Private GATT NOTIFY

RE: Private GATT NOTIFY

MtnDrew — Tue, 14 Nov 2023 21:44:49 GMT

Yes!! This allows me to define an attrs struct:

static struct bt_gatt_attr svc_attrs[] = {{&data_uuid.uuid}};
static struct bt_gatt_service logAttrs;

Then in main:

logAttrs = (struct bt_gatt_service)BT_GATT_SERVICE(svc_attrs);

In my notify function:

err = bt_gatt_notify_uuid(NULL, &data_uuid.uuid, logAttrs.attrs, &logData, sizeof(logData));

And I'm able to eliminate the write property from my characteristic:

	BT_GATT_CHARACTERISTIC(&data_uuid.uuid,
		BT_GATT_CHRC_NOTIFY, 
		BT_GATT_PERM_READ, NULL, NULL, NULL),
	BT_GATT_CCC(data_ccc_cfg_changed, BT_GATT_PERM_READ | BT_GATT_PERM_WRITE),

Thank you, Amanda for your guidance. If you see any glaring errors in my implementation above, I welcome your suggestions. Otherwise you may consider this matter solved.

Drew

RE: Private GATT NOTIFY

Amanda Hsieh — Mon, 13 Nov 2023 20:37:50 GMT

Hi,

-128 is ENOTCONN which means the socket is not connected and is returned by bt_gatt_notify_cb in the bt_gatt_notify_uuid(). It needs to check the connection status.

If you create a GATT Service with bt_gatt_service, you could use .attrs.
See the example:
https://github.com/nrfconnect/sdk-zephyr/blob/v3.4.99-ncs1/subsys/bluetooth/audio/mcs.c#L914
https://github.com/nrfconnect/sdk-zephyr/blob/v3.4.99-ncs1/subsys/bluetooth/audio/mcs.c#L932

Regards,
Amanda H.

RE: Private GATT NOTIFY

MtnDrew — Fri, 10 Nov 2023 16:30:28 GMT

As coded above the bt_gatt_notify_uuid() function returns "-128". I also receive a LOG_WRN message "Link is not encrypted".

As A workaround, this is how I've had to define the characteristic:

    BT_GATT_CHARACTERISTIC(&data_uuid.uuid,
        BT_GATT_CHRC_NOTIFY | BT_GATT_CHRC_READ,
        BT_GATT_PERM_READ, read_data, NULL, NULL),
	BT_GATT_CCC(data_ccc_cfg_changed, BT_GATT_PERM_READ | BT_GATT_PERM_WRITE),

Then I declare a bt_gatt_attr in global scope:

struct bt_gatt_attr *privateAttr;

And assign it to the attr passed into the read callback:

static ssize_t read_data(

    struct bt_conn *conn,
    const struct bt_gatt_attr *attr,
    void *buf, uint16_t len, uint16_t offset)
{

	privateAttr = attr; // TODO: Acquire attribute
		
	uint8_t logData[10];

	getLogData((uint8_t*)&logData);

    return bt_gatt_attr_read(conn, attr, buf, len, offset, &logData, sizeof(logData));
}

And that is used in my bt_gatt_notify_uuid() call:

uint8_t data_notify(void) 
{
	//LOG_INF("Data Notification");

	int err;

	uint8_t logData[10];

	getLogData((uint8_t*)&logData);

	err = bt_gatt_notify_uuid(NULL, &data_uuid.uuid, privateAttr, &logData, sizeof(logData));
	if(err) {

		LOG_DBG("Data Notify Error = %d", err);
		return err;
	}

	return 1;
}

This works but it is a bit of a hack as our customer only required a NOTIFY property on this characteristic.

Again, I believe the issue might be in how I am acquiring the "attr" parameter from the bt_gatt_notify_uuid() call.

Any suggestions would be appreciated.

-Drew

RE: Private GATT NOTIFY

khelmutlord — Thu, 09 Nov 2023 20:19:55 GMT

Hello Drew,

Could you share what return value you receive from your call to bt_gatt_notify_uuid?

Thanks,

Helmut Lord