How to discover a service, disconnect from it and discover another one ?

Question

CS_prog.zip RSSI_prog.zip 
 Hello, 
 I'm working on Windows 11, with the nRF Connect for VS Code v2025.5.512 extension, with ncs v3.0.2. I'm using the nRF54L15-dk (PCA10156; 0.9.2; 2025.7) development kits. 
 So, I want to use the channel sounding sample to measure a distance and then send a data if it's below a threshold. I first tried to implement that program with the BLE RSSI instead of using the CS and it works well (cf. RSSI_execution picture). 
 So my question is how to discover a service, disconnect from it and discover another one ? 
 Since the CS is using a service, I want to first discover the ranging service then if the measured distance is below the threshold, I want do discover my custom service to send my data. I tried discovering my custom service at the beginning and at the end of the loop that gets the distance in the main (while(true)) but then either it doesn't want to measure the distance and it sends the value directly or it gets the distance but can't send the data. (cf custom_begin and custom_end pictures respectively). 
 Do you know how I can fix those errors ? I've put my programs and pictures in the zip folders below for both the RSSI and the CS. 
 Thanks and best regards, 
 Patrick

Edvin · Answer

Looking at your cs_initiator5.c, it seems like you start the discovery process in your connected_cb() function. 
 Your question is a bit diffuse to me. Your peripheral (reflector) should contain all the services and characteristics at all times. But it is up to your applications when you want to use them. When you connect, start the service discovery, which should store all the characteristic handles. 
 
 I see that you are using bt_gatt_discover() directly. This is possible, but perhaps you should consider using bt_gatt_dm_start() instead, which is a bit more abstracted. This is used in the NCS
rf\samples\bluetooth\central_uart sample. Then you will get a discovery complete callback: 
 static void discovery_complete(struct bt_gatt_dm *dm,
 void *context)
{
	struct bt_nus_client *nus = context;
	LOG_INF("Service discovery completed");

	bt_gatt_dm_data_print(dm);

	bt_nus_handles_assign(dm, nus);
	bt_nus_subscribe_receive(nus);

	bt_gatt_dm_data_release(dm);
} 
 If you initialize the discovery parameters with service UUID = NULL, it will give you a callback for each service. So you just add handlers for all characteristics that you want to use, that checks if it is the correct service, and if so, register the handle. E.g. if you want to register the NUS (Nordic uart service) and an additional service called "CUS" (Custom service), you can have something like this: 
 static void discovery_complete(struct bt_gatt_dm *dm,
 void *context)
{
	struct bt_nus_client *nus = context;
	LOG_INF("Service discovery completed");

	bt_gatt_dm_data_print(dm);

	bt_nus_handles_assign(dm, nus);
	bt_nus_subscribe_receive(nus);
	bt_cus_handles_assign(dm, cus);
	bt_cus_subscribe_receive(cus);

	bt_gatt_dm_data_release(dm);
} 
 
 You can see in the implementation of e.g. bt_nus_handles_assign() in nus_client.c that the first thing it does is checking the UUID: 
 int bt_nus_handles_assign(struct bt_gatt_dm *dm,
 struct bt_nus_client *nus_c)
{
	const struct bt_gatt_dm_attr *gatt_service_attr =
 bt_gatt_dm_service_get(dm);
	const struct bt_gatt_service_val *gatt_service =
 bt_gatt_dm_attr_service_val(gatt_service_attr);
	const struct bt_gatt_dm_attr *gatt_chrc;
	const struct bt_gatt_dm_attr *gatt_desc;

	if (bt_uuid_cmp(gatt_service->uuid, BT_UUID_NUS_SERVICE)) {
 return -ENOTSUP;
	}
	... 
 And returns if the UUID is not the BT_UUID_NUS_SERVICE, so when it is called on another service that is discovered, it will just ignore that service. 
 
 Once all your services are discovered, you can use them from wherever you prefer in your application. 
 
 Best regards, 
 Edvin

How to discover a service, disconnect from it and discover another one ?

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