Generic Attribute Profile (GATT)

GATT layer manages the service database providing APIs for service registration and attribute declaration.

Services can be registered using bt_gatt_service_register() API which takes the bt_gatt_service struct that provides the list of attributes the service contains. The helper macro BT_GATT_SERVICE() can be used to declare a service.

Attributes can be declared using the bt_gatt_attr struct or using one of the helper macros:

BT_GATT_PRIMARY_SERVICE

Declares a Primary Service.

BT_GATT_SECONDARY_SERVICE

Declares a Secondary Service.

BT_GATT_INCLUDE_SERVICE

Declares a Include Service.

BT_GATT_CHARACTERISTIC

Declares a Characteristic.

BT_GATT_DESCRIPTOR

Declares a Descriptor.

BT_GATT_ATTRIBUTE

Declares an Attribute.

BT_GATT_CCC

Declares a Client Characteristic Configuration.

BT_GATT_CEP

Declares a Characteristic Extended Properties.

BT_GATT_CUD

Declares a Characteristic User Format.

Each attribute contain a uuid, which describes their type, a read callback, a write callback and a set of permission. Both read and write callbacks can be set to NULL if the attribute permission don’t allow their respective operations.

Note

Attribute read and write callbacks are called directly from RX Thread thus it is not recommended to block for long periods of time in them.

Attribute value changes can be notified using bt_gatt_notify() API, alternatively there is bt_gatt_notify_cb() where is is possible to pass a callback to be called when it is necessary to know the exact instant when the data has been transmitted over the air. Indications are supported by bt_gatt_indicate() API.

Client procedures can be enabled with the configuration option: CONFIG_BT_GATT_CLIENT

Discover procedures can be initiated with the use of bt_gatt_discover() API which takes the bt_gatt_discover_params struct which describes the type of discovery. The parameters also serves as a filter when setting the uuid field only attributes which matches will be discovered, in contrast setting it to NULL allows all attributes to be discovered.

Note

Caching discovered attributes is not supported.

Read procedures are supported by bt_gatt_read() API which takes the bt_gatt_read_params struct as parameters. In the parameters one or more attributes can be set, though setting multiple handles requires the option: CONFIG_BT_GATT_READ_MULTIPLE

Write procedures are supported by bt_gatt_write() API and takes bt_gatt_write_params struct as parameters. In case the write operation don’t require a response bt_gatt_write_without_response() or bt_gatt_write_without_response_cb() APIs can be used, with the later working similarly to bt_gatt_notify_cb().

Subscriptions to notification and indication can be initiated with use of bt_gatt_subscribe() API which takes bt_gatt_subscribe_params as parameters. Multiple subscriptions to the same attribute are supported so there could be multiple notify callback being triggered for the same attribute. Subscriptions can be removed with use of bt_gatt_unsubscribe() API.

Note

When subscriptions are removed notify callback is called with the data set to NULL.

API Reference

group bt_gatt

Generic Attribute Profile (GATT)

Defines

BT_GATT_ERR(_att_err)

Construct error return value for attribute read and write callbacks.

Return

Appropriate error code for the attribute callbacks.

Parameters

  • _att_err: ATT error code

BT_GATT_CHRC_BROADCAST

Characteristic broadcast property.

Characteristic Properties Bit field values

If set, permits broadcasts of the Characteristic Value using Server Characteristic Configuration Descriptor.

BT_GATT_CHRC_READ

Characteristic read property.

If set, permits reads of the Characteristic Value.

BT_GATT_CHRC_WRITE_WITHOUT_RESP

Characteristic write without response property.

If set, permits write of the Characteristic Value without response.

BT_GATT_CHRC_WRITE

Characteristic write with response property.

If set, permits write of the Characteristic Value with response.

BT_GATT_CHRC_NOTIFY

Characteristic notify property.

If set, permits notifications of a Characteristic Value without acknowledgment.

BT_GATT_CHRC_INDICATE

Characteristic indicate property.

If set, permits indications of a Characteristic Value with acknowledgment.

BT_GATT_CHRC_AUTH

Characteristic Authenticated Signed Writes property.

If set, permits signed writes to the Characteristic Value.

BT_GATT_CHRC_EXT_PROP

Characteristic Extended Properties property.

If set, additional characteristic properties are defined in the Characteristic Extended Properties Descriptor.

BT_GATT_CEP_RELIABLE_WRITE

Characteristic Extended Properties Bit field values

BT_GATT_CEP_WRITABLE_AUX
BT_GATT_CCC_NOTIFY

Client Characteristic Configuration Notification.

Client Characteristic Configuration Values

If set, changes to Characteristic Value shall be notified.

BT_GATT_CCC_INDICATE

Client Characteristic Configuration Indication.

If set, changes to Characteristic Value shall be indicated.

Enums

enum [anonymous]

GATT attribute permission bit field values

Values:

enumerator BT_GATT_PERM_NONE

No operations supported, e.g. for notify-only

enumerator BT_GATT_PERM_READ

Attribute read permission.

enumerator BT_GATT_PERM_WRITE

Attribute write permission.

enumerator BT_GATT_PERM_READ_ENCRYPT

Attribute read permission with encryption. 

