Pairing unsuccessful with phone

[vn2000]

I designed a reduced size PCB that used an nRF52832 and will act as a BLE HID device.

With the original nRF52DK evaluation board I was able to use the example ble_app_hids_mouse SDK V15 and pair it with Android and iPhones.

But when I used the new PCB with ble_app_hids_mouse, It only worked 1 out of 15 or 20 tries. Otherwise I got the message 'Pairing Unsuccessful: Pairing takes too long..'. However this new PCB works with other non-hid examples such as ble_app_hrs. I did try another commercial unit such as the 'Red Bear Nano' and it has the same issue as mine.

It seems like a hardware issue at first. However I noticed is that even the Nordic nRF52DK eval board has the same issue with SDK V11 (pairing unsuccessful). The nRF52DK board works better with SDK V15 and ble_app_hids_mouse. 

My question is what is mainly required for in a pairing process? Is there a way I can modify any parameter to ease the condition for pairing, such as the number of peers, white list, etc.. to make it work? Since the PCB worked fine with other applications that don't require pairing.

[Hakon]

Hello,

are you trying to make the ble_app_hids_mouse example in sdk 11 work on your custom board?

[vn2000]

Yes. First I want to see if the ble_app_hids_mouse example (unchanged) in sdk works on my PCB. I tried both V11 and V15. I also tried with a commercial unit, the Red Bear Nano BLE, and have the same problem. They don't work neither with V11 nor V15 ble_app_hids_mouse. But they still work with other non-hid app that don't require pairing.

However, The nRF52DK eval board works with V15 but not V11 (ble_app_hids_mouse).

We badly need Nordic nRF52 to work as a BLE HID device. That will be our main product.

[Hakon]

Does it also happen with the ble_app_hids_keyboard example?

[vn2000]

Interestingly, the ble_app_hids_keyboard can be paired with the iPhone only once. After that the pairing was mostly unsuccessful, just like the ble_app_hids_mouse.

The ble_app_hids_keyboard is not even seen by Android phone when I go to Settings->Bluetooth. At least with ble_app_hids_mouse I can see it in both Android and iPhone, even though pairing was unsuccessful.

What I can see here is that both ble_app_hids_mouse and ble_app_hids_keyboard were able to pair only once the first time the firmware was loaded into flash. Then after that the pairing was always unsuccessful. It looks like some variables were initialized correctly at first. Then after that they affected the subsequent pairing process that prevented it from being paired again.

[Hakon]

Change the line

advertising_start(erase_bonds);

in main.c to

advertising_start(1);

and see if you are able to pair every time.

[vn2000]

I changed to advertising_start(1) but still have the same issue: Pairing Unsuccessful.

When I used this new compiled firmware, the original nRF52DK can't pair either.

[Hakon]

Ok, try erasing the chip then reprogram (and remember to flash the soft device). Do this everytime you try reconnecting.

[Hakon]

I think I know how to deal with the "Pairing Unsuccessful" problem now. What worked for me was adding

        case PM_EVT_CONN_SEC_CONFIG_REQ:
        {
            pm_conn_sec_config_t conn_sec_config = {.allow_repairing = true};
            pm_conn_sec_config_reply(p_evt->conn_handle, &conn_sec_config);
        } break;

to pm_evt_handler().

Also, every time you reset the device, press button 2, or if you don't want to press the button every time you reset you can change to advertising_start(1) as described below.

[vn2000]

I do have these statements in PM_EVT_CONN_SEC_CONFIG_REQ, even though it looks like:

conn_sec_config.allow_repairing = true;
pm_conn_sec_config_reply(p_evt->conn_handle, &conn_sec_config);

My PCB doesn't have button 2. So I used advertising_start(1) at reset. But pairing is still unsuccessful.

Since I'm displaying serial debug messages, I was following up some variables and I noticed that when the pairing is successful, the value of m_whitelist_peer_cnt  to be 2 or 3. When the pairing is unsuccessful, m_whitelist_peer_cnt   is always 1. This value is set by the function pm_peer_id_list, called by whitelist_set in advertising start.

I'm trying to trace further, but if you can give a suggestion that will help.