GATT Latency Client

You can use the Latency Client to interact with a connected peer that is running the Latency service with the GATT Latency Service. It writes data to the Latency characteristic and waits for a response to count the time spent of a GATT Write operation.

Latency Characteristic

To request latency data from the Latency Characteristic, use the bt_latency_request() function. The request sending procedure is asynchronous, so the request data to be sent must remain valid until a dedicated callback notifies you that the write request has been completed.

API documentation

Header file: include/bluetooth/services/latency_client.h
Source file: subsys/bluetooth/services/latency_client.c
group bt_latency_c

API for the Bluetooth LE GATT Latency Client.

Functions

int bt_latency_client_init(struct bt_latency_client *latency, const struct bt_latency_client_cb *cb)

Initialize the GATT latency client.

Parameters:

  • latency – [in] Latency client instance.

  • cb – [in] Callbacks.

Return values:

  • 0 – If the operation was successful. Otherwise, a negative error code is returned.

  • (-EINVAL) – Special error code used when the input parameters are invalid.

  • (-EALREADY) – Special error code used when the latency client has been initialed.

int bt_latency_handles_assign(struct bt_gatt_dm *dm, struct bt_latency_client *latency)

Assign handles to the latency client instance.

This function should be called when a link with a peer has been established, to associate the link to this instance of the module. This makes it possible to handle several links and associate each link to a particular instance of this module. The GATT attribute handles are provided by the GATT Discovery Manager.

Parameters:

  • dm – [in] Discovery object.

  • latency – [inout] Latency client instance.

Return values:

  • 0 – If the operation was successful. Otherwise, a negative error code is returned.

  • (-ENOTSUP) – Special error code used when the UUID of the service does not match the expected UUID.

  • (-EINVAL) – Special error code used when the UUID characteristic or value descriptor not found.

int bt_latency_request(struct bt_latency_client *latency, const void *data, uint16_t len)

Write data to the server.

Parameters:

  • latency – [in] Latency client instance.

  • data – [in] Data.

  • len – [in] Data length.

Return values:

  • 0 – If the operation was successful. Otherwise, a negative error code is returned.

  • (-EALREADY) – Special error code used when the asynchronous request is waiting for a response.

struct bt_latency_client_cb
#include <latency_client.h>

Latency client callback structure.

Public Members

void (*latency_response)(const void *buf, uint16_t len)

Latency received callback.

This function is called when a GATT write response has been received by the Latency characteristic.

It is mandatory for an application to handle the write response when measuring the latency.

Param buf:

[in] Latency data.

Param len:

[in] Latency data length.

struct bt_latency_client
#include <latency_client.h>

Latency client structure.

Public Members

uint16_t handle

Characteristic handle.

struct bt_gatt_write_params latency_params

Latency parameter.

struct bt_conn *conn

Connection object.

atomic_t state

Internal state.