    If set, requires encryption for read access.

enumerator BT_GATT_PERM_WRITE_ENCRYPT

Attribute write permission with encryption. 

    If set, requires encryption for write access.

enumerator BT_GATT_PERM_READ_AUTHEN

Attribute read permission with authentication. 

    If set, requires encryption using authenticated link-key for read
    access.

enumerator BT_GATT_PERM_WRITE_AUTHEN

Attribute write permission with authentication. 

    If set, requires encryption using authenticated link-key for write
    access.

enumerator BT_GATT_PERM_PREPARE_WRITE

Attribute prepare write permission. 

    If set, allows prepare writes with use of BT_GATT_WRITE_FLAG_PREPARE
    passed to write callback.

enum [anonymous]

GATT attribute write flags

Values:

enumerator BT_GATT_WRITE_FLAG_PREPARE

Attribute prepare write flag. 

   If set, write callback should only check if the device is
   authorized but no data shall be written.

enumerator BT_GATT_WRITE_FLAG_CMD

Attribute write command flag. 

   If set, indicates that write operation is a command (Write without
   response) which doesn't generate any response.

struct bt_gatt_attr
#include <gatt.h>

GATT Attribute structure.

Public Members

const struct bt_uuid *uuid

Attribute UUID

ssize_t (*read)(struct bt_conn *conn, const struct bt_gatt_attr *attr, void *buf, uint16_t len, uint16_t offset)

Attribute read callback.

The callback can also be used locally to read the contents of the attribute in which case no connection will be set.

Return

Number fo bytes read, or in case of an error BT_GATT_ERR() with a specific ATT error code.

Parameters

  • conn: The connection that is requesting to read

  • attr: The attribute that’s being read

  • buf: Buffer to place the read result in

  • len: Length of data to read

  • offset: Offset to start reading from

ssize_t (*write)(struct bt_conn *conn, const struct bt_gatt_attr *attr, const void *buf, uint16_t len, uint16_t offset, uint8_t flags)

Attribute write callback.

Return

Number of bytes written, or in case of an error BT_GATT_ERR() with a specific ATT error code.

Parameters

  • conn: The connection that is requesting to write

  • attr: The attribute that’s being written

  • buf: Buffer with the data to write

  • len: Number of bytes in the buffer

  • offset: Offset to start writing from

  • flags: Flags (BT_GATT_WRITE_*)

void *user_data

Attribute user data

uint16_t handle

Attribute handle

uint8_t perm

Attribute permissions

struct bt_gatt_service_static
#include <gatt.h>

GATT Service structure.

Public Members

const struct bt_gatt_attr *attrs

Service Attributes

size_t attr_count

Service Attribute count

struct bt_gatt_service
#include <gatt.h>

GATT Service structure.

Public Members

struct bt_gatt_attr *attrs

Service Attributes

size_t attr_count

Service Attribute count

struct bt_gatt_service_val
#include <gatt.h>

Service Attribute Value.

Public Members

const struct bt_uuid *uuid

Service UUID.

uint16_t end_handle

Service end handle.

struct bt_gatt_include
#include <gatt.h>

Include Attribute Value.

Public Members

const struct bt_uuid *uuid

Service UUID.

uint16_t start_handle

Service start handle.

uint16_t end_handle

Service end handle.

struct bt_gatt_chrc
#include <gatt.h>

Characteristic Attribute Value.

Public Members

const struct bt_uuid *uuid

Characteristic UUID.

uint16_t value_handle

Characteristic Value handle.

uint8_t properties

Characteristic properties.

struct bt_gatt_cep
#include <gatt.h>

Characteristic Extended Properties Attribute Value.

Public Members

uint16_t properties

Characteristic Extended properties

struct bt_gatt_ccc
#include <gatt.h>

Client Characteristic Configuration Attribute Value

Public Members

uint16_t flags

Client Characteristic Configuration flags

struct bt_gatt_cpf
#include <gatt.h>

GATT Characteristic Presentation Format Attribute Value.

Public Members

uint8_t format

Format of the value of the characteristic

int8_t exponent

Exponent field to determine how the value of this characteristic is further formatted

uint16_t unit

Unit of the characteristic

uint8_t name_space

Name space of the description

uint16_t description

Description of the characteristic as defined in a higher layer profile

GATT Server

group bt_gatt_server

Defines

BT_GATT_SERVICE_DEFINE(_name, ...)

Statically define and register a service.

Helper macro to statically define and register a service.

Parameters

  • _name: Service name.

BT_GATT_SERVICE_INSTANCE_DEFINE(_name, _instances, _instance_num, _attrs_def)

Statically define service structure array.

Helper macro to statically define service structure array. Each element of the array is linked to the service attribute array which is also defined in this scope using _attrs_def macro.

Parameters

  • _name: Name of service structure array.

  • _instances: Array of instances to pass as user context to the attribute callbacks.

