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.

Parameters

  • _att_err – ATT error code

Returns

Appropriate error code for the attribute callbacks.

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.

BT_GATT_SCC_BROADCAST

Server Characteristic Configuration Broadcast.

Server Characteristic Configuration Values

If set, the characteristic value shall be broadcast in the advertising data when the server is advertising.

Enums

enum [anonymous]

GATT attribute permission bit field values

Values:

enumerator BT_GATT_PERM_NONE = 0

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

enumerator BT_GATT_PERM_READ = BIT(0)

Attribute read permission.

enumerator BT_GATT_PERM_WRITE = BIT(1)

Attribute write permission.

enumerator BT_GATT_PERM_READ_ENCRYPT = BIT(2)

Attribute read permission with encryption. 

    If set, requires encryption for read access.

enumerator BT_GATT_PERM_WRITE_ENCRYPT = BIT(3)

Attribute write permission with encryption. 

    If set, requires encryption for write access.

enumerator BT_GATT_PERM_READ_AUTHEN = BIT(4)

Attribute read permission with authentication. 

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

enumerator BT_GATT_PERM_WRITE_AUTHEN = BIT(5)

Attribute write permission with authentication. 

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

enumerator BT_GATT_PERM_PREPARE_WRITE = BIT(6)

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 = BIT(0)

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 = BIT(1)

Attribute write command flag. 

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

enumerator BT_GATT_WRITE_FLAG_EXECUTE = BIT(2)

Attribute write execute flag. 

   If set, indicates that write operation is a execute, which indicates
   the end of a long write, and will come after 1 or more
   @ref BT_GATT_WRITE_FLAG_PREPARE.

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.

Param conn

The connection that is requesting to read

Param attr

The attribute that’s being read

Param buf

Buffer to place the read result in

Param len

Length of data to read

Param offset

Offset to start reading from

Return

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

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.

Param conn

The connection that is requesting to write

Param attr

The attribute that’s being written

Param buf

Buffer with the data to write

Param len

Number of bytes in the buffer

Param offset

Offset to start writing from

Param flags

Flags (BT_GATT_WRITE_*)

Return

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

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_cb
#include <gatt.h>

GATT callback structure.

Public Members

void (*att_mtu_updated)(struct bt_conn *conn, uint16_t tx, uint16_t rx)

The maximum ATT MTU on a connection has changed.

This callback notifies the application that the maximum TX or RX ATT MTU has increased.

Param conn

Connection object.

Param tx

Updated TX ATT MTU.

Param rx

Updated RX ATT MTU.

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_scc
#include <gatt.h>

Server Characterestic Configuration Attribute Value

Public Members

uint16_t flags

Server 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, _user_data)

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.

  • _user_data – Characteristic Attribute user data.

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

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.

  • _user_data – Descriptor attribute user data.

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

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.

  • _user_data – Attribute user data.

Typedefs

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

Attribute iterator callback.

Param attr

Attribute found.

Param handle

Attribute handle found.

Param user_data

Data given.

Return

BT_GATT_ITER_CONTINUE if should continue to the next attribute.

Return

BT_GATT_ITER_STOP to stop.

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

Notification complete result callback.

Param conn

Connection object.

Param 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.

Param conn

Connection object.

Param params

Indication params object.

Param 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 = 0
enumerator BT_GATT_ITER_CONTINUE

Functions

void bt_gatt_cb_register(struct bt_gatt_cb *cb)

Register GATT callbacks.

Register callbacks to monitor the state of GATT.

Parameters

  • cb – Callback struct.

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.

Parameters

  • svc – Service containing the available attributes

Returns

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

int bt_gatt_service_unregister(struct bt_gatt_service *svc)

Unregister GATT service.

Parameters

  • svc – Service to be unregistered.

Returns

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

bool bt_gatt_service_is_registered(const struct bt_gatt_service *svc)

Check if GATT service is registered.

Parameters

  • svc – Service to be checked.

Returns

true if registered or false if not register.

