Find and Subscribe to multiple BT Characteristics

[finkbr]

Hi,

I've tried a lot of different things.  Occasionally I've had promising results where I actually fine and subscribe to a single characteristic.  Most recently I've tried gatt_dm with no results, it finds service 1801 with 4 characteristics, then 1800 with 7 characteristics then errors out with Not enough memory for next attribute descriptor at handle 40.  

My Prj.conf file contains CONFIG_BT_GATT_DM_MAX_ATTRS=350 per another persons post with a similar problem.  The peripheral I'm connecting to from my central app has A LOT of characteristics (unfortunately I have to connect to it and deal with the issues of having a lot of characteristics (310))

I've tried this but it doesn't find all of the characteristics for some reason.  it will find one and subscribe to one as well but I have 5 I need to subscribe to as well as several i need handles to that i need to write to.

I am using NCS v2.2.0 on Windows 10 the nRF52832 is on a custom board, I've looked at central_HR and haven't really gotten anything to work.  I believe gatt_dm will do what I need but I need to figure out why it wont find more than 40 attributes.

Brian

[Edvin]

Hello Brian,

Can you please describe in a bit more detail what you are seeing? What happens when not all characteristics show up? Does the central application crash?

Best regards,

Edvin

[finkbr]

When i try and find all services first (like the code in the link I referenced) i find all the services.  BUT when it moved to characteristics, it only finds between 5 and 10 characteristics.  I am leaving the UUID set at NULL so from my understanding it should return all characteristics.  when finished with characteristics, it finds the CCCD's and finds 3 (correct number).  

What happens when not all characteristics show up?  Nothing, everything runs to completion.  No errors no indications that anything odd has happened.

When i tried the central app, it does crash, I put in a ticket for that and didn't get a response before i went to central_gatt.  central gatt does not crash.  so I've been working off that as a base.  

Currently ive modified everything to this:

switch(discover_phase) {
        case DISC_PHASE_SERVICE:
            if(attr) {
				// Getting here, attr->uuid will be BT_UUID_GATT_PRIMARY 
				struct bt_gatt_service_val *svc_attr = attr->user_data;
				memcpy(uuid_str,BT_UUID_128(svc_attr->uuid)->val,16);
				printk("UID: %02x%02x%02x%02x-%02x%02x-%02x%02x-%02x%02x-%02x%02x%02x%02x%02x%02x\n",uuid_str[15],uuid_str[14],uuid_str[13],uuid_str[12],uuid_str[11],uuid_str[10],uuid_str[9],uuid_str[8],uuid_str[7],uuid_str[6],uuid_str[5],uuid_str[4],uuid_str[3],uuid_str[2],uuid_str[1],uuid_str[0]);
				printk("attr is a primary service.  UUID type is %d, val = %x\n", svc_attr->uuid->type, BT_UUID_16(svc_attr->uuid)->val);
				if(!bt_uuid_cmp(svc_attr->uuid, BT_UUID_DRONE_RX_SERVICE))
				{
					printk("FOUND DRONE_RX SVC\n\n");
					dront_rx_svc_handle = attr->handle;
					discover_params.type = BT_GATT_DISCOVER_CHARACTERISTIC;
                	discover_params.start_handle = last_handle + 1;
					err = bt_gatt_discover(conn, &discover_params);
					if (err) {
						printk("Discover failed - svc (err %d)\n", err);
					}
					last_handle = attr->handle;
					discover_phase = DISC_PHASE_CHRC;
					return BT_GATT_ITER_STOP;
					}
					last_handle = attr->handle;
            }
            else {
                // No more service UUIDs.  Look for Characteristics. 
                printk("No more services, looking for characteristics\n");
                discover_params.uuid = NULL;
				//memcpy(uuid_str,BT_UUID_128(discover_params.uuid)->val,16);
				//printk("DISCOVER UID: %02x%02x%02x%02x-%02x%02x-%02x%02x-%02x%02x-%02x%02x%02x%02x%02x%02x\n",uuid_str[15],uuid_str[14],uuid_str[13],uuid_str[12],uuid_str[11],uuid_str[10],uuid_str[9],uuid_str[8],uuid_str[7],uuid_str[6],uuid_str[5],uuid_str[4],uuid_str[3],uuid_str[2],uuid_str[1],uuid_str[0]);
                discover_params.type = BT_GATT_DISCOVER_CHARACTERISTIC;
                discover_params.start_handle = last_handle + 1;

                err = bt_gatt_discover(conn, &discover_params);
                if (err) {
                    printk("Discover failed - svc (err %d)\n", err);
                }
                discover_phase = DISC_PHASE_CHRC;
                return BT_GATT_ITER_STOP;
            }
			return BT_GATT_ITER_CONTINUE;
            break;

		case DISC_PHASE_CHRC:
            if(attr) 
			{
				// Getting here, attr->uuid will be BT_UUID_GATT_CHRC 
				struct bt_gatt_chrc *chrc_attr = attr->user_data;
				memcpy(uuid_str,BT_UUID_128(chrc_attr->uuid)->val,16);
				printk("UID: %02x%02x%02x%02x-%02x%02x-%02x%02x-%02x%02x-%02x%02x%02x%02x%02x%02x\n",uuid_str[15],uuid_str[14],uuid_str[13],uuid_str[12],uuid_str[11],uuid_str[10],uuid_str[9],uuid_str[8],uuid_str[7],uuid_str[6],uuid_str[5],uuid_str[4],uuid_str[3],uuid_str[2],uuid_str[1],uuid_str[0]);
				printk("attr is a characteristic.  UUID type is %d, val = %x\n", chrc_attr->uuid->type, BT_UUID_16(chrc_attr->uuid)->val);

				
				
                last_handle = attr->handle;
            }
            else {
                // Ran out of characteristics, look for CCCDs 
                printk("No more characteristics, looking for CCCDs\n");
                //discover_params.type = BT_GATT_DISCOVER_DESCRIPTOR;
        		//discover_params.start_handle = attr->handle + 1;
                //discover_params.start_handle = last_handle + 1;

                //err = bt_gatt_discover(conn, &discover_params);
                //if (err) {
                //    printk("Discover failed - chrc (err %d)\n", err);
                //}
                //discover_phase = DISC_PHASE_CCCD;
                return BT_GATT_ITER_STOP;
            }
			return BT_GATT_ITER_CONTINUE;
            break;
	}
}

it selects a service, then looks for characteristics.  it then finds ALL of the characteristics BUT not all of the services.  Changing the code to not stop at my specific service <BT_UUID_DRONE_RX_SERVICE> results  in all services being found but only 3 characteristics for the LAST service only.

What i need to do is capture 2 services and about 5 characteristics from each for reading and writing.  Finding the DRONE_RX_SERVICE and switching to characteristic discovery then doesn't find the TX_SERVICE.  

I am a novice at this and its been a struggle to find appropriate documentation that says what happens when.  such as if you stop iterating at a service you cant go back to iterating through services anymore.  the gatt_dm seems like it does what i want/need but i cant get that to work at all.  My co-worker has done this stuff before however he did it before zephyr and a lot has changed apparently because he is struggling too.

[Edvin]

I don't know what I am looking at. Where is this snippet placed? 

