BtBls.c

// GATT Battery Service
// MZachmann 2020
// MIT License

// this is the gatt standard battery level indicator
// it may send a notification when the battery level is set
#include <bluetooth/bluetooth.h>
#include <bluetooth/conn.h>
#include <bluetooth/gatt.h>
#include <bluetooth/uuid.h>
#include <logging/log.h>
LOG_MODULE_REGISTER(BtBls, LOG_LEVEL_INF);

// persistant characteristic data
static u8_t _BatteryLevel = 100U;
static bool _IsTxEnabled = false;

// notification changed callback, log it
static void NotifyEnabledCb(const struct bt_gatt_attr *attr, u16_t value)
{
	ARG_UNUSED(attr);
	_IsTxEnabled = (value == BT_GATT_CCC_NOTIFY);
	LOG_INF("Battery level notification %s.", _IsTxEnabled ? "enabled" : "disabled");
}

// attribute read callback
static ssize_t ReadBlvlCb(struct bt_conn *conn,
			       const struct bt_gatt_attr *attr, void *buf,
			       u16_t len, u16_t offset)
{
	u8_t lvl8 = _BatteryLevel;
	return bt_gatt_attr_read(conn, attr, buf, len, offset, &lvl8, sizeof(lvl8));
}

// the heavy lifter that defines the service completely
BT_GATT_SERVICE_DEFINE(_BlsService,
	BT_GATT_PRIMARY_SERVICE(BT_UUID_BAS),
	BT_GATT_CHARACTERISTIC(BT_UUID_BAS_BATTERY_LEVEL,
			       BT_GATT_CHRC_READ | BT_GATT_CHRC_NOTIFY,
			       BT_GATT_PERM_READ, ReadBlvlCb, NULL,
			       &_BatteryLevel),
	BT_GATT_CCC(NotifyEnabledCb,
		    BT_GATT_PERM_READ | BT_GATT_PERM_WRITE),
);

// ------------------------------------------------------------
// user-callable method to set the battery level in the service
// ------------------------------------------------------------
int BtSetBattery(u8_t level)
{
	if(! _IsTxEnabled)
		return -ENOEXEC;
	if (level > 100U) 
		return -EINVAL;

	_BatteryLevel = level;	// the persistant value is used by the gatt reader
	int rc = bt_gatt_notify(NULL, &_BlsService.attrs[1], &level, sizeof(level));
	return (rc == -ENOTCONN) ? 0 : rc;
}