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.

Parameters

  • attr – Current Attribute.

Returns

The next attribute or NULL if it cannot be found.

struct bt_gatt_attr *bt_gatt_find_by_uuid(const struct bt_gatt_attr *attr, uint16_t attr_count, const struct bt_uuid *uuid)

Find Attribute by UUID.

Find the attribute with the matching UUID. To limit the search to a service set the attr to the service attributes and the attr_count to the service attribute count .

Parameters

  • attr – Pointer to an attribute that serves as the starting point for the search of a match for the UUID. Passing NULL will search the entire range.

  • attr_count – The number of attributes from the starting point to search for a match for the UUID. Set to 0 to search until the end.

  • uuid – UUID to match.

uint16_t bt_gatt_attr_get_handle(const struct bt_gatt_attr *attr)

Get Attribute handle.

Parameters

  • attr – Attribute object.

Returns

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

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.

Parameters

  • attr – A Characteristic Attribute.

Returns

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

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.

Returns

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

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.

Parameters

  • conn – Connection object.

  • attr – Attribute to read.

  • buf – Buffer to store the value read.

  • len – Buffer length.

  • offset – Start offset.

Returns

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

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.

Parameters

  • conn – Connection object.

  • attr – Attribute to read.

  • buf – Buffer to store the value read.

  • len – Buffer length.

  • offset – Start offset.

Returns

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

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.

Parameters

  • conn – Connection object.

  • attr – Attribute to read.

  • buf – Buffer to store the value read.

  • len – Buffer length.

  • offset – Start offset.

Returns

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

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.

Parameters

  • conn – Connection object.

  • attr – Attribute to read.

  • buf – Buffer to store the value read.

  • len – Buffer length.

  • offset – Start offset.

Returns

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

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.

Parameters

  • conn – Connection object.

  • attr – Attribute to read.

  • buf – Buffer to store the value read.

  • len – Buffer length.

  • offset – Start offset.

  • flags – Write flags.

Returns

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

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.

Parameters

  • conn – Connection object

  • attr – Attribute to read

  • buf – Buffer to store the value read

  • len – Buffer length

  • offset – Start offset

Returns

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

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.

Parameters

  • conn – Connection object

  • attr – Attribute to read

  • buf – Buffer to store the value read

  • len – Buffer length

  • offset – Start offset

Returns

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

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.

Parameters

  • conn – Connection object

  • attr – Attribute to read

  • buf – Buffer to store the value read

  • len – Buffer length

  • offset – Start offset

Returns

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

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. When called from the System Workqueue context this API will not wait for resources for the callback but instead return an error. The number of pending callbacks can be increased with the CONFIG_BT_CONN_TX_MAX option.

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

Parameters

  • conn – Connection object.

  • params – Notification parameters.

Returns

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

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

Notify multiple attribute value change.

This function works in the same way as bt_gatt_notify_cb.

Parameters

  • conn – Connection object.

  • num_params – Number of notification parameters.

  • params – Array of notification parameters.

Returns

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

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.

Parameters

  • conn – Connection object.

  • attr – Characteristic or Characteristic Value attribute.

  • data – Pointer to Attribute data.

  • len – Attribute value length.

Returns

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

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.

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.

Returns

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

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.

Alternatively it is possible to indicate by UUID by setting it on the parameters, when using this method the attribute if provided 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.

Parameters

  • conn – Connection object.

  • params – Indicate parameters.

Returns

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

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.

Parameters

  • conn – Connection object.

  • attr – Attribute object.

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

Returns

true if the attribute object has been subscribed.

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.

Parameters

  • conn – Connection object.

Returns

MTU in bytes

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.

Optional, use to search for an attribute with matching UUID when the attribute object pointer is not known.

const struct bt_gatt_attr *attr

Notification Attribute object.

Optional if uuid is provided, in this case it will be used as start range to search for the attribute with the given UUID.

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

Indicate Attribute UUID type.

