# Bluetooth Low Energy library
**Important**
This library is hosted on the Amazon-FreeRTOS repository which is deprecated. We recommend that you [start here](freertos-getting-started-modular.md) when you create a new project. If you already have an existing FreeRTOS project based on the now deprecated Amazon-FreeRTOS repository, see the [Amazon-FreeRTOS Github Repository Migration Guide](github-repo-migration.md).
## Overview
FreeRTOS supports publishing and subscribing to Message Queuing Telemetry Transport (MQTT) topics over Bluetooth Low Energy through a proxy device, such as a mobile phone. With the FreeRTOS [Bluetooth Low Energy](https://docs.aws.amazon.com/freertos/latest/lib-ref/html2/ble/index.html) (BLE) library, your microcontroller can securely communicate with the AWS IoT MQTT broker.
![\[BLE devices connecting to AWS IoT Core via MQTT/HTTP/Websocket through AWS Cognito.\]](http://docs.aws.amazon.com/freertos/latest/userguide/images/blediagram.jpg)
Using the Mobile SDKs for FreeRTOS Bluetooth Devices, you can write native mobile applications that communicate with the embedded applications on your microcontroller over BLE. For more information about the mobile SDKs, see [Mobile SDKs for FreeRTOS Bluetooth devices](freertos-ble-mobile.md).
The FreeRTOS BLE library includes services for configuring Wi-Fi networks, transferring large amounts of data, and providing network abstractions over BLE. The FreeRTOS BLE library also includes middleware and lower-level APIs for more direct control over your BLE stack.
## Architecture
Three layers make up the FreeRTOS BLE library: services, middleware, and low-level wrappers.
![\[Cloud architecture layers: User Application, Services, Middleware, Low-level Wrappers, Manufacturer BLE Stack.\]](http://docs.aws.amazon.com/freertos/latest/userguide/images/ble-architecture.png)
### Services
The FreeRTOS BLE services layer consists of four Generic Attribute (GATT) services that leverage the middleware APIs:
+ Device information
+ Wi-Fi provisioning
+ Network abstraction
+ Large object transfer
#### Device information
The Device information service gathers details about your microcontroller, including:
+ The version of FreeRTOS that your device is using.
+ The AWS IoT endpoint of the account for which the device is registered.
+ Bluetooth Low Energy Maximum Transmission Unit (MTU).
#### Wi-Fi provisioning
The Wi-Fi provisioning service enables microcontrollers with Wi-Fi capabilities to do the following:
+ List networks in range.
+ Save networks and network credentials to flash memory.
+ Set network priority.
+ Delete networks and network credentials from flash memory.
#### Network abstraction
The network abstraction service abstracts the network connection type for applications. A common API interacts with your device's Wi-Fi, Ethernet, and Bluetooth Low Energy hardware stack, enabling an application to be compatible with multiple connection types.
#### Large Object Transfer
The Large Object Transfer service sends data to, and receives data from, a client. Other services, like Wi-Fi provisioning and Network abstraction, use the Large Object Transfer service to send and receive data. You can also use the Large Object Transfer API to directly interact with the service.
#### MQTT over BLE
MQTT over BLE contains the GATT profile for creating an MQTT proxy service over BLE. The MQTT proxy service allows an MQTT client to communicate with the AWS MQTT broker through a gateway device. For example, you can use the proxy service to connect a device running FreeRTOS to AWS MQTT through a smartphone app. The BLE device is the GATT server and exposes services and characteristics for the gateway device. The GATT server uses these exposed services and characteristics to perform MQTT operations with the cloud for that device. For more details, refer to [Appendix A: MQTT over BLE GATT profile](#freertos-ble-gatt-profile).
### Middleware
FreeRTOS Bluetooth Low Energy middleware is an abstraction from the lower-level APIs. The middleware APIs make up a more user-friendly interface to the Bluetooth Low Energy stack.