  • _instance_num: Number of elements in instance array.

  • _attrs_def: Macro provided by the user that defines attribute array for the serivce. This macro should accept single parameter which is the instance context.

BT_GATT_SERVICE(_attrs)

Service Structure Declaration Macro.

Helper macro to declare a service structure.

Parameters

  • _attrs: Service attributes.

BT_GATT_PRIMARY_SERVICE(_service)

Primary Service Declaration Macro.

Helper macro to declare a primary service attribute.

Parameters

  • _service: Service attribute value.

BT_GATT_SECONDARY_SERVICE(_service)

Secondary Service Declaration Macro.

Helper macro to declare a secondary service attribute.

Parameters

  • _service: Service attribute value.

BT_GATT_INCLUDE_SERVICE(_service_incl)

Include Service Declaration Macro.

Helper macro to declare database internal include service attribute.

Parameters

  • _service_incl: the first service attribute of service to include

BT_GATT_CHRC_INIT(_uuid, _handle, _props)
BT_GATT_CHARACTERISTIC(_uuid, _props, _perm, _read, _write, _value)

Characteristic and Value Declaration Macro.

Helper macro to declare a characteristic attribute along with its attribute value.

Parameters

  • _uuid: Characteristic attribute uuid.

  • _props: Characteristic attribute properties.

  • _perm: Characteristic Attribute access permissions.

  • _read: Characteristic Attribute read callback.

  • _write: Characteristic Attribute write callback.

  • _value: Characteristic Attribute value.

BT_GATT_CCC_MAX
BT_GATT_CCC_INITIALIZER(_changed, _write, _match)

Initialize Client Characteristic Configuration Declaration Macro.

Helper macro to initialize a Managed CCC attribute value.

Parameters

  • _changed: Configuration changed callback.

  • _write: Configuration write callback.

  • _match: Configuration match callback.

BT_GATT_CCC_MANAGED(_ccc, _perm)

Managed Client Characteristic Configuration Declaration Macro.

Helper macro to declare a Managed CCC attribute.

Parameters

  • _ccc: CCC attribute user data, shall point to a _bt_gatt_ccc.

  • _perm: CCC access permissions.

BT_GATT_CCC(_changed, _perm)

Client Characteristic Configuration Declaration Macro.

Helper macro to declare a CCC attribute.

Parameters

  • _changed: Configuration changed callback.

  • _perm: CCC access permissions.

BT_GATT_CEP(_value)

Characteristic Extended Properties Declaration Macro.

Helper macro to declare a CEP attribute.

Parameters

  • _value: Descriptor attribute value.

BT_GATT_CUD(_value, _perm)

Characteristic User Format Descriptor Declaration Macro.

Helper macro to declare a CUD attribute.

Parameters

  • _value: User description NULL-terminated C string.

  • _perm: Descriptor attribute access permissions.

BT_GATT_CPF(_value)

Characteristic Presentation Format Descriptor Declaration Macro.

Helper macro to declare a CPF attribute.

Parameters

  • _value: Descriptor attribute value.

BT_GATT_DESCRIPTOR(_uuid, _perm, _read, _write, _value)

Descriptor Declaration Macro.

Helper macro to declare a descriptor attribute.

Parameters

  • _uuid: Descriptor attribute uuid.

  • _perm: Descriptor attribute access permissions.

  • _read: Descriptor attribute read callback.

  • _write: Descriptor attribute write callback.

  • _value: Descriptor attribute value.

BT_GATT_ATTRIBUTE(_uuid, _perm, _read, _write, _value)

Attribute Declaration Macro.

Helper macro to declare an attribute.

Parameters

  • _uuid: Attribute uuid.

  • _perm: Attribute access permissions.

  • _read: Attribute read callback.

  • _write: Attribute write callback.

  • _value: Attribute value.

Typedefs

typedef uint8_t (*bt_gatt_attr_func_t)(const struct bt_gatt_attr *attr, uint16_t handle, void *user_data)

Attribute iterator callback.

Return

BT_GATT_ITER_CONTINUE if should continue to the next attribute.

Return

BT_GATT_ITER_STOP to stop.

Parameters

  • attr: Attribute found.

  • handle: Attribute handle found.

  • user_data: Data given.

typedef void (*bt_gatt_complete_func_t)(struct bt_conn *conn, void *user_data)

Notification complete result callback.

Parameters

  • conn: Connection object.

  • user_data: Data passed in by the user.

typedef void (*bt_gatt_indicate_func_t)(struct bt_conn *conn, struct bt_gatt_indicate_params *params, uint8_t err)

Indication complete result callback.

Parameters

  • conn: Connection object.

  • params: Indication params object.

  • err: ATT error code

typedef void (*bt_gatt_indicate_params_destroy_t)(struct bt_gatt_indicate_params *params)

Enums

enum [anonymous]

Values:

enumerator BT_GATT_ITER_STOP
enumerator BT_GATT_ITER_CONTINUE

Functions

int bt_gatt_service_register(struct bt_gatt_service *svc)

Register GATT service.

