Connecting to Pi/Bleno with sd_ble_gap_connect

[Gordon]

Hi,

I'm trying to connect to a Raspberry Pi from an nRF52832 via BLE Central mode. The Pi is running a node.js app (via bleno) and I can connect and communicate with it just fine using the nRF Connect app.

I can use sd_ble_gap_scan_start and can see the device advertising itself, however when I use sd_ble_gap_connect to connect using its mac address, nothing happens (it just times out).

I can connect fine to other nRF52832-based devices though.

I'm using:

  static ble_gap_scan_params_t     m_scan_param;
  memset(&m_scan_param, 0, sizeof(m_scan_param));
  m_scan_param.active       = 0;            // Active scanning set.
  m_scan_param.interval     = MSEC_TO_UNITS(100, UNIT_0_625_MS); // Scan interval.
  m_scan_param.window       = MSEC_TO_UNITS(100, UNIT_0_625_MS); // Scan window.
  m_scan_param.timeout      = 4;            // 4 second timeout.

  static ble_gap_conn_params_t   gap_conn_params;
  memset(&gap_conn_params, 0, sizeof(gap_conn_params));
  gap_conn_params.min_conn_interval = MSEC_TO_UNITS(7.5, UNIT_1_25_MS);
  gap_conn_params.max_conn_interval = MSEC_TO_UNITS(75, UNIT_1_25_MS);
  gap_conn_params.slave_latency     = 0;
  gap_conn_params.conn_sup_timeout  = MSEC_TO_UNITS(4000, UNIT_10_MS);

  err_code = sd_ble_gap_connect(&addr, &m_scan_param, &gap_conn_params);

The only obvious difference I can find is the Pi comes up in nRF connect as GeneralDiscoverable whereas other nRF devices are LimitedDiscoverable.

Any thoughts? A longer (or no) timeout doesn't help matters.

Also, I was occasionally getting NRF_ERROR_INVALID_PARAM before I made the arguments static, but I'm not getting it after. Is that a red herring? I'd prefer not to make things static if it's not required.

[Gordon]

I also noticed that some examples set active to 1, but I seem to get NRF_ERROR_INVALID_PARAM every time I use it unless the parameters are static. Even when I do it, I still can't get a connection from the Pi though.

[Petter Myhre]

I don't see why they would need to be static. I need to check the behavior, what SDK and SoftDevice version are you using? Are you sure the address and the address type is correct?

[Gordon]

I'm using SDK12 with the 3.0.0 softdevice. Thanks! Address type was the issue! I was using BLE_GAP_ADDR_TYPE_RANDOM_STATIC, and if I changed to BLE_GAP_ADDR_TYPE_PUBLIC it worked (but then it no longer worked when accessing one of the nRF devices).

What's the difference? Is it to do with Limited/GeneralDiscoverable? I was hoping to expose this as an API to a user, where they could just supply an address like "d1:53:36:1a:7a:17" - but is that actually workable?

[Petter Myhre]

See this for differences between the address types, more information can be found in the Bluetooth spec. You need to supply the correct address type in addition to the actual address.

[Gordon]

Thanks - that's really helpful. I'd just assumed addresses were unique. Looks like I need to change the API then!