Using middleware APIs, you can register several callbacks, across multiple layers, to a single event. Initializing the Bluetooth Low Energy middleware also initializes services and starts advertising.
#### Flexible callback subscription
Suppose your Bluetooth Low Energy hardware disconnects, and the MQTT over Bluetooth Low Energy service needs to detect the disconnection. An application that you wrote might also need to detect the same disconnection event. The Bluetooth Low Energy middleware can route the event to different parts of the code where you have registered callbacks, without making the higher layers compete for lower-level resources.
### Low-level wrappers
The low-level FreeRTOS Bluetooth Low Energy wrappers are an abstraction from the manufacturer's Bluetooth Low Energy stack. Low-level wrappers offer a common set of APIs for direct control over the hardware. The low-level APIs optimize RAM usage, but are limited in functionality.
Use the Bluetooth Low Energy service APIs to interact with the Bluetooth Low Energy services. The service APIs demand more resources than the low-level APIs.
## Dependencies and requirements
The Bluetooth Low Energy library has the following direct dependencies:
+ [Linear Containers](https://docs.aws.amazon.com/freertos/latest/lib-ref/c-sdk/linear_containers/index.html) library
+ A platform layer that interfaces with the operating system for thread management, timers, clock functions, and network access.
![\[Architecture diagram showing components: BLE, List/Queue, Network, and Clock, with directional arrows indicating interactions.\]](http://docs.aws.amazon.com/freertos/latest/userguide/images/ble-dependencies.png)
Only the Wi-Fi Provisioning service has FreeRTOS library dependencies:
****
| GATT Service | Dependency |
| --- | --- |
| Wi-Fi Provisioning | [Wi-Fi library](freertos-wifi.md) |
To communicate with the AWS IoT MQTT broker, you must have an AWS account and you must register your devices as AWS IoT things. For more information about setting up, see the [AWS IoT Developer Guide](https://docs.aws.amazon.com/iot/latest/developerguide/).
FreeRTOS Bluetooth Low Energy uses Amazon Cognito for user authentication on your mobile device. To use MQTT proxy services, you must create an Amazon Cognito identity and user pools. Each Amazon Cognito Identity must have the appropriate policy attached to it. For more information, see the [Amazon Cognito Developer Guide](https://docs.aws.amazon.com/cognito/latest/developerguide/).
## Library configuration file
Applications that use the FreeRTOS MQTT over Bluetooth Low Energy service must provide an `iot_ble_config.h` header file, in which configuration parameters are defined. Undefined configuration parameters take the default values specified in `iot_ble_config_defaults.h`.
Some important configuration parameters include:
**`IOT_BLE_ADD_CUSTOM_SERVICES`**
Allows users to create their own services.
**`IOT_BLE_SET_CUSTOM_ADVERTISEMENT_MSG`**
Allows users to customize the advertisement and scan response messages.
For more information, see [Bluetooth Low Energy API Reference](https://docs.aws.amazon.com/freertos/latest/lib-ref/html2/ble/index.html).
## Optimization
When optimizing your board's performance, consider the following:
+ Low-level APIs use less RAM, but offer limited functionality.
+ You can set the `bleconfigMAX_NETWORK` parameter in the `iot_ble_config.h` header file to a lower value to reduce the amount of stack consumed.
+ You can increase the MTU size to its maximum value to limit message buffering, and make code run faster and consume less RAM.
## Usage restrictions
By default, the FreeRTOS Bluetooth Low Energy library sets the `eBTpropertySecureConnectionOnly` property to TRUE, which places the device in a Secure Connections Only mode. As specified by the [Bluetooth Core Specification](https://www.bluetooth.com/specifications/bluetooth-core-specification) v5.0, Vol 3, Part C, 10.2.4, when a device is in a Secure Connections Only mode, the highest LE security mode 1 level, level 4, is required for access to any attribute that has permissions higher than the lowest LE security mode 1 level, level 1. At the LE security mode 1 level 4, a device must have input and output capabilities for numeric comparison.