Register GATT service. Applications can make use of macros such as BT_GATT_PRIMARY_SERVICE, BT_GATT_CHARACTERISTIC, BT_GATT_DESCRIPTOR, etc.

When using CONFIG_BT_SETTINGS then all services that should have bond configuration loaded, i.e. CCC values, must be registered before calling settings_load.

When using CONFIG_BT_GATT_CACHING and CONFIG_BT_SETTINGS then all services that should be included in the GATT Database Hash calculation should be added before calling settings_load. All services registered after settings_load will trigger a new database hash calculation and a new hash stored.

Return

0 in case of success or negative value in case of error.

Parameters

  • svc: Service containing the available attributes

int bt_gatt_service_unregister(struct bt_gatt_service *svc)

Unregister GATT service. *.

Return

0 in case of success or negative value in case of error.

Parameters

  • svc: Service to be unregistered.

void bt_gatt_foreach_attr_type(uint16_t start_handle, uint16_t end_handle, const struct bt_uuid *uuid, const void *attr_data, uint16_t num_matches, bt_gatt_attr_func_t func, void *user_data)

Attribute iterator by type.

Iterate attributes in the given range matching given UUID and/or data.

Parameters

  • start_handle: Start handle.

  • end_handle: End handle.

  • uuid: UUID to match, passing NULL skips UUID matching.

  • attr_data: Attribute data to match, passing NULL skips data matching.

  • num_matches: Number matches, passing 0 makes it unlimited.

  • func: Callback function.

  • user_data: Data to pass to the callback.

static inline void bt_gatt_foreach_attr(uint16_t start_handle, uint16_t end_handle, bt_gatt_attr_func_t func, void *user_data)

Attribute iterator.

Iterate attributes in the given range.

Parameters

  • start_handle: Start handle.

  • end_handle: End handle.

  • func: Callback function.

  • user_data: Data to pass to the callback.

struct bt_gatt_attr *bt_gatt_attr_next(const struct bt_gatt_attr *attr)

Iterate to the next attribute.

Iterate to the next attribute following a given attribute.

Return

The next attribute or NULL if it cannot be found.

Parameters

  • attr: Current Attribute.

uint16_t bt_gatt_attr_get_handle(const struct bt_gatt_attr *attr)

Get Attribute handle.

Return

Handle of the corresponding attribute or zero if the attribute could not be found.

Parameters

  • attr: Attribute object.

uint16_t bt_gatt_attr_value_handle(const struct bt_gatt_attr *attr)

Get the handle of the characteristic value descriptor.

Note

The user_data of the attribute must of type bt_gatt_chrc.

Return

the handle of the corresponding Characteristic Value. The value will be zero (the invalid handle) if attr was not a characteristic attribute.

Parameters

  • attr: A Characteristic Attribute.

ssize_t bt_gatt_attr_read(struct bt_conn *conn, const struct bt_gatt_attr *attr, void *buf, uint16_t buf_len, uint16_t offset, const void *value, uint16_t value_len)

Generic Read Attribute value helper.

Read attribute value from local database storing the result into buffer.

Return

number of bytes read in case of success or negative values in case of error.

Parameters

  • conn: Connection object.

  • attr: Attribute to read.

  • buf: Buffer to store the value.

  • buf_len: Buffer length.

  • offset: Start offset.

  • value: Attribute value.

  • value_len: Length of the attribute value.

ssize_t bt_gatt_attr_read_service(struct bt_conn *conn, const struct bt_gatt_attr *attr, void *buf, uint16_t len, uint16_t offset)

Read Service Attribute helper.

Read service attribute value from local database storing the result into buffer after encoding it.

Note

Only use this with attributes which user_data is a bt_uuid.

Return

number of bytes read in case of success or negative values in case of error.

Parameters

  • conn: Connection object.

  • attr: Attribute to read.

  • buf: Buffer to store the value read.

  • len: Buffer length.

  • offset: Start offset.

ssize_t bt_gatt_attr_read_included(struct bt_conn *conn, const struct bt_gatt_attr *attr, void *buf, uint16_t len, uint16_t offset)

Read Include Attribute helper.

Read include service attribute value from local database storing the result into buffer after encoding it.

Note

Only use this with attributes which user_data is a bt_gatt_include.

Return

number of bytes read in case of success or negative values in case of error.

Parameters

  • conn: Connection object.

  • attr: Attribute to read.

  • buf: Buffer to store the value read.

  • len: Buffer length.

  • offset: Start offset.

ssize_t bt_gatt_attr_read_chrc(struct bt_conn *conn, const struct bt_gatt_attr *attr, void *buf, uint16_t len, uint16_t offset)

Read Characteristic Attribute helper.

Read characteristic attribute value from local database storing the result into buffer after encoding it.

Note

Only use this with attributes which user_data is a bt_gatt_chrc.

Return

number of bytes read in case of success or negative values in case of error.

Parameters

  • conn: Connection object.

  • attr: Attribute to read.

