Directed advertising - peer address

Question

Hello everyone

I am using BLE Peripheral UART and Central UART samples to send data between two nrf5340 dev. kits.

I'm trying to set the directed advertising on the peripheral, so it accepts only connections request from my peer, but I can't find, in which format should i set the address of the central. I tried to change it this way in peripheral main, but it did not connect.

err = bt_le_adv_start(((struct bt_le_adv_param[]) { 
{ .id = BT_ID_DEFAULT, .sid = 0, .secondary_max_skip = 0, 
.options = (BT_LE_ADV_OPT_CONNECTABLE), .interval_min = (0x00a0), 
.interval_max = (0x00f0), .peer = {0xF0,0x33,0x4D,0x3A,0x9F,0x6B}, } }),
ad, ARRAY_SIZE(ad), sd, ARRAY_SIZE(sd));

I am also a little bit confused of the Bluetooth LE Device Adress in addr.h library.

/** Bluetooth Device Address */
typedef struct {
	uint8_t  val[BT_ADDR_SIZE];
} bt_addr_t;
/**/

/** Length in bytes of an LE Bluetooth address. Not packed, so no sizeof() */
#define BT_ADDR_LE_SIZE 7
/** Bluetooth LE Device Address */
typedef struct {
	uint8_t      type;
	bt_addr_t a;
} bt_addr_le_t;

What does the variable type mean and in which way should I write the bt_addr_t?

Here is the log from J-Link RTT Viewer

00> [00:00:00.272,583] <inf> fs_nvs: 2 Sectors of 4096 bytes
00> [00:00:00.272,583] <inf> fs_nvs: alloc wra: 0, fc8
00> [00:00:00.272,583] <inf> fs_nvs: data wra: 0, 2c
00> [00:00:00.300,354] <inf> bt_hci_core: No ID address. App must call settings_load()
00> [00:00:00.300,354] <inf> peripheral_uart: Bluetooth initialized
00> [00:00:00.949,981] <inf> peripheral_uart: Connected F0:33:4D:3A:9F:6B (random)
00> [00:00:01.664,978] <wrn> peripheral_uart: Failed to send data over BLE connection

Could please somebody help me or give me any advice?

Sorry for maybe stupid questions, I am just beginner and did not find it anywhere.

AHaug · Accepted Answer

Hi Jirik, 
 Now we need some kind of filtering of what centrals the peripherals should be interested in connecting to. As a default, the central and peripheral samples are set up to connect to each other based on the service UUID-filter I mentioned in my previous reply (or the device name as I did in the modified sample), but the peripheral also advertises to the world and everyone nearby that the peripheral is connectable, thus you are able to connect to it with your phone. 
 One option to exclude every other central from connecting to the peripheral might be direct advertising but I haven't looked into this yet, so lets look into the option of whitelisting first. This part is a bit tricky as you state there are little to no guides on how to do this in NCS (hopefully some will come). In addition to this, the whitelisting functionality mentioned in the webinar is deprecated in NCS to my knowledge, and " bt_le_filter_accept_list_add()" from " ble_adv.c" located in " ncs\v1.9.1
rf\subsys\caf\modules", together with the config setting " CONFIG_BT_FILTER_ACCEPT_LIST=y " is used. I have not fully managed to set up a sample that does this, but I will continue to work on it during this week whenever I have time, so I will supply it to you if I finish it. In the meanwhile I will give you some pointers to where you may continue to work. 
 To do what you describe you need to do the following: 
 
 Investigate " ble_adv.c" located in " ncs\v1.9.1
rf\subsys\caf\modules". bt_le_filter_accept_list_add() should let you set up a list of device addresses that your peripheral accepts the connection initiation from. 
 Obtain the address or set the address of the Central device . You may do this by setting up a Wireshark BLE sniffer . When the setup is done, you can filter the scanning on the peripheral address, which you can obtain in nRF Connect for Mobile as seen in the picture below. This will let you see all the advertisements, scan responses and scan requests coming to this device. What we're looking for is the device that initiates your connection, which will be the central, in my case the address c2:04:4b:0c:72:3b 
 Set up a whitelist of the device that the peripheral should connect to. Use the functionality mentioned in 1) together with 2) 
 
 Some more "philosophical" things to consider, albeit not necessarily relevant for the question you're asking. Depending on the scale of operation you are aiming to work on this might not be the best solution. If you're working with a low number of devices, i.e a couple of devices on your desk, this should be no problem at all. But if you're creating a product that should be scaled up several magnitudes you should consider setting up a more scripted/automated way of doing this. In addition to this, if you aim on whitelisting a mobile phone as a central, you will most likely require additional functionality such as bonding and encryption when whitelisting. But both of these are modules that can be added after the whitelisting is working properly if they are necessary! 
 As mentioned, I will keep on investigating how the whitelisting works with a simple sample and supply it if I get it to work! Let me know about your progress if you manage to set it up yourself with these pointers and if you have any additional questions! Edit: I believe this case supported by a colleague of mine might also be of help! The customer seems to have a similar question to you regarding limiting the devices that should be able to connect to your device Kind regards, Andreas

Directed advertising - peer address

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