Here are the supported modes, and their associated properties:
**Mode 1, Level 1 (No security)**
```
/* Disable numeric comparison */
#define IOT_BLE_ENABLE_NUMERIC_COMPARISON ( 0 )
#define IOT_BLE_ENABLE_SECURE_CONNECTION ( 0 )
#define IOT_BLE_INPUT_OUTPUT ( eBTIONone )
#define IOT_BLE_ENCRYPTION_REQUIRED ( 0 )
```
**Mode 1, Level 2 (Unauthenticated pairing with encryption)**
```
#define IOT_BLE_ENABLE_NUMERIC_COMPARISON ( 0 )
#define IOT_BLE_ENABLE_SECURE_CONNECTION ( 0 )
#define IOT_BLE_INPUT_OUTPUT ( eBTIONone )
```
**Mode 1, Level 3 (Authenticated pairing with encryption)**
This mode is not supported.
**Mode 1, Level 4 (Authenticated LE Secure Connections pairing with encryption)**
This mode is supported by default.
For information about LE security modes, see the [Bluetooth Core Specification](https://www.bluetooth.com/specifications/bluetooth-core-specification) v5.0, Vol 3, Part C, 10.2.1.
## Initialization
If your application interacts with the Bluetooth Low Energy stack through middleware, you only need to initialize the middleware. Middleware takes care of initializing the lower layers of the stack.
### Middleware
**To initialize the middleware**
1. Initialize any Bluetooth Low Energy hardware drivers before you call the Bluetooth Low Energy middleware API.
1. Enable Bluetooth Low Energy.
1. Initialize the middleware with `IotBLE_Init()`.
**Note**
This initialization step is not required if you are running the AWS demos. Demo initialization is handled by the Network Manager, located at `freertos/demos/network_manager`.
### Low-level APIs
If you don't want to use the FreeRTOS Bluetooth Low Energy GATT services, you can bypass the middleware and interact directly with the low-level APIs to save resources.
**To initialize the low-level APIs**
1.
****
Initialize any Bluetooth Low Energy hardware drivers before you call the APIs. Driver initialization is not part of the Bluetooth Low Energy low-level APIs.
1.
****
The Bluetooth Low Energy low-level API provides an enable/disable call to the Bluetooth Low Energy stack for optimizing power and resources. Before calling the APIs, you must enable Bluetooth Low Energy.
```
const BTInterface_t * pxIface = BTGetBluetoothInterface();
xStatus = pxIface->pxEnable( 0 );
```
1.
****
The Bluetooth manager contains APIs that are common to both Bluetooth Low Energy and Bluetooth classic. The callbacks for the common manager must be initialized second.
```
xStatus = xBTInterface.pxBTInterface->pxBtManagerInit( &xBTManagerCb );
```
1.
****
The Bluetooth Low Energy adapter fits on top of the common API. You must initialize its callbacks like you initialized the common API.
```
xBTInterface.pxBTLeAdapterInterface = ( BTBleAdapter_t * ) xBTInterface.pxBTInterface->pxGetLeAdapter();
xStatus = xBTInterface.pxBTLeAdapterInterface->pxBleAdapterInit( &xBTBleAdapterCb );
```
1.
****
Register your new user application.
```
xBTInterface.pxBTLeAdapterInterface->pxRegisterBleApp( pxAppUuid );
```
1.
****
Initialize the callbacks to the GATT servers.
```
xBTInterface.pxGattServerInterface = ( BTGattServerInterface_t * ) xBTInterface.pxBTLeAdapterInterface->ppvGetGattServerInterface();
xBTInterface.pxGattServerInterface->pxGattServerInit( &xBTGattServerCb );
```
After you initialize the Bluetooth Low Energy adapter, you can add a GATT server. You can register only one GATT server at a time.
```
xStatus = xBTInterface.pxGattServerInterface->pxRegisterServer( pxAppUuid );
```
1.
****
Set application properties like secure connection only and MTU size.