  • buf: Buffer to store the value read.

  • len: Buffer length.

  • offset: Start offset.

ssize_t bt_gatt_attr_read_ccc(struct bt_conn *conn, const struct bt_gatt_attr *attr, void *buf, uint16_t len, uint16_t offset)

Read Client Characteristic Configuration Attribute helper.

Read CCC attribute value from local database storing the result into buffer after encoding it.

Note

Only use this with attributes which user_data is a _bt_gatt_ccc.

Return

number of bytes read in case of success or negative values in case of error.

Parameters

  • conn: Connection object.

  • attr: Attribute to read.

  • buf: Buffer to store the value read.

  • len: Buffer length.

  • offset: Start offset.

ssize_t bt_gatt_attr_write_ccc(struct bt_conn *conn, const struct bt_gatt_attr *attr, const void *buf, uint16_t len, uint16_t offset, uint8_t flags)

Write Client Characteristic Configuration Attribute helper.

Write value in the buffer into CCC attribute.

Note

Only use this with attributes which user_data is a _bt_gatt_ccc.

Return

number of bytes written in case of success or negative values in case of error.

Parameters

  • conn: Connection object.

  • attr: Attribute to read.

  • buf: Buffer to store the value read.

  • len: Buffer length.

  • offset: Start offset.

  • flags: Write flags.

ssize_t bt_gatt_attr_read_cep(struct bt_conn *conn, const struct bt_gatt_attr *attr, void *buf, uint16_t len, uint16_t offset)

Read Characteristic Extended Properties Attribute helper.

Read CEP attribute value from local database storing the result into buffer after encoding it.

Note

Only use this with attributes which user_data is a bt_gatt_cep.

Return

number of bytes read in case of success or negative values in case of error.

Parameters

  • conn: Connection object

  • attr: Attribute to read

  • buf: Buffer to store the value read

  • len: Buffer length

  • offset: Start offset

ssize_t bt_gatt_attr_read_cud(struct bt_conn *conn, const struct bt_gatt_attr *attr, void *buf, uint16_t len, uint16_t offset)

Read Characteristic User Description Descriptor Attribute helper.

Read CUD attribute value from local database storing the result into buffer after encoding it.

Note

Only use this with attributes which user_data is a NULL-terminated C string.

Return

number of bytes read in case of success or negative values in case of error.

Parameters

  • conn: Connection object

  • attr: Attribute to read

  • buf: Buffer to store the value read

  • len: Buffer length

  • offset: Start offset

ssize_t bt_gatt_attr_read_cpf(struct bt_conn *conn, const struct bt_gatt_attr *attr, void *buf, uint16_t len, uint16_t offset)

Read Characteristic Presentation format Descriptor Attribute helper.

Read CPF attribute value from local database storing the result into buffer after encoding it.

Note

Only use this with attributes which user_data is a bt_gatt_pf.

Return

number of bytes read in case of success or negative values in case of error.

Parameters

  • conn: Connection object

  • attr: Attribute to read

  • buf: Buffer to store the value read

  • len: Buffer length

  • offset: Start offset

int bt_gatt_notify_cb(struct bt_conn *conn, struct bt_gatt_notify_params *params)

Notify attribute value change.

This function works in the same way as bt_gatt_notify. With the addition that after sending the notification the callback function will be called.

The callback is run from System Workqueue context.

Alternatively it is possible to notify by UUID by setting it on the parameters, when using this method the attribute given is used as the start range when looking up for possible matches.

Return

0 in case of success or negative value in case of error.

Parameters

  • conn: Connection object.

  • params: Notification parameters.

int bt_gatt_notify_multiple(struct bt_conn *conn, uint16_t num_params, struct bt_gatt_notify_params *params)

Notify multiple attribute value change.

Return

0 in case of success or negative value in case of error.

Parameters

  • conn: Connection object.

  • num_params: Number of notification parameters.

  • params: Array of notification parameters.

static inline int bt_gatt_notify(struct bt_conn *conn, const struct bt_gatt_attr *attr, const void *data, uint16_t len)

Notify attribute value change.

Send notification of attribute value change, if connection is NULL notify all peer that have notification enabled via CCC otherwise do a direct notification only the given connection.

The attribute object on the parameters can be the so called Characteristic Declaration, which is usually declared with BT_GATT_CHARACTERISTIC followed by BT_GATT_CCC, or the Characteristic Value Declaration which is automatically created after the Characteristic Declaration when using BT_GATT_CHARACTERISTIC.

Return

0 in case of success or negative value in case of error.

Parameters

  • conn: Connection object.

  • attr: Characteristic or Characteristic Value attribute.

  • data: Pointer to Attribute data.

  • len: Attribute value length.

static inline int bt_gatt_notify_uuid(struct bt_conn *conn, const struct bt_uuid *uuid, const struct bt_gatt_attr *attr, const void *data, uint16_t len)

Notify attribute value change by UUID.

Send notification of attribute value change, if connection is NULL notify all peer that have notification enabled via CCC otherwise do a direct notification only on the given connection.

