How to read local attribute value in BLE peripheral

[quan1328]

Hi,

I am making an application on nRF52840 (SDK 2.2.0) as a BLE peripheral.

When something happens at this peripheral, the application will notify a value to the connected manager.

Below mycode.c:

 

void chrc_ccc_cfg_changed(const struct bt_gatt_attr *attr, uint16_t value)
{
LOG_INF("value: %d", value);
bool notif_enabled = (value == BT_GATT_CCC_NOTIFY);
LOG_INF("Notification: %s", notif_enabled ? "enabled" : "disabled");
LOG_INF("Perm: %d", attr->perm);

bt_gatt_service_val val = btgatservice
}

BT_GATT_SERVICE_DEFINE(remote_srv,
BT_GATT_PRIMARY_SERVICE(BT_UUID_REMOTE_SERVICE),
BT_GATT_CHARACTERISTIC(BT_UUID_REMOTE_BUTTON_CHAR,
BT_GATT_CHRC_READ | BT_GATT_CHRC_NOTIFY,
BT_GATT_PERM_READ,
read_characteristic_cb, NULL, NULL),
BT_GATT_CCC(chrc_ccc_cfg_changed, BT_GATT_PERM_READ | BT_GATT_PERM_WRITE),
BT_GATT_CHARACTERISTIC(BT_UUID_REMOTE_MESSAGE_CHAR,
BT_GATT_CHRC_WRITE_WITHOUT_RESP,
BT_GATT_PERM_READ | BT_GATT_PERM_WRITE, NULL, on_written, NULL));

void notify_value(uint8_t value)
{
struct bt_gatt_notify_params params =
{
.attr = &remote_srv.attrs[2],
.data = &value,
.len = sizeof(value),
.func = on_notified,
};

bt_gatt_attr_read()

// ! read the attribute value before sending, to make sure no `err`
int err = bt_gatt_notify_cb(current_conn, &params);


button_value = value;
}

Everything works fine.

Now, in `notify_value()`, before `bt_gatt_notify_cb()`, I want to read the attribute value before notifying. This is to make sure I only notify when the attribute's notification is enabled.

How should I do that?

Regards,

[Vidar Berg]

Hi,

You should be able to use bt_gatt_attr_read_ccc() to read the current CCCD configuration from the local database. But would it not be easier to just read the return code from bt_gatt_notify_cb() to determine if the notification got sent or not?

Best regards,

Vidar

[quan1328]

Thanks for your answer.

Yes, I did think about your solution, but hesitate because if I could read a local attribute of a characteristic using the API, it would save me a global variable of taking the returned value from `bt_gatt_notify_cb()`.