[finkbr]

This is the connected function:

static void connected(struct bt_conn *conn, uint8_t conn_err)
{
	struct bt_conn_info conn_info;
	char addr[BT_ADDR_LE_STR_LEN];
	int err;

	bt_addr_le_to_str(bt_conn_get_dst(conn), addr, sizeof(addr));
	LOG_DBG("Connecting to: %s", addr);

	if (conn_err) {
		LOG_DBG("%s: Failed to connect to %s (%u)\n", __func__, addr,
		       conn_err);
		return;
	}
	else {
		LOG_DBG("Connected to (%s)\n",addr);
	}

	err = bt_conn_get_info(conn, &conn_info);
	if (err) {
		LOG_DBG("Failed to get connection info (%d).\n", err);		
		return;
	}

	LOG_DBG("%s: %s role %u\n", __func__, addr, conn_info.role);

	conn_connected = bt_conn_ref(conn);

	//(void)mtu_exchange(conn);

#if defined(CONFIG_BT_SMP)
	if (conn_info.role == BT_CONN_ROLE_CENTRAL) {
		err = bt_conn_set_security(conn, BT_SECURITY_L2);
		if (err) {
			printk("Failed to set security (%d).\n", err);
		}
	}
#endif

	//err = bt_gatt_dm_start(conn, NULL, &discover_all_cb, NULL);
	//if (err) {
		//printk("Failed to start discovery (err %d)\n", err);
	//}
	if (conn == conn_connected) {		
		discover_params.uuid = NULL;
		discover_params.func = discover_services;
		discover_params.start_handle = BT_ATT_FIRST_ATTRIBUTE_HANDLE;
		discover_params.end_handle = BT_ATT_LAST_ATTRIBUTE_HANDLE;
		discover_params.type = BT_GATT_DISCOVER_PRIMARY;
		discover_phase = DISC_PHASE_SERVICE;

		err = bt_gatt_discover(conn_connected, &discover_params);
		if (err)
		{
			printk("Discover failed(err %d)\n", err);
			return;
		}	
		printk("end of discover in connect\n");

	}
}

I set discovered_params.func to discover_services.  The snippet above is from discovered_services.  Here it is in its entirety

uint8_t discover_services(struct bt_conn *conn, const struct bt_gatt_attr *attr, struct bt_gatt_discover_params *params)
{
	int err;
	static uint16_t last_handle;
	char uuid_str[16];
	
	if(attr) 
	{		
        printk("[ATTRIBUTE] handle %u\n", attr->handle);	
		printk("uuid type = %d, val=%x\n", attr->uuid->type,BT_UUID_16(attr->uuid)->val);	  
	}

	switch(discover_phase) {
        case DISC_PHASE_SERVICE:
            if(attr) {
				// Getting here, attr->uuid will be BT_UUID_GATT_PRIMARY 
				struct bt_gatt_service_val *svc_attr = attr->user_data;
				memcpy(uuid_str,BT_UUID_128(svc_attr->uuid)->val,16);
				printk("UID: %02x%02x%02x%02x-%02x%02x-%02x%02x-%02x%02x-%02x%02x%02x%02x%02x%02x\n",uuid_str[15],uuid_str[14],uuid_str[13],uuid_str[12],uuid_str[11],uuid_str[10],uuid_str[9],uuid_str[8],uuid_str[7],uuid_str[6],uuid_str[5],uuid_str[4],uuid_str[3],uuid_str[2],uuid_str[1],uuid_str[0]);
				printk("attr is a primary service.  UUID type is %d, val = %x\n", svc_attr->uuid->type, BT_UUID_16(svc_attr->uuid)->val);
				if(!bt_uuid_cmp(svc_attr->uuid, BT_UUID_DRONE_RX_SERVICE))
				{
					printk("FOUND DRONE_RX SVC\n\n");
					drone_rx_svc_handle = attr->handle;
					discover_params.type = BT_GATT_DISCOVER_CHARACTERISTIC;
                	discover_params.start_handle = last_handle + 1;
					err = bt_gatt_discover(conn, &discover_params);
					if (err) {
						printk("Discover failed - svc (err %d)\n", err);
					}
					last_handle = attr->handle;
					discover_phase = DISC_PHASE_CHRC;
					return BT_GATT_ITER_STOP;
				}
				
				last_handle = attr->handle;
            }
            else {
                // No more service UUIDs.  Look for Characteristics. 
                printk("No more services, looking for characteristics\n");
                discover_params.uuid = NULL;
				//memcpy(uuid_str,BT_UUID_128(discover_params.uuid)->val,16);
				//printk("DISCOVER UID: %02x%02x%02x%02x-%02x%02x-%02x%02x-%02x%02x-%02x%02x%02x%02x%02x%02x\n",uuid_str[15],uuid_str[14],uuid_str[13],uuid_str[12],uuid_str[11],uuid_str[10],uuid_str[9],uuid_str[8],uuid_str[7],uuid_str[6],uuid_str[5],uuid_str[4],uuid_str[3],uuid_str[2],uuid_str[1],uuid_str[0]);
                discover_params.type = BT_GATT_DISCOVER_CHARACTERISTIC;
                discover_params.start_handle = last_handle + 1;

                err = bt_gatt_discover(conn, &discover_params);
                if (err) {
                    printk("Discover failed - svc (err %d)\n", err);
                }
				last_handle=attr->handle;
                discover_phase = DISC_PHASE_CHRC;
                return BT_GATT_ITER_STOP;
            }
			return BT_GATT_ITER_CONTINUE;
            break;

		case DISC_PHASE_CHRC:
            if(attr) 
			{
				// Getting here, attr->uuid will be BT_UUID_GATT_CHRC 
				struct bt_gatt_chrc *chrc_attr = attr->user_data;
				memcpy(uuid_str,BT_UUID_128(chrc_attr->uuid)->val,16);
				printk("UID: %02x%02x%02x%02x-%02x%02x-%02x%02x-%02x%02x-%02x%02x%02x%02x%02x%02x\n",uuid_str[15],uuid_str[14],uuid_str[13],uuid_str[12],uuid_str[11],uuid_str[10],uuid_str[9],uuid_str[8],uuid_str[7],uuid_str[6],uuid_str[5],uuid_str[4],uuid_str[3],uuid_str[2],uuid_str[1],uuid_str[0]);
				printk("attr is a characteristic.  UUID type is %d, val = %x\n", chrc_attr->uuid->type, BT_UUID_16(chrc_attr->uuid)->val);

				if(!bt_uuid_cmp(chrc_attr->uuid,BT_UUID_DRONE_TX_SERVICE))
				{
					printk("FOUND DRONE_TX SVC\n\n");
					drone_tx_svc_handle = attr->handle;
				}
				if(!bt_uuid_cmp(chrc_attr->uuid, BT_UUID_DRONE_RX_NOACK))
				{	
					LOG_DBG("FOUND DRONE RX NOACK 0A\n\n");
					drone_rx0a_handle = attr->handle;                	
				}
				if(!bt_uuid_cmp(chrc_attr->uuid, BT_UUID_DRONE_TX_ACK))
				{	
					LOG_DBG("FOUND DRONE TX ACK FB0E\n\n");
					drone_rx0a_handle = attr->handle;                	
				}
				
				last_handle = attr->handle;
            }
            else {
                // Ran out of characteristics, look for CCCDs 
                printk("No more characteristics, looking for CCCDs\n");
                discover_params.type = BT_GATT_DISCOVER_DESCRIPTOR;
        		discover_params.start_handle = attr->handle + 1;
                discover_params.start_handle = last_handle + 1;

                err = bt_gatt_discover(conn, &discover_params);
                if (err) {
                    printk("Discover failed - chrc (err %d)\n", err);
                }
                discover_phase = DISC_PHASE_CCCD;
                return BT_GATT_ITER_STOP;
            }
			
			return BT_GATT_ITER_CONTINUE;
            break;
		case DISC_PHASE_CCCD:
            if(attr) {
				memcpy(uuid_str,BT_UUID_128(attr->uuid)->val,16);
				printk("UID: %02x%02x%02x%02x-%02x%02x-%02x%02x-%02x%02x-%02x%02x%02x%02x%02x%02x\n",uuid_str[15],uuid_str[14],uuid_str[13],uuid_str[12],uuid_str[11],uuid_str[10],uuid_str[9],uuid_str[8],uuid_str[7],uuid_str[6],uuid_str[5],uuid_str[4],uuid_str[3],uuid_str[2],uuid_str[1],uuid_str[0]);
               
                printk("attr is a CCCD.  UUID type is %d, val = %x\n", attr->uuid->type, BT_UUID_16(attr->uuid)->val);
                if(attr->user_data == NULL) {
                    printk("user_data is NULL\n");
                }
                else {
                    struct bt_gatt_ccc *dope = attr->user_data;
					
                    printk("user data is %x\n", dope->flags);
                }
                // Check if this CCCD is associated with Report charact 
                //if(!bt_uuid_cmp(attr->uuid, &cis_report_char_uuid.uuid)) {
                //    printk("Found CCCD for Report characteristic\n");
                //    cccd_handle = attr->handle;
                //}
                last_handle = attr->handle;
            }
            else {
                printk("Discovery complete\n");
               
            }
            break;
    
	}
}

Its not pretty, ive been trying to get things to work.  

How about answering this question: How does the iteration work.  It seems that when you're looking for just services, it is scanning ALL of the services, characteristics, CCCD's etc.  so if you get to the end of the list with services and THEN look for characteristics they are no longer available to iterate through. 