Optional, use to search for an attribute with matching UUID when the attribute object pointer is not known.

const struct bt_gatt_attr *attr

Indicate Attribute object.

Optional if uuid is provided, in this case it will be used as start range to search for the attribute with the given UUID.

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.

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.

Param conn

Connection object.

Param attr

Attribute found, or NULL if not found.

Param params

Discovery parameters given.

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.

Param conn

Connection object.

Param err

ATT error code.

Param params

Read parameters used.

Param data

Attribute value data. NULL means read has completed.

Param length

Attribute value length.

Return

BT_GATT_ITER_CONTINUE if should continue to the next attribute.

Return

BT_GATT_ITER_STOP to stop.

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

Write callback function.

Param conn

Connection object.

Param err

ATT error code.

Param 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.

In the case of an empty notification, the data pointer will be non-NULL while the length will be 0, which is due to the special case where a data NULL pointer means unsubscribed.

Param conn

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

Param params

Subscription parameters.

Param data

Attribute value data. If NULL then subscription was removed.

Param length

Attribute value length.

Return

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

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.

enumerator BT_GATT_DISCOVER_STD_CHAR_DESC

Discover standard characteristic descriptor values. 

    Discover standard characterestic descriptor values and their
    properties.
    Supported descriptors:
     - Characteristic Extended Properties
     - Client Characteristic Configuration
     - Server Characteristic Configuration
     - Characteristic Presentation Format

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.

The Response comes in callback params->func. The callback is run from the BT RX thread. params must remain valid until start of callback.

This function will block while the ATT request queue is full, except when called from the BT RX thread, as this would cause a deadlock.

Note

Shall only be used once per connection.

Parameters

  • conn – Connection object.

  • params – Exchange MTU parameters.

Return values

  • 0 – Successfully queued request. Will call params->func on resolution.

  • -ENOMEM – ATT request queue is full and blocking would cause deadlock. Allow a pending request to resolve before retrying, or call this function outside the BT RX thread to get blocking behavior. Queue size is controlled by CONFIG_BT_L2CAP_TX_BUF_COUNT .

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.

The Response comes in callback params->func. The callback is run from the BT RX thread. params must remain valid until start of callback where iter attr is NULL or callback will return BT_GATT_ITER_STOP.

This function will block while the ATT request queue is full, except when called from the BT RX thread, as this would cause a deadlock.

Parameters

  • conn – Connection object.

  • params – Discover parameters.

Return values

  • 0 – Successfully queued request. Will call params->func on resolution.

  • -ENOMEM – ATT request queue is full and blocking would cause deadlock. Allow a pending request to resolve before retrying, or call this function outside the BT RX thread to get blocking behavior. Queue size is controlled by CONFIG_BT_L2CAP_TX_BUF_COUNT .

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.

The Response comes in callback params->func. The callback is run from the BT RX thread. params must remain valid until start of callback.

This function will block while the ATT request queue is full, except when called from the BT RX thread, as this would cause a deadlock.

Parameters

  • conn – Connection object.

  • params – Read parameters.

Return values

  • 0 – Successfully queued request. Will call params->func on resolution.

  • -ENOMEM – ATT request queue is full and blocking would cause deadlock. Allow a pending request to resolve before retrying, or call this function outside the BT RX thread to get blocking behavior. Queue size is controlled by CONFIG_BT_L2CAP_TX_BUF_COUNT .

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

Write Attribute Value by handle.

The Response comes in callback params->func. The callback is run from the BT RX thread. params must remain valid until start of callback.

This function will block while the ATT request queue is full, except when called from Bluetooth event context. When called from Bluetooth context, this function will instead instead return -ENOMEM if it would block to avoid a deadlock.

Parameters

  • conn – Connection object.

  • params – Write parameters.

Return values

  • 0 – Successfully queued request. Will call params->func on resolution.

  • -ENOMEM – ATT request queue is full and blocking would cause deadlock. Allow a pending request to resolve before retrying, or call this function outside Bluetooth event context to get blocking behavior. Queue size is controlled by CONFIG_BT_L2CAP_TX_BUF_COUNT .