```
xStatus = xBTInterface.pxBTInterface->pxSetDeviceProperty( &pxProperty[ usIndex ] );
```
## API reference
For a full API reference, see [Bluetooth Low Energy API Reference](https://docs.aws.amazon.com/freertos/latest/lib-ref/html2/ble/index.html).
## Example usage
The examples below demonstrate how to use the Bluetooth Low Energy library for advertising and creating new services. For full FreeRTOS Bluetooth Low Energy demo applications, see [Bluetooth Low Energy Demo Applications](https://docs.aws.amazon.com/freertos/latest/userguide/ble-demo.html).
### Advertising
1. In your application, set the advertising UUID:
```
static const BTUuid_t _advUUID =
{
.uu.uu128 = IOT_BLE_ADVERTISING_UUID,
.ucType = eBTuuidType128
};
```
1. Then define the `IotBle_SetCustomAdvCb` callback function:
```
void IotBle_SetCustomAdvCb( IotBleAdvertisementParams_t * pAdvParams, IotBleAdvertisementParams_t * pScanParams)
{
memset(pAdvParams, 0, sizeof(IotBleAdvertisementParams_t));
memset(pScanParams, 0, sizeof(IotBleAdvertisementParams_t));
/* Set advertisement message */
pAdvParams->pUUID1 = &_advUUID;
pAdvParams->nameType = BTGattAdvNameNone;
/* This is the scan response, set it back to true. */
pScanParams->setScanRsp = true;
pScanParams->nameType = BTGattAdvNameComplete;
}
```
This callback sends the UUID in the advertisement message and the full name in the scan response.
1. Open `vendors/vendor/boards/board/aws_demos/config_files/iot_ble_config.h`, and set `IOT_BLE_SET_CUSTOM_ADVERTISEMENT_MSG` to `1`. This triggers the `IotBle_SetCustomAdvCb` callback.
### Adding a new service
For full examples of services, see `freertos/.../ble/services`.
1. Create UUIDs for the service's characteristic and descriptors:
```
#define xServiceUUID_TYPE \
{\
.uu.uu128 = gattDemoSVC_UUID, \
.ucType = eBTuuidType128 \
}
#define xCharCounterUUID_TYPE \
{\
.uu.uu128 = gattDemoCHAR_COUNTER_UUID,\
.ucType = eBTuuidType128\
}
#define xCharControlUUID_TYPE \
{\
.uu.uu128 = gattDemoCHAR_CONTROL_UUID,\
.ucType = eBTuuidType128\
}
#define xClientCharCfgUUID_TYPE \
{\
.uu.uu16 = gattDemoCLIENT_CHAR_CFG_UUID,\
.ucType = eBTuuidType16\
}
```
1. Create a buffer to register the handles of the characteristic and descriptors:
```
static uint16_t usHandlesBuffer[egattDemoNbAttributes];
```
1. Create the attribute table. To save some RAM, define the table as a `const`.
**Important**
Always create the attributes in order, with the service as the first attribute.
```
static const BTAttribute_t pxAttributeTable[] = {
{
.xServiceUUID = xServiceUUID_TYPE
},
{
.xAttributeType = eBTDbCharacteristic,
.xCharacteristic =
{
.xUuid = xCharCounterUUID_TYPE,
.xPermissions = ( IOT_BLE_CHAR_READ_PERM ),
.xProperties = ( eBTPropRead | eBTPropNotify )
}
},
{
.xAttributeType = eBTDbDescriptor,
.xCharacteristicDescr =
{
.xUuid = xClientCharCfgUUID_TYPE,
.xPermissions = ( IOT_BLE_CHAR_READ_PERM | IOT_BLE_CHAR_WRITE_PERM )
}
},
{
.xAttributeType = eBTDbCharacteristic,
.xCharacteristic =
{
.xUuid = xCharControlUUID_TYPE,
.xPermissions = ( IOT_BLE_CHAR_READ_PERM | IOT_BLE_CHAR_WRITE_PERM ),
.xProperties = ( eBTPropRead | eBTPropWrite )
}
}
};