What exactly does BT_GATT_ITER_CONTINUE and BT_GATT_ITER_STOP do?  Does it stop at the current iteration point and return then allow you to restart somewhere else in the list or ???  I've been looking for a definition of how this iteration of characteristics and services works but haven't found one.

My latest attempt at finding characteristics and services is to find the first service and then switch to characteristics and when I find the UUID of a service or characteristic I need then I simply record the handle and continue.  Once I finish, hopefully it'll work, ill try and get that done and tested today.

Brian 

[finkbr]

So after a lot of iterations i seem to now be able to get the 2 services and 8 characteristics i want to monitor.  Here is my final bit of code:

The connect function:

static void connected(struct bt_conn *conn, uint8_t conn_err)
{
	struct bt_conn_info conn_info;
	char addr[BT_ADDR_LE_STR_LEN];
	int err;

	bt_addr_le_to_str(bt_conn_get_dst(conn), addr, sizeof(addr));
	LOG_DBG("Connecting to: %s", addr);

	if (conn_err) {
		LOG_DBG("%s: Failed to connect to %s (%u)\n", __func__, addr,
		       conn_err);
		return;
	}
	else {
		LOG_DBG("Connected to (%s)\n",addr);
	}

	err = bt_conn_get_info(conn, &conn_info);
	if (err) {
		LOG_DBG("Failed to get connection info (%d).\n", err);		
		return;
	}

	LOG_DBG("%s: %s role %u\n", __func__, addr, conn_info.role);

	conn_connected = bt_conn_ref(conn);

	//(void)mtu_exchange(conn);

#if defined(CONFIG_BT_SMP)
	if (conn_info.role == BT_CONN_ROLE_CENTRAL) {
		err = bt_conn_set_security(conn, BT_SECURITY_L2);
		if (err) {
			printk("Failed to set security (%d).\n", err);
		}
	}
#endif
	
	if (conn == conn_connected) {		
		discover_params.uuid = NULL;
		discover_params.func = discover_services;
		discover_params.start_handle = BT_ATT_FIRST_ATTRIBUTE_HANDLE;
		discover_params.end_handle = BT_ATT_LAST_ATTRIBUTE_HANDLE;
		discover_params.type = BT_GATT_DISCOVER_PRIMARY;
		discover_phase = DISC_PHASE_SERVICE;

		err = bt_gatt_discover(conn_connected, &discover_params);
		if (err)
		{
			printk("Discover failed(err %d)\n", err);
			return;
		}	
		printk("end of discover in connect\n");

	}
}

And the discover_services function:

uint8_t discover_services(struct bt_conn *conn, const struct bt_gatt_attr *attr, struct bt_gatt_discover_params *params)
{
	int err;
	static uint16_t last_handle;
	char uuid_str[16];
	
	if(attr) 
	{		
        printk("[ATTRIBUTE] handle %u\n", attr->handle);	
		printk("uuid type = %d, val=%x\n", attr->uuid->type,BT_UUID_16(attr->uuid)->val);	  
	}
	switch(discover_phase) 
	{
        case DISC_PHASE_SERVICE:
            if(attr) {
				// Getting here, attr->uuid will be BT_UUID_GATT_PRIMARY 
				struct bt_gatt_service_val *svc_attr = attr->user_data;
				memcpy(uuid_str,BT_UUID_128(svc_attr->uuid)->val,16);
				printk("UID: %02x%02x%02x%02x-%02x%02x-%02x%02x-%02x%02x-%02x%02x%02x%02x%02x%02x\n",uuid_str[15],uuid_str[14],uuid_str[13],uuid_str[12],uuid_str[11],uuid_str[10],uuid_str[9],uuid_str[8],uuid_str[7],uuid_str[6],uuid_str[5],uuid_str[4],uuid_str[3],uuid_str[2],uuid_str[1],uuid_str[0]);
				printk("attr is a primary service.  UUID type is %d, val = %x\n", svc_attr->uuid->type, BT_UUID_16(svc_attr->uuid)->val);
				if(!bt_uuid_cmp(svc_attr->uuid, BT_UUID_DRONE_RX_SERVICE))
				{
					printk("FOUND DRONE_RX SVC\n\n");
					drone_rx_svc_handle = attr->handle;
					return BT_GATT_ITER_CONTINUE;
				}

				if(!bt_uuid_cmp(svc_attr->uuid, BT_UUID_DRONE_TX_SERVICE))
				{
					printk("FOUND DRONE_TX SVC\n\n");
					drone_tx_svc_handle = attr->handle;
					discover_params.type = BT_GATT_DISCOVER_CHARACTERISTIC;
                	discover_params.start_handle = last_handle + 1;
					err = bt_gatt_discover(conn, &discover_params);
					if (err) {
						printk("Discover failed - svc (err %d)\n", err);
					}
					last_handle = attr->handle;
					discover_phase = DISC_PHASE_CHRC;
					return BT_GATT_ITER_STOP;
				}
				last_handle = attr->handle;
				
            }
            else {
                // No more service UUIDs.  Look for Characteristics. 
                printk("No more services, looking for characteristics\n");
                discover_params.type = BT_GATT_DISCOVER_CHARACTERISTIC;
                discover_params.start_handle = last_handle + 1;

                err = bt_gatt_discover(conn, &discover_params);
                if (err) {
                    printk("Discover failed - svc (err %d)\n", err);
                }
				last_handle=attr->handle;
                discover_phase = DISC_PHASE_CHRC;
                return BT_GATT_ITER_STOP;
            }           

		case DISC_PHASE_CHRC:
            if(attr) 
			{
				// Getting here, attr->uuid will be BT_UUID_GATT_CHRC 
				struct bt_gatt_chrc *chrc_attr = attr->user_data;
				
				memcpy(uuid_str,BT_UUID_128(chrc_attr->uuid)->val,16);
				printk("UID: %02x%02x%02x%02x-%02x%02x-%02x%02x-%02x%02x-%02x%02x%02x%02x%02x%02x\n",uuid_str[15],uuid_str[14],uuid_str[13],uuid_str[12],uuid_str[11],uuid_str[10],uuid_str[9],uuid_str[8],uuid_str[7],uuid_str[6],uuid_str[5],uuid_str[4],uuid_str[3],uuid_str[2],uuid_str[1],uuid_str[0]);
				
				printk("attr is a characteristic.  UUID type is %d, val = %x\n", chrc_attr->uuid->type, BT_UUID_16(chrc_attr->uuid)->val);

				
				if(!bt_uuid_cmp(chrc_attr->uuid, BT_UUID_DRONE_RX_NOACK))
				{	
					LOG_DBG("FOUND DRONE RX NOACK FA0A\n\n");
					drone_rx0a_handle = attr->handle;        
					LOG_DBG("rx0a handle: %u ",drone_rx0a_handle);         	
				}
				if(!bt_uuid_cmp(chrc_attr->uuid, BT_UUID_DRONE_RX_ACK))
				{	
					LOG_DBG("FOUND DRONE RX NOACK FA0B\n\n");
					drone_rx0b_handle = attr->handle;          
					LOG_DBG("rx0b handle: %u ",drone_rx0b_handle);        	
				}
				if(!bt_uuid_cmp(chrc_attr->uuid, BT_UUID_DRONE_RX_HIPRI_ACK))
				{	
					LOG_DBG("FOUND DRONE RX HIPRO FA0C\n\n");
					drone_rx0c_handle = attr->handle;                	
					LOG_DBG("rx0c handle: %u ",drone_rx0c_handle);  
				}
				if(!bt_uuid_cmp(chrc_attr->uuid, BT_UUID_DRONE_RX_STATE))
				{	
					LOG_DBG("FOUND DRONE RX STATE FA0E\n\n");
					drone_rx0e_handle = attr->handle;                	
					LOG_DBG("rx0e handle: %u ",drone_rx0e_handle);  
				}
				if(!bt_uuid_cmp(chrc_attr->uuid, BT_UUID_DRONE_RX_ACK_ACK))
				{	
					LOG_DBG("FOUND DRONE RX ACKACK FA1E\n\n");
					drone_rx1e_handle = attr->handle;    
					LOG_DBG("rx1e handle: %u ",drone_rx1e_handle);              	
				}
				if(!bt_uuid_cmp(chrc_attr->uuid, BT_UUID_DRONE_TX_ACK))
				{	
					LOG_DBG("FOUND DRONE TX ACK FB0E\n\n");
					drone_tx0e_handle = attr->handle;      
					LOG_DBG("tx0e handle: %u ",drone_tx0e_handle); 
					subscribe_params.notify = notify_cb;
					subscribe_params.value = BT_GATT_CCC_NOTIFY;
					subscribe_params.ccc_handle = drone_tx0e_handle;

