How to change the data length of BLE notification

[diode]

The maximum data length of a characteristic is 9, and I use the follow function to send the notification to a client

uint32_t dxs_send(dr_ble_dxs_t * p_dxs, uint8_t * p_data, uint16_t length)
{
	uint32_t ret_code;
	
	ble_gatts_hvx_params_t hvx_params;
	
	if (p_dxs == NULL)
	{
			return NRF_ERROR_NULL;
	}

	if ((p_dxs->conn_handle == BLE_CONN_HANDLE_INVALID) || (!p_dxs->is_notification_enabled_ctrl))
	{
			return NRF_ERROR_INVALID_STATE;
	}

	memset(&hvx_params, 0, sizeof(hvx_params));

	hvx_params.handle = p_dxs->ctrl_handles.value_handle;
	hvx_params.p_data = p_data;
	hvx_params.p_len  = &length;
	hvx_params.type   = BLE_GATT_HVX_NOTIFICATION;
	
	ret_code = sd_ble_gatts_hvx(p_dxs->conn_handle, &hvx_params);
	
	return ret_code;
}

The problem is I always get notification with length of 9 on the client side, even though the input argument "length" is smaller than 9. Is there a way to change the length of notification data?

[shibshab]

In ATT, an attribute can have either fixed or variable length. This implies that the client you are sending notifications to need to have configured the characteristic value attribute with variable length.

When you create the characteristic of which you are sending the value, make sure you set the property Variable Length to 1.

[Stefan Birnir Sverrisson]

Hi

I want to provide basically the same answer as shibshab provided, with little more specifics. This is how the length parameters are presented in the BLE examples in the nRF51 SDK:

attr.max_len

attr.init_len

attr_md.vlen

which define the maximum length for the characteristic, initial length, and if the characteristic should have variable length or not. Modify these three as needed.