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. When called from the System Workqueue context this API will not wait for resources for the callback but instead return an error. The number of pending callbacks can be increased with the CONFIG_BT_CONN_TX_MAX option.

This function will block while the ATT request queue is full, except when called from the BT RX thread, as this would cause a deadlock.

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.

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.

Return values

  • 0 – Successfully queued request.

  • -ENOMEM – ATT request queue is full and blocking would cause deadlock. Allow a pending request to resolve before retrying, or call this function outside the BT RX thread to get blocking behavior. Queue size is controlled by CONFIG_BT_L2CAP_TX_BUF_COUNT .

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

This function will block while the ATT request queue is full, except when called from the BT RX thread, as this would cause a deadlock.

Parameters

  • conn – Connection object.

  • handle – Attribute handle.

  • data – Data to be written.

  • length – Data length.

  • sign – Whether to sign data

Return values

  • 0 – Successfully queued request.

  • -ENOMEM – ATT request queue is full and blocking would cause deadlock. Allow a pending request to resolve before retrying, or call this function outside the BT RX thread to get blocking behavior. Queue size is controlled by CONFIG_BT_L2CAP_TX_BUF_COUNT .

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.

The Response comes in callback params->func. The callback is run from the BT RX thread. params must remain valid until start of callback. The Notification callback params->notify is also called from the BT RX thread.

This function will block while the ATT request queue is full, except when called from the BT RX thread, as this would cause a deadlock.

Note

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

Parameters

  • conn – Connection object.

  • params – Subscribe parameters.

Return values

  • 0 – Successfully queued request. Will call params->write on resolution.

  • -ENOMEM – ATT request queue is full and blocking would cause deadlock. Allow a pending request to resolve before retrying, or call this function outside the BT RX thread to get blocking behavior. Queue size is controlled by CONFIG_BT_L2CAP_TX_BUF_COUNT .

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.

Parameters

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

  • peer – Remote address.

  • params – Subscribe parameters.

Returns

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

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.

The Response comes in callback params->func. The callback is run from the BT RX thread.

This function will block while the ATT request queue is full, except when called from the BT RX thread, as this would cause a deadlock.

Parameters

  • conn – Connection object.

  • params – Subscribe parameters.

Return values

  • 0 – Successfully queued request. Will call params->write on resolution.

  • -ENOMEM – ATT request queue is full and blocking would cause deadlock. Allow a pending request to resolve before retrying, or call this function outside the BT RX thread to get blocking behavior. Queue size is controlled by CONFIG_BT_L2CAP_TX_BUF_COUNT .

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

Try to cancel the first pending request identified by params.

This function does not release params for reuse. The usual callbacks for the request still apply. A successful cancel simulates a BT_ATT_ERR_UNLIKELY response from the server.

This function can cancel the following request functions:

Parameters

  • conn – The connection the request was issued on.

  • params – The address params used in the request function call.

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 attr_handle

Include service attribute declaration handle

uint16_t start_handle

Included service start handle

Discover start handle

uint16_t end_handle

Included service 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 greater than 1 multiple.handles are used. If equals to 0 by_uuid is used for Read Using Characteristic UUID.

uint16_t handle

Attribute handle.

uint16_t offset

Attribute data offset.

uint16_t *handles

Attribute handles to read with Read Multiple Characteristic Values.

bool variable

If true use Read Multiple Variable Length Characteristic Values procedure. The values of the set of attributes may be of variable or unknown length. If false use Read Multiple Characteristic Values procedure. The values of the set of attributes must be of a known fixed length, with the exception of the last value that can have a variable length.

uint16_t start_handle

First requested handle number.

uint16_t end_handle

Last requested handle number.

const struct bt_uuid *uuid

2 or 16 octet 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 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

atomic_t flags[ATOMIC_BITMAP_SIZE(BT_GATT_SUBSCRIBE_NUM_FLAGS)]

Subscription flags