					err = bt_gatt_subscribe(conn, &subscribe_params);
					if (err && err != -EALREADY) {
						printk("Subscribe failed (err %d)\n", err);
					} else {
						printk("[SUBSCRIBED ACK 0E]\n");
					} 
				}
				if(!bt_uuid_cmp(chrc_attr->uuid, BT_UUID_DRONE_TX_NOACK))
				{	
					LOG_DBG("FOUND DRONE TX NOACK FB0F\n\n");

					drone_tx0f_handle = attr->handle;       
					LOG_DBG("tx0f handle: %u ",drone_tx0f_handle); 
					subscribe_params.notify = notify_cb;
					subscribe_params.value = BT_GATT_CCC_NOTIFY;
					subscribe_params.ccc_handle = drone_tx0f_handle;

					err = bt_gatt_subscribe(conn, &subscribe_params);
					if (err && err != -EALREADY) {
						printk("Subscribe failed (err %d)\n", err);
					} else {
						printk("[SUBSCRIBED NOACK 0F]\n");
					} 
				}
				if(!bt_uuid_cmp(chrc_attr->uuid, BT_UUID_DRONE_TX_ACK_ACK))
				{	
					LOG_DBG("FOUND DRONE TX ACKACK FB1B\n\n");
					drone_tx1b_handle = attr->handle;       
					LOG_DBG("tx1b handle: %u ",drone_tx1b_handle); 
					subscribe_params.notify = notify_cb;
					subscribe_params.value = BT_GATT_CCC_NOTIFY;
					subscribe_params.ccc_handle = drone_tx1b_handle;

					err = bt_gatt_subscribe(conn, &subscribe_params);
					if (err && err != -EALREADY) {
						printk("Subscribe failed (err %d)\n", err);
					} else {
						printk("[SUBSCRIBED ACK ACK 1B]\n");
					} 
				}
				if(!bt_uuid_cmp(chrc_attr->uuid, BT_UUID_DRONE_TX_HIPRI_ACK))
				{	
					LOG_DBG("FOUND DRONE TX HIPRI FB1C\n\n");
					drone_tx1c_handle = attr->handle;       
					LOG_DBG("tx1c handle: %u ",drone_tx1c_handle); 
					subscribe_params.notify = notify_cb;
					subscribe_params.value = BT_GATT_CCC_NOTIFY;
					subscribe_params.ccc_handle = drone_tx1c_handle;

					err = bt_gatt_subscribe(conn, &subscribe_params);
					if (err && err != -EALREADY) {
						printk("Subscribe failed (err %d)\n", err);
					} else {
						printk("[SUBSCRIBED HIPRI 1C]\n");
					} 
				}

				last_handle = attr->handle;
            }
            else {
                // Ran out of characteristics, look for CCCDs 
                printk("No more characteristics, looking for CCCDs\n");
                discover_params.type = BT_GATT_DISCOVER_DESCRIPTOR;        		
                discover_params.start_handle = last_handle + 1;

                err = bt_gatt_discover(conn, &discover_params);
                if (err) {
                    printk("Discover failed - chrc (err %d)\n", err);
                }
                discover_phase = DISC_PHASE_CCCD;
                return BT_GATT_ITER_STOP;
            }			
			
            
		case DISC_PHASE_CCCD:
            if(attr) {
				memcpy(uuid_str,BT_UUID_128(attr->uuid)->val,16);
				printk("UID: %02x%02x%02x%02x-%02x%02x-%02x%02x-%02x%02x-%02x%02x%02x%02x%02x%02x\n",uuid_str[15],uuid_str[14],uuid_str[13],uuid_str[12],uuid_str[11],uuid_str[10],uuid_str[9],uuid_str[8],uuid_str[7],uuid_str[6],uuid_str[5],uuid_str[4],uuid_str[3],uuid_str[2],uuid_str[1],uuid_str[0]);
               
                printk("attr is a CCCD.  UUID type is %d, val = %x\n", attr->uuid->type, BT_UUID_16(attr->uuid)->val);
                if(attr->user_data == NULL) {
                    printk("user_data is NULL\n");
                }
                else {
                    struct bt_gatt_ccc *dope = attr->user_data;
					
                    printk("user data is %x\n", dope->flags);
                }
                // Check if this CCCD is associated with Report charact 
                //if(!bt_uuid_cmp(attr->uuid, &cis_report_char_uuid.uuid)) {
                //    printk("Found CCCD for Report characteristic\n");
                //    cccd_handle = attr->handle;
                //}
                last_handle = attr->handle;
            }
            else {
               printk("Discovery complete\n");
               return BT_GATT_ITER_STOP;
            }
            break;
		
    
	}
	return BT_GATT_ITER_CONTINUE;
	
}

What im not sure i did correctly is the placement of the BT_GATT_ITER_CONTINUE and BT_GATT_ITER_STOP returns.  And I am also not sure i have done the notify_cb correctly.  I write to FA0A with this write command:

LOG_DBG("sending data to %u",drone_rx0a_handle);
	err = bt_gatt_write_without_response(conn, drone_rx0a_handle, data, data_len,false);
	if (err) {
		printk("%s: Write cmd failed (%d).\n", __func__, err);
	}

and I would expect my notify_cb function to be called but it isnt.

here is the notify_cb:

uint8_t notify_cb(struct bt_conn *conn, struct bt_gatt_subscribe_params *params,  const void *data, uint16_t length)
{
	if (!data) {
		printk("[UNSUBSCRIBED]\n");
		params->value_handle = 0U;
	}

	printk("[NOTIFICATION] data %p length %u\n", data, length);

	return BT_GATT_ITER_CONTINUE;
}

Out of the 4 characteristics i subscribe to (I can see the [SUBSCRIBED] in the RTT output, 2 get [UNSUBSCRIBED] while characteristics are being found

Here is a listing of the output on RTT of all of the debug:

[00:00:21.301,025] <dbg> gatt_common: connected: connected: D0:3A:A7:09:E6:20 (random) role 0

end of discover in connect
[ATTRIBUTE] handle 1
uuid type = 0, val=2800
UID: fb000000-0020-007c-6820-007c6818011b
attr is a primary service.  UUID type is 0, val = 1801
UID: fb000000-0020-007c-6820-007c6818011b
attr is a characteristic.  UUID type is 0, val = 1801
UID: 00200044-0400-0200-0420-004424280000
attr is a CCCD.  UUID type is 0, val = 2800
user data is 4424
[ATTRIBUTE] handle 16
uuid type = 0, val=2800
UID: fb000000-0020-007c-6820-007c6818001b
attr is a primary service.  UUID type is 0, val = 1800
UID: fb000000-0020-007c-6820-007c6818001b
attr is a characteristic.  UUID type is 0, val = 1800
UID: 00200044-0400-0200-1620-004424280000
attr is a CCCD.  UUID type is 0, val = 2800
user data is 4424
[ATTRIBUTE] handle 32
uuid type = 0, val=2800
UID: 9a66fa00-0800-9191-11e4-012d1540cb8e
attr is a primary service.  UUID type is 2, val = 40cb
FOUND DRONE_RX SVC

[ATTRIBUTE] handle 144
uuid type = 0, val=2800
UID: 9a66fb00-0800-9191-11e4-012d1540cb8e
attr is a primary service.  UUID type is 2, val = 40cb
FOUND DRONE_TX SVC