The attribute object is the starting point for the search of the UUID.

Return

0 in case of success or negative value in case of error.

Parameters

  • conn: Connection object.

  • uuid: The UUID. If the server contains multiple services with the same UUID, then the first occurrence, starting from the attr given, is used.

  • attr: Pointer to an attribute that serves as the starting point for the search of a match for the UUID.

  • data: Pointer to Attribute data.

  • len: Attribute value length.

int bt_gatt_indicate(struct bt_conn *conn, struct bt_gatt_indicate_params *params)

Indicate attribute value change.

Send an indication of attribute value change. if connection is NULL indicate all peer that have notification enabled via CCC otherwise do a direct indication only the given connection.

The attribute object on the parameters can be the so called Characteristic Declaration, which is usually declared with BT_GATT_CHARACTERISTIC followed by BT_GATT_CCC, or the Characteristic Value Declaration which is automatically created after the Characteristic Declaration when using BT_GATT_CHARACTERISTIC.

The callback is run from System Workqueue context.

Alternatively it is possible to indicate by UUID by setting it on the parameters, when using this method the attribute given is used as the start range when looking up for possible matches.

Note

This procedure is asynchronous therefore the parameters need to remains valid while it is active. The procedure is active until the destroy callback is run.

Return

0 in case of success or negative value in case of error.

Parameters

  • conn: Connection object.

  • params: Indicate parameters.

bool bt_gatt_is_subscribed(struct bt_conn *conn, const struct bt_gatt_attr *attr, uint16_t ccc_value)

Check if connection have subscribed to attribute.

Check if connection has subscribed to attribute value change.

The attribute object can be the so called Characteristic Declaration, which is usually declared with BT_GATT_CHARACTERISTIC followed by BT_GATT_CCC, or the Characteristic Value Declaration which is automatically created after the Characteristic Declaration when using BT_GATT_CHARACTERISTIC, or the Client Characteristic Configuration Descriptor (CCCD) which is created by BT_GATT_CCC.

Return

true if the attribute object has been subscribed.

Parameters

  • conn: Connection object.

  • attr: Attribute object.

  • ccc_value: The subscription type, either notifications or indications.

uint16_t bt_gatt_get_mtu(struct bt_conn *conn)

Get ATT MTU for a connection.

Get negotiated ATT connection MTU, note that this does not equal the largest amount of attribute data that can be transferred within a single packet.

Return

MTU in bytes

Parameters

  • conn: Connection object.

struct bt_gatt_ccc_cfg
#include <gatt.h>

GATT CCC configuration entry.

Public Members

uint8_t id

Local identity, BT_ID_DEFAULT in most cases.

bt_addr_le_t peer

Remote peer address.

uint16_t value

Configuration value.

struct bt_gatt_notify_params
#include <gatt.h>

Public Members

const struct bt_uuid *uuid

Notification Attribute UUID type

const struct bt_gatt_attr *attr

Notification Attribute object

const void *data

Notification Value data

uint16_t len

Notification Value length

bt_gatt_complete_func_t func

Notification Value callback

void *user_data

Notification Value callback user data

struct bt_gatt_indicate_params
#include <gatt.h>

GATT Indicate Value parameters.

Public Members

const struct bt_uuid *uuid

Notification Attribute UUID type

const struct bt_gatt_attr *attr

Indicate Attribute object

bt_gatt_indicate_func_t func

Indicate Value callback

bt_gatt_indicate_params_destroy_t destroy

Indicate operation complete callback

const void *data

Indicate Value data

uint16_t len

Indicate Value length

GATT Client

group bt_gatt_client

Typedefs

typedef uint8_t (*bt_gatt_discover_func_t)(struct bt_conn *conn, const struct bt_gatt_attr *attr, struct bt_gatt_discover_params *params)

Discover attribute callback function.

If discovery procedure has completed this callback will be called with attr set to NULL. This will not happen if procedure was stopped by returning BT_GATT_ITER_STOP.

Parameters

  • conn: Connection object.

  • attr: Attribute found, or NULL if not found.

  • params: Discovery parameters given.

The attribute object as well as its UUID and value objects are temporary and must be copied to in order to cache its information. Only the following fields of the attribute contains valid information:

  • uuid UUID representing the type of attribute.

  • handle Handle in the remote database.

  • user_data The value of the attribute. Will be NULL when discovering descriptors

To be able to read the value of the discovered attribute the user_data must be cast to an appropriate type.

Return

BT_GATT_ITER_CONTINUE to continue discovery procedure.

Return

BT_GATT_ITER_STOP to stop discovery procedure.

typedef uint8_t (*bt_gatt_read_func_t)(struct bt_conn *conn, uint8_t err, struct bt_gatt_read_params *params, const void *data, uint16_t length)

Read callback function.

Return

BT_GATT_ITER_CONTINUE if should continue to the next attribute.

Return

BT_GATT_ITER_STOP to stop.

Parameters

  • conn: Connection object.

  • err: ATT error code.

  • params: Read parameters used.