```
1. Create an array of callbacks. This array of callbacks must follow the same order as the table array defined above.
For example, if `vReadCounter` gets triggered when `xCharCounterUUID_TYPE` is accessed, and `vWriteCommand` gets triggered when `xCharControlUUID_TYPE` is accessed, define the array as follows:
```
static const IotBleAttributeEventCallback_t pxCallBackArray[egattDemoNbAttributes] =
{
NULL,
vReadCounter,
vEnableNotification,
vWriteCommand
};
```
1. Create the service:
```
static const BTService_t xGattDemoService =
{
.xNumberOfAttributes = egattDemoNbAttributes,
.ucInstId = 0,
.xType = eBTServiceTypePrimary,
.pusHandlesBuffer = usHandlesBuffer,
.pxBLEAttributes = (BTAttribute_t *)pxAttributeTable
};
```
1. Call the API `IotBle_CreateService` with the structure that you created in the previous step. The middleware synchronizes the creation of all services, so any new services need to already be defined when the `IotBle_AddCustomServicesCb` callback is triggered.
1. Set `IOT_BLE_ADD_CUSTOM_SERVICES` to `1` in `vendors/vendor/boards/board/aws_demos/config_files/iot_ble_config.h`.
1. Create IotBle\$1AddCustomServicesCb in your application:
```
void IotBle_AddCustomServicesCb(void)
{
BTStatus_t xStatus;
/* Select the handle buffer. */
xStatus = IotBle_CreateService( (BTService_t *)&xGattDemoService, (IotBleAttributeEventCallback_t *)pxCallBackArray );
}
```
## Porting
### User input and output peripheral
A secure connection requires both input and output for numeric comparison. The `eBLENumericComparisonCallback` event can be registered using the event manager:
```
xEventCb.pxNumericComparisonCb = &prvNumericComparisonCb;
xStatus = BLE_RegisterEventCb( eBLENumericComparisonCallback, xEventCb );
```
The peripheral must display the numeric passkey and take the result of the comparison as an input.
### Porting API implementations
To port FreeRTOS to a new target, you must implement some APIs for the Wi-Fi Provisioning service and Bluetooth Low Energy functionality.
#### Bluetooth Low Energy APIs
To use the FreeRTOS Bluetooth Low Energy middleware, you must implement some APIs.
##### APIs common between GAP for Bluetooth Classic and GAP for Bluetooth Low Energy
+ `pxBtManagerInit`
+ `pxEnable`
+ `pxDisable`
+ `pxGetDeviceProperty`
+ `pxSetDeviceProperty` (All options are mandatory expect `eBTpropertyRemoteRssi` and `eBTpropertyRemoteVersionInfo`)
+ `pxPair`
+ `pxRemoveBond`
+ `pxGetConnectionState`
+ `pxPinReply`
+ `pxSspReply`
+ `pxGetTxpower`
+ `pxGetLeAdapter`
+ `pxDeviceStateChangedCb`
+ `pxAdapterPropertiesCb`
+ `pxSspRequestCb`
+ `pxPairingStateChangedCb`
+ `pxTxPowerCb`
##### APIs specific to GAP for Bluetooth Low Energy
+ `pxRegisterBleApp`
+ `pxUnregisterBleApp`
+ `pxBleAdapterInit`
+ `pxStartAdv`
+ `pxStopAdv`
+ `pxSetAdvData`
+ `pxConnParameterUpdateRequest`
+ `pxRegisterBleAdapterCb`
+ `pxAdvStartCb`
+ `pxSetAdvDataCb`
+ `pxConnParameterUpdateRequestCb`
+ `pxCongestionCb`
##### GATT server
+ `pxRegisterServer`
+ `pxUnregisterServer`
+ `pxGattServerInit`
+ `pxAddService`
+ `pxAddIncludedService`
+ `pxAddCharacteristic`
+ `pxSetVal`
+ `pxAddDescriptor`
+ `pxStartService`
+ `pxStopService`
+ `pxDeleteService`
+ `pxSendIndication`
+ `pxSendResponse`
+ `pxMtuChangedCb`
+ `pxCongestionCb`
+ `pxIndicationSentCb`
+ `pxRequestExecWriteCb`
+ `pxRequestWriteCb`
+ `pxRequestReadCb`
+ `pxServiceDeletedCb`
+ `pxServiceStoppedCb`
+ `pxServiceStartedCb`
+ `pxDescriptorAddedCb`
+ `pxSetValCallbackCb`
+ `pxCharacteristicAddedCb`
+ `pxIncludedServiceAddedCb`