[00:00:22.000,946] <dbg> central_gatt: central_gatt_write: Calling write
[00:00:22.001,403] <dbg> gatt_common: write_cmd: sending data to 0
[00:00:22.001,953] <dbg> gatt_common: write_cmd: data sent
security_changed: to level 2 (err 0)
[ATTRIBUTE] handle 17
uuid type = 0, val=2803
UID: 05000000-0000-0028-0000-02aea82a0044
attr is a characteristic.  UUID type is 0, val = 2a00
UID: 31000000-0020-0021-4820-0019f8280300
attr is a CCCD.  UUID type is 0, val = 2803
user data is 4428
[ATTRIBUTE] handle 19
uuid type = 0, val=2803
UID: 05000000-0000-0028-0000-02aea82a0144
attr is a characteristic.  UUID type is 0, val = 2a01
UID: 31000000-0020-0021-4820-0019f8280300
attr is a CCCD.  UUID type is 0, val = 2803
user data is 4428
[ATTRIBUTE] handle 21
uuid type = 0, val=2803
UID: 05000000-0000-0028-0000-02aea82a0444
attr is a characteristic.  UUID type is 0, val = 2a04
UID: 31000000-0020-0021-4820-0019f8280300
attr is a CCCD.  UUID type is 0, val = 2803
user data is 4428
[ATTRIBUTE] handle 33
uuid type = 0, val=2803
UID: 9a66fa00-0800-9191-11e4-012d1540cb8e
attr is a characteristic.  UUID type is 2, val = 40cb
UID: 31000000-0020-0021-4820-0019f8280300
attr is a CCCD.  UUID type is 0, val = 2803
user data is 4428
[ATTRIBUTE] handle 36
uuid type = 0, val=2803
UID: 9a66fa01-0800-9191-11e4-012d1540cb8e
attr is a characteristic.  UUID type is 2, val = 40cb
UID: 31000000-0020-0021-4820-0019f8280300
attr is a CCCD.  UUID type is 0, val = 2803
user data is 4428
[ATTRIBUTE] handle 39
uuid type = 0, val=2803
UID: 9a66fa02-0800-9191-11e4-012d1540cb8e
attr is a characteristic.  UUID type is 2, val = 40cb
UID: 31000000-0020-0021-4820-0019f8280300
attr is a CCCD.  UUID type is 0, val = 2803
user data is 4428
[ATTRIBUTE] handle 42
uuid type = 0, val=2803
UID: 9a66fa03-0800-9191-11e4-012d1540cb8e
attr is a characteristic.  UUID type is 2, val = 40cb
UID: 31000000-0020-0021-4820-0019f8280300
attr is a CCCD.  UUID type is 0, val = 2803
user data is 4428
[ATTRIBUTE] handle 45
uuid type = 0, val=2803
UID: 9a66fa04-0800-9191-11e4-012d1540cb8e
attr is a characteristic.  UUID type is 2, val = 40cb
UID: 31000000-0020-0021-4820-0019f8280300
attr is a CCCD.  UUID type is 0, val = 2803
user data is 4428
[ATTRIBUTE] handle 48
uuid type = 0, val=2803
UID: 9a66fa05-0800-9191-11e4-012d1540cb8e
attr is a characteristic.  UUID type is 2, val = 40cb
UID: 31000000-0020-0021-4820-0019f8280300
attr is a CCCD.  UUID type is 0, val = 2803
user data is 4428
[ATTRIBUTE] handle 51
uuid type = 0, val=2803
UID: 9a66fa06-0800-9191-11e4-012d1540cb8e
attr is a characteristic.  UUID type is 2, val = 40cb
UID: 31000000-0020-0021-4820-0019f8280300
attr is a CCCD.  UUID type is 0, val = 2803
user data is 4428
[ATTRIBUTE] handle 54
uuid type = 0, val=2803
UID: 9a66fa07-0800-9191-11e4-012d1540cb8e
attr is a characteristic.  UUID type is 2, val = 40cb
UID: 31000000-0020-0021-4820-0019f8280300
attr is a CCCD.  UUID type is 0, val = 2803
user data is 4428
[ATTRIBUTE] handle 57
uuid type = 0, val=2803
UID: 9a66fa08-0800-9191-11e4-012d1540cb8e
attr is a characteristic.  UUID type is 2, val = 40cb
UID: 31000000-0020-0021-4820-0019f8280300
attr is a CCCD.  UUID type is 0, val = 2803
user data is 4428
[ATTRIBUTE] handle 60
uuid type = 0, val=2803
UID: 9a66fa09-0800-9191-11e4-012d1540cb8e
attr is a characteristic.  UUID type is 2, val = 40cb
UID: 31000000-0020-0021-4820-0019f8280300
attr is a CCCD.  UUID type is 0, val = 2803
user data is 4428
[ATTRIBUTE] handle 63
uuid type = 0, val=2803
UID: 9a66fa0a-0800-9191-11e4-012d1540cb8e
attr is a characteristic.  UUID type is 2, val = 40cb
[00:00:23.302,215] <dbg> central_gatt: discover_services: FOUND DRONE RX NOACK FA0A


[00:00:23.302,734] <dbg> central_gatt: discover_services: rx0a handle: 63 
UID: 31000000-0020-0021-4820-0019f8280300
attr is a CCCD.  UUID type is 0, val = 2803
user data is 4428
[ATTRIBUTE] handle 66
uuid type = 0, val=2803
UID: 9a66fa0b-0800-9191-11e4-012d1540cb8e
attr is a characteristic.  UUID type is 2, val = 40cb
[00:00:23.402,221] <dbg> central_gatt: discover_services: FOUND DRONE RX NOACK FA0B


[00:00:23.402,740] <dbg> central_gatt: discover_services: rx0b handle: 66 
UID: 31000000-0020-0021-4820-0019f8280300
attr is a CCCD.  UUID type is 0, val = 2803
user data is 4428
Updated MTU: TX: 247 RX: 247 bytes
le_param_req: int (0x0006, 0x0006) lat 0 to 500
[ATTRIBUTE] handle 69
uuid type = 0, val=2803
UID: 9a66fa0c-0800-9191-11e4-012d1540cb8e
attr is a characteristic.  UUID type is 2, val = 40cb
[00:00:23.502,532] <dbg> central_gatt: discover_services: FOUND DRONE RX HIPRO FA0C


[00:00:23.503,051] <dbg> central_gatt: discover_services: rx0c handle: 69 
UID: 31000000-0020-0021-4820-0019f8280300
attr is a CCCD.  UUID type is 0, val = 2803
user data is 4428
[ATTRIBUTE] handle 72
uuid type = 0, val=2803
UID: 9a66fa0d-0800-9191-11e4-012d1540cb8e
attr is a characteristic.  UUID type is 2, val = 40cb
UID: 31000000-0020-0021-4820-0019f8280300
attr is a CCCD.  UUID type is 0, val = 2803
user data is 4428
[ATTRIBUTE] handle 75
uuid type = 0, val=2803
UID: 9a66fa0e-0800-9191-11e4-012d1540cb8e
attr is a characteristic.  UUID type is 2, val = 40cb
[00:00:23.659,942] <dbg> central_gatt: discover_services: FOUND DRONE RX STATE FA0E