  • data: Attribute value data. NULL means read has completed.

  • length: Attribute value length.

typedef void (*bt_gatt_write_func_t)(struct bt_conn *conn, uint8_t err, struct bt_gatt_write_params *params)

Write callback function.

Parameters

  • conn: Connection object.

  • err: ATT error code.

  • params: Write parameters used.

typedef uint8_t (*bt_gatt_notify_func_t)(struct bt_conn *conn, struct bt_gatt_subscribe_params *params, const void *data, uint16_t length)

Notification callback function.

Return

BT_GATT_ITER_CONTINUE to continue receiving value notifications. BT_GATT_ITER_STOP to unsubscribe from value notifications.

Parameters

  • conn: Connection object. May be NULL, indicating that the peer is being unpaired

  • params: Subscription parameters.

  • data: Attribute value data. If NULL then subscription was removed.

  • length: Attribute value length.

Enums

enum [anonymous]

GATT Discover types

Values:

enumerator BT_GATT_DISCOVER_PRIMARY

Discover Primary Services.

enumerator BT_GATT_DISCOVER_SECONDARY

Discover Secondary Services.

enumerator BT_GATT_DISCOVER_INCLUDE

Discover Included Services.

enumerator BT_GATT_DISCOVER_CHARACTERISTIC

Discover Characteristic Values. 

    Discover Characteristic Value and its properties.

enumerator BT_GATT_DISCOVER_DESCRIPTOR

Discover Descriptors. 

    Discover Attributes which are not services or characteristics.

    @note The use of this type of discover is not recommended for
          discovering in ranges across multiple services/characteristics
          as it may incur in extra round trips.

enumerator BT_GATT_DISCOVER_ATTRIBUTE

Discover Attributes. 

    Discover Attributes of any type.

    @note The use of this type of discover is not recommended for
          discovering in ranges across multiple services/characteristics
          as it may incur in more round trips.

enum [anonymous]

Subscription flags

Values:

enumerator BT_GATT_SUBSCRIBE_FLAG_VOLATILE

Persistence flag. 

    If set, indicates that the subscription is not saved
    on the GATT server side. Therefore, upon disconnection,
    the subscription will be automatically removed
    from the client's subscriptions list and
    when the client reconnects, it will have to
    issue a new subscription.

enumerator BT_GATT_SUBSCRIBE_FLAG_NO_RESUB

No resubscribe flag. 

    By default when BT_GATT_SUBSCRIBE_FLAG_VOLATILE is unset, the
    subscription will be automatically renewed when the client
    reconnects, as a workaround for GATT servers that do not persist
    subscriptions.

    This flag will disable the automatic resubscription. It is useful
    if the application layer knows that the GATT server remembers
    subscriptions from previous connections and wants to avoid renewing
    the subscriptions.

enumerator BT_GATT_SUBSCRIBE_FLAG_WRITE_PENDING

Write pending flag. 

    If set, indicates write operation is pending waiting remote end to
    respond.

enumerator BT_GATT_SUBSCRIBE_NUM_FLAGS

Functions

int bt_gatt_exchange_mtu(struct bt_conn *conn, struct bt_gatt_exchange_params *params)

Exchange MTU.

This client procedure can be used to set the MTU to the maximum possible size the buffers can hold.

Note

Shall only be used once per connection.

Return

0 in case of success or negative value in case of error.

Parameters

  • conn: Connection object.

  • params: Exchange MTU parameters.

int bt_gatt_discover(struct bt_conn *conn, struct bt_gatt_discover_params *params)

GATT Discover function.

This procedure is used by a client to discover attributes on a server.

Primary Service Discovery: Procedure allows to discover specific Primary Service based on UUID. Include Service Discovery: Procedure allows to discover all Include Services within specified range. Characteristic Discovery: Procedure allows to discover all characteristics within specified handle range as well as discover characteristics with specified UUID. Descriptors Discovery: Procedure allows to discover all characteristic descriptors within specified range.

For each attribute found the callback is called which can then decide whether to continue discovering or stop.

Note

This procedure is asynchronous therefore the parameters need to remains valid while it is active.

Return

0 in case of success or negative value in case of error.

Parameters

  • conn: Connection object.

  • params: Discover parameters.

int bt_gatt_read(struct bt_conn *conn, struct bt_gatt_read_params *params)

Read Attribute Value by handle.

This procedure read the attribute value and return it to the callback.

When reading attributes by UUID the callback can be called multiple times depending on how many instances of given the UUID exists with the start_handle being updated for each instance.

If an instance does contain a long value which cannot be read entirely the caller will need to read the remaining data separately using the handle and offset.

Note

This procedure is asynchronous therefore the parameters need to remains valid while it is active.

Return

0 in case of success or negative value in case of error.

Parameters

  • conn: Connection object.

  • params: Read parameters.

int bt_gatt_write(struct bt_conn *conn, struct bt_gatt_write_params *params)

Write Attribute Value by handle.

This procedure write the attribute value and return the result in the callback.