+ `pxServiceAddedCb`
+ `pxConnectionCb`
+ `pxUnregisterServerCb`
+ `pxRegisterServerCb`
For more information about porting the FreeRTOS Bluetooth Low Energy library to your platform, see [Porting the Bluetooth Low Energy Library](https://docs.aws.amazon.com/freertos/latest/portingguide/afr-porting-ble.html) in the FreeRTOS Porting Guide.
## Appendix A: MQTT over BLE GATT profile
### GATT Service Details
MQTT over BLE uses an instance of the data transfer GATT service to send MQTT Concise Binary Object Representation (CBOR) messages between the FreeRTOS device and the proxy device. The data transfer service exposes certain characteristics that help send and receive raw data over the BLE GATT protocol. It also handles the fragmentation and assembly of payloads greater than the BLE maximum transfer unit (MTU) size.
**Service UUID**
`A9D7-166A-D72E-40A9-A002-4804-4CC3-FF00`
**Service Instances**
One instance of the GATT service is created for each MQTT session with the broker. Each service has a unique UUID (two bytes) that identifies its type. Each individual instance is differentiated by the instance ID.
Each service is instantiated as a primary service on each BLE server device. You can create multiple instances of the service on a given device. The MQTT proxy service type has a unique UUID.
**Characteristics**
Characteristic content format: **CBOR**
Max characteristic value size : 512 bytes
****
[\[See the AWS documentation website for more details\]](http://docs.aws.amazon.com/freertos/latest/userguide/freertos-ble-library.html)
**GATT Procedure Requirements **
****
[\[See the AWS documentation website for more details\]](http://docs.aws.amazon.com/freertos/latest/userguide/freertos-ble-library.html)
**Message Types **
The following message types are exchanged.
****
[\[See the AWS documentation website for more details\]](http://docs.aws.amazon.com/freertos/latest/userguide/freertos-ble-library.html)
**Large Payload Transfer Characteristics **
**TXLargeMessage **
TXLargeMessage is used by the device to send a large payload that is greater than the MTU size negotiated for the BLE connection.
+ The device sends the first MTU bytes of the payload as a notification through the characteristic.
+ The proxy sends a read request on this characteristic for the remaining bytes.
+ The device sends up to the MTU size or the remaining bytes of the payload, whichever is less. Each time, it increases the offset read by the size of the payload sent.
+ The proxy will continue to read the characteristic until it gets a zero length payload or a payload less than the MTU size.
+ If the device doesn't get a read request within a specified timeout, the transfer fails and the proxy and gateway release the buffer.
+ If the proxy doesn't get a read response within a specified timeout, the transfer fails and the proxy releases the buffer.
**RXLargeMessage **
RXLargeMessage is used by the device to receive a large payload that is greater than the MTU size negotiated for the BLE connection.
+ The proxy writes messages, up to the MTU size, one by one, using write with response on this characteristic.
+ The device buffers the message until it receives a write request with zero length or a length less than the MTU size.
+ If the device doesn't get a write request within a specified timeout, the transfer fails and the device releases the buffer.
+ If the proxy doesn't get a write response within a specified timeout, the transfer fails and the proxy releases the buffer.