[00:00:23.660,430] <dbg> central_gatt: discover_services: rx0e handle: 75 
UID: 31000000-0020-0021-4820-0019f8280300
attr is a CCCD.  UUID type is 0, val = 2803
user data is 4428
[ATTRIBUTE] handle 78
uuid type = 0, val=2803
UID: 9a66fa0f-0800-9191-11e4-012d1540cb8e
attr is a characteristic.  UUID type is 2, val = 40cb
UID: 31000000-0020-0021-4820-0019f8280300
attr is a CCCD.  UUID type is 0, val = 2803
user data is 4428
[ATTRIBUTE] handle 81
uuid type = 0, val=2803
UID: 9a66fa10-0800-9191-11e4-012d1540cb8e
attr is a characteristic.  UUID type is 2, val = 40cb
UID: 31000000-0020-0021-4820-0019f8280300
attr is a CCCD.  UUID type is 0, val = 2803
user data is 4428
[ATTRIBUTE] handle 84
uuid type = 0, val=2803
UID: 9a66fa11-0800-9191-11e4-012d1540cb8e
attr is a characteristic.  UUID type is 2, val = 40cb
UID: 31000000-0020-0021-4820-0019f8280300
attr is a CCCD.  UUID type is 0, val = 2803
user data is 4428
[ATTRIBUTE] handle 87
uuid type = 0, val=2803
UID: 9a66fa12-0800-9191-11e4-012d1540cb8e
attr is a characteristic.  UUID type is 2, val = 40cb
UID: 31000000-0020-0021-4820-0019f8280300
attr is a CCCD.  UUID type is 0, val = 2803
user data is 4428
[ATTRIBUTE] handle 90
uuid type = 0, val=2803
UID: 9a66fa13-0800-9191-11e4-012d1540cb8e
attr is a characteristic.  UUID type is 2, val = 40cb
UID: 31000000-0020-0021-4820-0019f8280300
attr is a CCCD.  UUID type is 0, val = 2803
user data is 4428
[ATTRIBUTE] handle 93
uuid type = 0, val=2803
UID: 9a66fa14-0800-9191-11e4-012d1540cb8e
attr is a characteristic.  UUID type is 2, val = 40cb
UID: 31000000-0020-0021-4820-0019f8280300
attr is a CCCD.  UUID type is 0, val = 2803
user data is 4428
[ATTRIBUTE] handle 96
uuid type = 0, val=2803
UID: 9a66fa15-0800-9191-11e4-012d1540cb8e
attr is a characteristic.  UUID type is 2, val = 40cb
UID: 31000000-0020-0021-4820-0019f8280300
attr is a CCCD.  UUID type is 0, val = 2803
user data is 4428
[ATTRIBUTE] handle 99
uuid type = 0, val=2803
UID: 9a66fa16-0800-9191-11e4-012d1540cb8e
attr is a characteristic.  UUID type is 2, val = 40cb
UID: 31000000-0020-0021-4820-0019f8280300
attr is a CCCD.  UUID type is 0, val = 2803
user data is 4428
[ATTRIBUTE] handle 102
uuid type = 0, val=2803
UID: 9a66fa17-0800-9191-11e4-012d1540cb8e
attr is a characteristic.  UUID type is 2, val = 40cb
UID: 31000000-0020-0021-4820-0019f8280300
attr is a CCCD.  UUID type is 0, val = 2803
user data is 4428
[ATTRIBUTE] handle 105
uuid type = 0, val=2803
UID: 9a66fa18-0800-9191-11e4-012d1540cb8e
attr is a characteristic.  UUID type is 2, val = 40cb
UID: 31000000-0020-0021-4820-0019f8280300
attr is a CCCD.  UUID type is 0, val = 2803
user data is 4428
[ATTRIBUTE] handle 108
uuid type = 0, val=2803
UID: 9a66fa19-0800-9191-11e4-012d1540cb8e
attr is a characteristic.  UUID type is 2, val = 40cb
UID: 31000000-0020-0021-4820-0019f8280300
attr is a CCCD.  UUID type is 0, val = 2803
user data is 4428
[ATTRIBUTE] handle 111
uuid type = 0, val=2803
UID: 9a66fa1a-0800-9191-11e4-012d1540cb8e
attr is a characteristic.  UUID type is 2, val = 40cb
UID: 31000000-0020-0021-4820-0019f8280300
attr is a CCCD.  UUID type is 0, val = 2803
user data is 4428
[ATTRIBUTE] handle 114
uuid type = 0, val=2803
UID: 9a66fa1b-0800-9191-11e4-012d1540cb8e
attr is a characteristic.  UUID type is 2, val = 40cb
UID: 31000000-0020-0021-4820-0019f8280300
attr is a CCCD.  UUID type is 0, val = 2803
user data is 4428
[ATTRIBUTE] handle 117
uuid type = 0, val=2803
UID: 9a66fa1c-0800-9191-11e4-012d1540cb8e
attr is a characteristic.  UUID type is 2, val = 40cb
UID: 31000000-0020-0021-4820-0019f8280300
attr is a CCCD.  UUID type is 0, val = 2803
user data is 4428
[ATTRIBUTE] handle 120
uuid type = 0, val=2803
UID: 9a66fa1d-0800-9191-11e4-012d1540cb8e
attr is a characteristic.  UUID type is 2, val = 40cb
UID: 31000000-0020-0021-4820-0019f8280300
attr is a CCCD.  UUID type is 0, val = 2803
user data is 4428
[ATTRIBUTE] handle 123
uuid type = 0, val=2803
UID: 9a66fa1e-0800-9191-11e4-012d1540cb8e
attr is a characteristic.  UUID type is 2, val = 40cb
[00:00:23.770,385] <dbg> central_gatt: discover_services: FOUND DRONE RX ACKACK FA1E


[00:00:23.770,874] <dbg> central_gatt: discover_services: rx1e handle: 123 
UID: 31000000-0020-0021-4820-0019f8280300
attr is a CCCD.  UUID type is 0, val = 2803
user data is 4428
[ATTRIBUTE] handle 126
uuid type = 0, val=2803
UID: 9a66fa1f-0800-9191-11e4-012d1540cb8e
attr is a characteristic.  UUID type is 2, val = 40cb
UID: 31000000-0020-0021-4820-0019f8280300
attr is a CCCD.  UUID type is 0, val = 2803
user data is 4428
[ATTRIBUTE] handle 145
uuid type = 0, val=2803
UID: 9a66fb00-0800-9191-11e4-012d1540cb8e
attr is a characteristic.  UUID type is 2, val = 40cb
UID: 31000000-0020-0021-4820-0019f8280300
attr is a CCCD.  UUID type is 0, val = 2803
user data is 4428
[ATTRIBUTE] handle 148
uuid type = 0, val=2803
UID: 9a66fb01-0800-9191-11e4-012d1540cb8e
attr is a characteristic.  UUID type is 2, val = 40cb
UID: 31000000-0020-0021-4820-0019f8280300
attr is a CCCD.  UUID type is 0, val = 2803
user data is 4428
[ATTRIBUTE] handle 151
uuid type = 0, val=2803
UID: 9a66fb02-0800-9191-11e4-012d1540cb8e
attr is a characteristic.  UUID type is 2, val = 40cb
UID: 31000000-0020-0021-4820-0019f8280300
attr is a CCCD.  UUID type is 0, val = 2803
user data is 4428
le_param_updated: int 0x0006 lat 0 to 500
[ATTRIBUTE] handle 154
uuid type = 0, val=2803
UID: 9a66fb03-0800-9191-11e4-012d1540cb8e
attr is a characteristic.  UUID type is 2, val = 40cb
UID: 31000000-0020-0021-4820-0019f828032c
attr is a CCCD.  UUID type is 0, val = 2803
user data is 4428
[ATTRIBUTE] handle 157
uuid type = 0, val=2803
UID: 9a66fb04-0800-9191-11e4-012d1540cb8e
attr is a characteristic.  UUID type is 2, val = 40cb
UID: 31000000-0020-0021-4820-0019f828032c
attr is a CCCD.  UUID type is 0, val = 2803
user data is 4428
[ATTRIBUTE] handle 160
uuid type = 0, val=2803
UID: 9a66fb05-0800-9191-11e4-012d1540cb8e
attr is a characteristic.  UUID type is 2, val = 40cb
UID: 31000000-0020-0021-4820-0019f828032c
attr is a CCCD.  UUID type is 0, val = 2803
user data is 4428
[ATTRIBUTE] handle 163
uuid type = 0, val=2803
UID: 9a66fb06-0800-9191-11e4-012d1540cb8e
attr is a characteristic.  UUID type is 2, val = 40cb
UID: 31000000-0020-0021-4820-0019f828032c
attr is a CCCD.  UUID type is 0, val = 2803
user data is 4428
[ATTRIBUTE] handle 166
uuid type = 0, val=2803
UID: 9a66fb07-0800-9191-11e4-012d1540cb8e
attr is a characteristic.  UUID type is 2, val = 40cb
UID: 31000000-0020-0021-4820-0019f828032c
attr is a CCCD.  UUID type is 0, val = 2803
user data is 4428
[ATTRIBUTE] handle 169
uuid type = 0, val=2803
UID: 9a66fb08-0800-9191-11e4-012d1540cb8e
attr is a characteristic.  UUID type is 2, val = 40cb
UID: 31000000-0020-0021-4820-0019f828032c
attr is a CCCD.  UUID type is 0, val = 2803
user data is 4428
[ATTRIBUTE] handle 172
uuid type = 0, val=2803
UID: 9a66fb09-0800-9191-11e4-012d1540cb8e
attr is a characteristic.  UUID type is 2, val = 40cb
UID: 31000000-0020-0021-4820-0019f828032c
attr is a CCCD.  UUID type is 0, val = 2803
user data is 4428
[ATTRIBUTE] handle 175
uuid type = 0, val=2803
UID: 9a66fb0a-0800-9191-11e4-012d1540cb8e
attr is a characteristic.  UUID type is 2, val = 40cb
UID: 31000000-0020-0021-4820-0019f828032c
attr is a CCCD.  UUID type is 0, val = 2803
user data is 4428
[ATTRIBUTE] handle 178
uuid type = 0, val=2803
UID: 9a66fb0b-0800-9191-11e4-012d1540cb8e
attr is a characteristic.  UUID type is 2, val = 40cb
UID: 31000000-0020-0021-4820-0019f828032c
attr is a CCCD.  UUID type is 0, val = 2803
user data is 4428
[ATTRIBUTE] handle 181
uuid type = 0, val=2803
UID: 9a66fb0c-0800-9191-11e4-012d1540cb8e
attr is a characteristic.  UUID type is 2, val = 40cb
UID: 31000000-0020-0021-4820-0019f828032c
attr is a CCCD.  UUID type is 0, val = 2803
user data is 4428
[ATTRIBUTE] handle 184
uuid type = 0, val=2803
UID: 9a66fb0d-0800-9191-11e4-012d1540cb8e
attr is a characteristic.  UUID type is 2, val = 40cb
UID: 31000000-0020-0021-4820-0019f828032c
attr is a CCCD.  UUID type is 0, val = 2803
user data is 4428
[ATTRIBUTE] handle 187
uuid type = 0, val=2803
UID: 9a66fb0e-0800-9191-11e4-012d1540cb8e
attr is a characteristic.  UUID type is 2, val = 40cb
[00:00:23.918,151] <dbg> central_gatt: discover_services: FOUND DRONE TX ACK FB0E


