observer stops getting called after a failed attempt to connect to a peripheral using whitelist.

ovrebekk — Fri, 01 Oct 2021 10:38:20 GMT

Hi Skara

Any chance you could provide a sniffer trace when this issue occurs?

Assuming you have an nRF52DK to spare you can run that as a sniffer, using the nRF Sniffer application.

Best regards
Torbjørn