Logical Link Control and Adaptation Protocol (L2CAP)
L2CAP layer enables connection-oriented channels which can be enable with the
configuration option: CONFIG_BT_L2CAP_DYNAMIC_CHANNEL. This channels
support segmentation and reassembly transparently, they also support credit
based flow control making it suitable for data streams.
Channels instances are represented by the bt_l2cap_chan struct which
contains the callbacks in the bt_l2cap_chan_ops struct to inform
when the channel has been connected, disconnected or when the encryption has
changed.
In addition to that it also contains the recv callback which is called
whenever an incoming data has been received. Data received this way can be
marked as processed by returning 0 or using
bt_l2cap_chan_recv_complete() API if processing is asynchronous.
Note
The recv callback is called directly from RX Thread thus it is not
recommended to block for long periods of time.
For sending data the bt_l2cap_chan_send() API can be used noting that
it may block if no credits are available, and resuming as soon as more credits
are available.
Servers can be registered using bt_l2cap_server_register() API passing
the bt_l2cap_server struct which informs what psm it should
listen to, the required security level sec_level, and the callback
accept which is called to authorize incoming connection requests and
allocate channel instances.
Client channels can be initiated with use of bt_l2cap_chan_connect()
API and can be disconnected with the bt_l2cap_chan_disconnect() API.
Note that the later can also disconnect channel instances created by servers.