[00:00:23.918,640] <dbg> central_gatt: discover_services: tx0e handle: 187 
[SUBSCRIBED ACK 0E]
UID: 31000000-0020-0021-4820-0019f828032c
attr is a CCCD.  UUID type is 0, val = 2803
user data is 4428
[ATTRIBUTE] handle 190
uuid type = 0, val=2803
UID: 9a66fb0f-0800-9191-11e4-012d1540cb8e
attr is a characteristic.  UUID type is 2, val = 40cb
[00:00:23.921,386] <dbg> central_gatt: discover_services: FOUND DRONE TX NOACK FB0F


[00:00:23.921,875] <dbg> central_gatt: discover_services: tx0f handle: 190 
[SUBSCRIBED NOACK 0F]
UID: 31000000-0020-0021-4820-0019f828032c
attr is a CCCD.  UUID type is 0, val = 2803
user data is 4428
[ATTRIBUTE] handle 193
uuid type = 0, val=2803
UID: 9a66fb10-0800-9191-11e4-012d1540cb8e
attr is a characteristic.  UUID type is 2, val = 40cb
UID: 31000000-0020-0021-4820-0019f828032c
attr is a CCCD.  UUID type is 0, val = 2803
user data is 4428
[ATTRIBUTE] handle 196
uuid type = 0, val=2803
UID: 9a66fb11-0800-9191-11e4-012d1540cb8e
attr is a characteristic.  UUID type is 2, val = 40cb
UID: 31000000-0020-0021-4820-0019f828032c
attr is a CCCD.  UUID type is 0, val = 2803
user data is 4428
[ATTRIBUTE] handle 199
uuid type = 0, val=2803
UID: 9a66fb12-0800-9191-11e4-012d1540cb8e
attr is a characteristic.  UUID type is 2, val = 40cb
UID: 31000000-0020-0021-4820-0019f828032c
attr is a CCCD.  UUID type is 0, val = 2803
user data is 4428
[ATTRIBUTE] handle 202
uuid type = 0, val=2803
UID: 9a66fb13-0800-9191-11e4-012d1540cb8e
attr is a characteristic.  UUID type is 2, val = 40cb
UID: 31000000-0020-0021-4820-0019f828032c
attr is a CCCD.  UUID type is 0, val = 2803
user data is 4428
[ATTRIBUTE] handle 205
uuid type = 0, val=2803
UID: 9a66fb14-0800-9191-11e4-012d1540cb8e
attr is a characteristic.  UUID type is 2, val = 40cb
UID: 31000000-0020-0021-4820-0019f828032c
attr is a CCCD.  UUID type is 0, val = 2803
user data is 4428
[ATTRIBUTE] handle 208
uuid type = 0, val=2803
UID: 9a66fb15-0800-9191-11e4-012d1540cb8e
attr is a characteristic.  UUID type is 2, val = 40cb
UID: 31000000-0020-0021-4820-0019f828032c
attr is a CCCD.  UUID type is 0, val = 2803
user data is 4428
[ATTRIBUTE] handle 211
uuid type = 0, val=2803
UID: 9a66fb16-0800-9191-11e4-012d1540cb8e
attr is a characteristic.  UUID type is 2, val = 40cb
UID: 31000000-0020-0021-4820-0019f828032c
attr is a CCCD.  UUID type is 0, val = 2803
user data is 4428
[ATTRIBUTE] handle 214
uuid type = 0, val=2803
UID: 9a66fb17-0800-9191-11e4-012d1540cb8e
attr is a characteristic.  UUID type is 2, val = 40cb
UID: 31000000-0020-0021-4820-0019f828032c
attr is a CCCD.  UUID type is 0, val = 2803
user data is 4428
[ATTRIBUTE] handle 217
uuid type = 0, val=2803
UID: 9a66fb18-0800-9191-11e4-012d1540cb8e
attr is a characteristic.  UUID type is 2, val = 40cb
UID: 31000000-0020-0021-4820-0019f828032c
attr is a CCCD.  UUID type is 0, val = 2803
user data is 4428
[UNSUBSCRIBED]
[NOTIFICATION] data (nil) length 0
[ATTRIBUTE] handle 220
uuid type = 0, val=2803
UID: 9a66fb19-0800-9191-11e4-012d1540cb8e
attr is a characteristic.  UUID type is 2, val = 40cb
UID: 31000000-0020-0021-4820-0019f82803a1
attr is a CCCD.  UUID type is 0, val = 2803
user data is 4428
[ATTRIBUTE] handle 223
uuid type = 0, val=2803
UID: 9a66fb1a-0800-9191-11e4-012d1540cb8e
attr is a characteristic.  UUID type is 2, val = 40cb
UID: 31000000-0020-0021-4820-0019f82803a1
attr is a CCCD.  UUID type is 0, val = 2803
user data is 4428
[ATTRIBUTE] handle 226
uuid type = 0, val=2803
UID: 9a66fb1b-0800-9191-11e4-012d1540cb8e
attr is a characteristic.  UUID type is 2, val = 40cb
[00:00:24.004,821] <dbg> central_gatt: discover_services: FOUND DRONE TX ACKACK FB1B


[00:00:24.005,310] <dbg> central_gatt: discover_services: tx1b handle: 226 
[SUBSCRIBED ACK ACK 1B]
UID: 31000000-0020-0021-4820-0019f82803a1
attr is a CCCD.  UUID type is 0, val = 2803
user data is 4428
[ATTRIBUTE] handle 229
uuid type = 0, val=2803
UID: 9a66fb1c-0800-9191-11e4-012d1540cb8e
attr is a characteristic.  UUID type is 2, val = 40cb
[00:00:24.008,392] <dbg> central_gatt: discover_services: FOUND DRONE TX HIPRI FB1C