Note

This procedure is asynchronous therefore the parameters need to remains valid while it is active.

Return

0 in case of success or negative value in case of error.

Parameters

  • conn: Connection object.

  • params: Write parameters.

int bt_gatt_write_without_response_cb(struct bt_conn *conn, uint16_t handle, const void *data, uint16_t length, bool sign, bt_gatt_complete_func_t func, void *user_data)

Write Attribute Value by handle without response with callback.

This function works in the same way as bt_gatt_write_without_response. With the addition that after sending the write the callback function will be called.

The callback is run from System Workqueue context.

Note

By using a callback it also disable the internal flow control which would prevent sending multiple commands without waiting for their transmissions to complete, so if that is required the caller shall not submit more data until the callback is called.

Return

0 in case of success or negative value in case of error.

Parameters

  • conn: Connection object.

  • handle: Attribute handle.

  • data: Data to be written.

  • length: Data length.

  • sign: Whether to sign data

  • func: Transmission complete callback.

  • user_data: User data to be passed back to callback.

static inline int bt_gatt_write_without_response(struct bt_conn *conn, uint16_t handle, const void *data, uint16_t length, bool sign)

Write Attribute Value by handle without response.

This procedure write the attribute value without requiring an acknowledgment that the write was successfully performed

Return

0 in case of success or negative value in case of error.

Parameters

  • conn: Connection object.

  • handle: Attribute handle.

  • data: Data to be written.

  • length: Data length.

  • sign: Whether to sign data

int bt_gatt_subscribe(struct bt_conn *conn, struct bt_gatt_subscribe_params *params)

Subscribe Attribute Value Notification.

This procedure subscribe to value notification using the Client Characteristic Configuration handle. If notification received subscribe value callback is called to return notified value. One may then decide whether to unsubscribe directly from this callback. Notification callback with NULL data will not be called if subscription was removed by this method.

Note

Notifications are asynchronous therefore the parameters need to remain valid while subscribed.

Return

0 in case of success or negative value in case of error.

Parameters

  • conn: Connection object.

  • params: Subscribe parameters.

int bt_gatt_resubscribe(uint8_t id, const bt_addr_le_t *peer, struct bt_gatt_subscribe_params *params)

Resubscribe Attribute Value Notification subscription.

Resubscribe to Attribute Value Notification when already subscribed from a previous connection. The GATT server will remember subscription from previous connections when bonded, so resubscribing can be done without performing a new subscribe procedure after a power cycle.

Note

Notifications are asynchronous therefore the parameters need to remain valid while subscribed.

Return

0 in case of success or negative value in case of error.

Parameters

  • id: Local identity (in most cases BT_ID_DEFAULT).

  • peer: Remote address.

  • params: Subscribe parameters.

int bt_gatt_unsubscribe(struct bt_conn *conn, struct bt_gatt_subscribe_params *params)

Unsubscribe Attribute Value Notification.

This procedure unsubscribe to value notification using the Client Characteristic Configuration handle. Notification callback with NULL data will be called if subscription was removed by this call, until then the parameters cannot be reused.

Return

0 in case of success or negative value in case of error.

Parameters

  • conn: Connection object.

  • params: Subscribe parameters.

void bt_gatt_cancel(struct bt_conn *conn, void *params)

Cancel GATT pending request.

Parameters

  • conn: Connection object.

  • params: Requested params address.

struct bt_gatt_exchange_params
#include <gatt.h>

GATT Exchange MTU parameters.

Public Members

void (*func)(struct bt_conn *conn, uint8_t err, struct bt_gatt_exchange_params *params)

Response callback

struct bt_gatt_discover_params
#include <gatt.h>

GATT Discover Attributes parameters.

Public Members

const struct bt_uuid *uuid

Discover UUID type

bt_gatt_discover_func_t func

Discover attribute callback

uint16_t end_handle

Discover end handle

uint8_t type

Discover type

struct bt_gatt_read_params
#include <gatt.h>

GATT Read parameters.

Public Members

bt_gatt_read_func_t func

Read attribute callback.

size_t handle_count

If equals to 1 single.handle and single.offset are used. If >1 Read Multiple Characteristic Values is performed and handles are used. If equals to 0 by_uuid is used for Read Using Characteristic UUID.

struct bt_gatt_write_params
#include <gatt.h>

GATT Write parameters.

Public Members

bt_gatt_write_func_t func

Response callback

uint16_t handle

Attribute handle

uint16_t offset

Attribute data offset

const void *data

Data to be written

uint16_t length

Length of the data

struct bt_gatt_subscribe_params
#include <gatt.h>

GATT Subscribe parameters.

Public Functions

ATOMIC_DEFINE (flags, BT_GATT_SUBSCRIBE_NUM_FLAGS)

Subscription flags

Public Members

bt_gatt_notify_func_t notify

Notification value callback

bt_gatt_write_func_t write

Subscribe CCC write request response callback

uint16_t value_handle

Subscribe value handle

uint16_t ccc_handle

Subscribe CCC handle

uint16_t value

Subscribe value