[00:00:24.008,911] <dbg> central_gatt: discover_services: tx1c handle: 229 
[SUBSCRIBED HIPRI 1C]
UID: 31000000-0020-0021-4820-0019f82803a1
attr is a CCCD.  UUID type is 0, val = 2803
user data is 4428
[ATTRIBUTE] handle 232
uuid type = 0, val=2803
UID: 9a66fb1d-0800-9191-11e4-012d1540cb8e
attr is a characteristic.  UUID type is 2, val = 40cb
UID: 31000000-0020-0021-4820-0019f82803a1
attr is a CCCD.  UUID type is 0, val = 2803
user data is 4428
[ATTRIBUTE] handle 235
uuid type = 0, val=2803
UID: 9a66fb1e-0800-9191-11e4-012d1540cb8e
attr is a characteristic.  UUID type is 2, val = 40cb
UID: 31000000-0020-0021-4820-0019f82803a1
attr is a CCCD.  UUID type is 0, val = 2803
user data is 4428
[ATTRIBUTE] handle 238
uuid type = 0, val=2803
UID: 9a66fb1f-0800-9191-11e4-012d1540cb8e
attr is a characteristic.  UUID type is 2, val = 40cb
UID: 31000000-0020-0021-4820-0019f82803a1
attr is a CCCD.  UUID type is 0, val = 2803
user data is 4428
[ATTRIBUTE] handle 273
uuid type = 0, val=2803
UID: 9a66fd22-0800-9191-11e4-012d1540cb8e
attr is a characteristic.  UUID type is 2, val = 40cb
UID: 31000000-0020-0021-4820-0019f82803a1
attr is a CCCD.  UUID type is 0, val = 2803
user data is 4428
[ATTRIBUTE] handle 276
uuid type = 0, val=2803
UID: 9a66fd23-0800-9191-11e4-012d1540cb8e
attr is a characteristic.  UUID type is 2, val = 40cb
UID: 31000000-0020-0021-4820-0019f82803a1
attr is a CCCD.  UUID type is 0, val = 2803
user data is 4428
[ATTRIBUTE] handle 279
uuid type = 0, val=2803
UID: 9a66fd24-0800-9191-11e4-012d1540cb8e
attr is a characteristic.  UUID type is 2, val = 40cb
UID: 31000000-0020-0021-4820-0019f82803a1
attr is a CCCD.  UUID type is 0, val = 2803
user data is 4428
[ATTRIBUTE] handle 289
uuid type = 0, val=2803
UID: 9a66fd52-0800-9191-11e4-012d1540cb8e
attr is a characteristic.  UUID type is 2, val = 40cb
UID: 31000000-0020-0021-4820-0019f82803a1
attr is a CCCD.  UUID type is 0, val = 2803
user data is 4428
[UNSUBSCRIBED]
[NOTIFICATION] data (nil) length 0
[ATTRIBUTE] handle 292
uuid type = 0, val=2803
UID: 9a66fd53-0800-9191-11e4-012d1540cb8e
attr is a characteristic.  UUID type is 2, val = 40cb
UID: 31000000-0020-0021-4820-0019f82803a1
attr is a CCCD.  UUID type is 0, val = 2803
user data is 4428
[ATTRIBUTE] handle 295
uuid type = 0, val=2803
UID: 9a66fd54-0800-9191-11e4-012d1540cb8e
attr is a characteristic.  UUID type is 2, val = 40cb
UID: 31000000-0020-0021-4820-0019f82803a1
attr is a CCCD.  UUID type is 0, val = 2803
user data is 4428
[ATTRIBUTE] handle 305
uuid type = 0, val=2803
UID: 9a66fe01-0800-9191-11e4-012d1540cb8e
attr is a characteristic.  UUID type is 2, val = 40cb
UID: 31000000-0020-0021-4820-0019f82803a1
attr is a CCCD.  UUID type is 0, val = 2803
user data is 4428
[ATTRIBUTE] handle 308
uuid type = 0, val=2803
UID: 9a66fe02-0800-9191-11e4-012d1540cb8e
attr is a characteristic.  UUID type is 2, val = 40cb
UID: 31000000-0020-0021-4820-0019f82803a1
attr is a CCCD.  UUID type is 0, val = 2803
user data is 4428
No more characteristics, looking for CCCDs
[ATTRIBUTE] handle 309
uuid type = 2, val=40cb
UID: 9a66fe02-0800-9191-11e4-012d1540cb8e
attr is a CCCD.  UUID type is 2, val = 40cb
user_data is NULL
[ATTRIBUTE] handle 310
uuid type = 0, val=2902
UID: 9a66fe02-0800-9191-11e4-012d1529028e
attr is a CCCD.  UUID type is 0, val = 2902
user_data is NULL
Discovery complete
[00:00:52.002,410] <dbg> central_gatt: central_gatt_write: Calling write
[00:00:52.002,899] <dbg> gatt_common: write_cmd: sending data to 63
[00:00:52.003,448] <dbg> gatt_common: write_cmd: data sent
[00:01:22.003,936] <dbg> central_gatt: central_gatt_write: Calling write
[00:01:22.004,425] <dbg> gatt_common: write_cmd: sending data to 63
[00:01:22.004,974] <dbg> gatt_common: write_cmd: data sent

 Unfortunately I've never been able to get the Wireshark Nrf sniffer to work and don't currently have another sniffer available.  I'm working on getting one now.

Please let me know if I've done something wrong in the ode above.

Brian

[Edvin]

Hello Brian,

I am sorry, but these snippets confuse me. Is it possible to zip and send two applications, one peripheral and one central that I can use to replicate what you are seeing?

I need to be able to run them on 2 DKs.

Usually when we get questions about the discovery procedure, I just reference the samples, such as the peripheral_uart and central_uart samples. I suggest you use the bt_gatt_dm_start() instead of bt_gatt_discover() directly, and you don't need to handle the state machine (BT_GATT_ITER_CONTINUE and BT_GATT_ITER_STOP) 

If you for some reason need to use bt_gatt_discover() directly, it should be fine. It is what bt_gatt_dm_start() does. But in that case, I suggest you look at the implementation of bt_gatt_dm_start() in gatt_dm.c, and implement something similiar.  This one handles the return values (BT_GATT_ITER_CONTINUE and BT_GATT_ITER_STOP).

It looks like BT_GATT_ITER_CONTINUE should be returned when there are more services/characteristics to discover. BT_GATT_ITER_STOP should be used when you are either done, or if you run into an error.

But I think you should investigate using bt_gatt_dm_start(), where you set the svc_uuid to NULL to discover all services. Then you call bt_gatt_dm_continue() to discover the next service when you are done handling one in the discovery_completed event.

Best regards,

Edvin

[finkbr]

Hi,

1) Cant send you code for the peripherial since i dont have it, it was existing firmware i need to connect to and use.  

2) Seems like the usual answer from support, look at the central UART app, its seems like support doesn't think we research anything.  I've looked at it, I'm new to this, it doesn't really apply since I'm not using a UART and the device I'm connecting to doesn't have a UART for me to connect to to even try.  The 52dk board does and I can load it and it works. now what, the 52dk board doesn't connect to the peripheral I'm trying to scan.  The NRF connect app connects, scans and lists ALL of the services and characteristics and i can send and receive data using that BUT code isn't available for that app to see how it works.

3) if you can look earlier in this ticket, you'll see that i said i tried the bt_gatt_dm_start but i get an error that there is not enough memory.  i found a post that said to increase 

CONFIG_BT_GATT_DM_MAX_ATTRS=

I increased that to 350 since i have so many characteristics.  still fails.  couldnt get any further using that.  This was in the initial post.

I'll look at the implementation of gatt_dm and maybe ill be able to figure this out.  The documentation is severely lacking and doesn't explain much.

I am at the point now, where i have been able to discover the services and characteristics but while trying to write, nothing happens.  i saved the handle for the characteristic i wanted to write to (63) and tried a write without response.  data is not getting sent from what i can tell.  If you have any ideas about that, please let em know.

[Edvin]

Brian, 

Obviously, I am not saying that you should use the central UART application in your final device. What I meant to say was that you could look into how the central_uart application is handling the discovery procedure. That is not an unusual request from support. 

The reason I asked you to do this is that you started asking about BT_GATT_ITER_CONTINUE and BT_GATT_ITER_STOP, which are two return values I have never noticed before. This means that they are handled by the bt_gatt_dm module, which is why I never needed to look into them. Therefore, i thought it could be a good idea to use that, as this module seems a lot more comprehendible than implementing the state machine used in bt_gatt_discover(). 

finkbr said:

3) if you can look earlier in this ticket, you'll see that i said i tried the bt_gatt_dm_start but i get an error that there is not enough memory.  i found a post that said to increase 

CONFIG_BT_GATT_DM_MAX_ATTRS=

I increased that to 350 since i have so many characteristics.  still fails.  couldnt get any further using that.

So chan you please let me know what makes you think you don't have enough memory? Please note that I do believe that it says so, but I need to know where it says. From what function? Is this printed in the log? Where? 

You said that you increased CONFIG_BT_GATT_DM_MAX_ATTRS to 350. Did that change anything? Were you able to discover more characteristics than the default CONFIG_BT_GATT_DM_MAX_ATTRS=35 (which is the default value)?

Is it the log from gatt_dm.c line 299 (NCSv2.3.0)

LOG_ERR("Not enough memory for service attribute.");

that you are seeing in your log?

If so, can you please clarify whether you found more services/characteristics when increeading the CONFIG_BT_GATT_DM_MAX_ATTRS=350?

Can you confirm that your CONFIG_BT_GATT_DM_MAX_ATTRS is actually increased when you build? If you are using the 52 series (nRF52832), then this should be visible in your build folder:

build\zephyr\include\generated\autoconf.h

In there you should see all the definitions that ends up in your build. If some conditions do not apply for a config, it may default back to the default value even if you tried to change it in prj.conf.

Best regards,

Edvin

[finkbr]

yes that is the error i am seeing.  i can see that it is indeed increased to 350 and i can also verify that no more characteristics have been found.