l2cap.h File Reference

Bluetooth L2CAP Layer. More...

#include <stdint.h>
#include "FreeRTOS.h"
#include "semphr.h"

Go to the source code of this file.

Classes
struct	l2cap_signal_t
struct	l2cap_channel_t
struct	l2cap_device_t

Macros
#define	L2CAP_SIGNAL_CHANNEL_BUFFER_SIZE   256
#define	L2CAP_CHANNEL_SIGNALS   0x0001
#define	L2CAP_DEFAULT_MTU   185
#define	L2CAP_DEFAULT_FLUSH_TIMEOUT   0xFFFF

Typedefs
typedef void(*	l2cap_channel_event_t) (void *channel, void *user)

Functions
int	l2cap_initialize ()
	Initalized L2CAP.
void	l2cap_signal_close ()
	Begins closing out of L2CAP.
void	l2cap_close ()
	Closes out of L2CAP.
int	l2cap_open_device (l2cap_device_t *device_handle, uint16_t hci_device_handle, const uint8_t *mac_address)
	Opens a L2CAP Connections.
void	l2cap_close_device (l2cap_device_t *device_handle)
	Closes a L2CAP Connection.
int	l2cap_open_channel (l2cap_device_t *device_handle, l2cap_channel_t *channel, uint16_t protocol_id, uint8_t *rx_buffer, int rx_buffer_size)
	Opens a L2CAP Channel.
void	l2cap_close_channel (l2cap_channel_t *channel)
	Closes a L2CAP Channel.
int	l2cap_send_channel (l2cap_channel_t *channel, const void *data, uint16_t size)
	Sends data over a L2CAP Channel.
int	l2cap_receive_channel (l2cap_channel_t *channel, void *data, uint16_t size)
	Receives from a L2CAP Channel.
void	l2cap_set_channel_receive_event (l2cap_channel_t *channel, l2cap_channel_event_t event, void *param)
	Sets the L2CAP on packet receive event.

Detailed Description

Bluetooth L2CAP Layer.

L2CAP is a higher level ontop of HCI's ACI packets used to send and receive data from devices.

Its in charge of multiplexing data and reassembling/disassembling packets.

Author

Samuel Fitzsimons (rainbain)

Date

2025

Function Documentation

l2cap_close()

void l2cap_close ( )

extern

Closes out of L2CAP.

Must come after l2cap_signal_close and the HCI is closed. Will wait for the task to exit.

l2cap_close_channel()

void l2cap_close_channel ( l2cap_channel_t * channel )

extern

Closes a L2CAP Channel.

Closes a channel and frees its resources.

This will automatically be done for any remaining open channels when calling l2cap_close_device.

Parameters

channel

Channel to close.

l2cap_close_device()

void l2cap_close_device ( l2cap_device_t * device_handle )

extern

Closes a L2CAP Connection.

Frees a L2CAP device and closes and frees all associated open channels.

Parameters

device_handle

L2CAP device to close

l2cap_initialize()

int l2cap_initialize ( )

extern

Initalized L2CAP.

Its recommended this is called after hci_initialize but before working with any bluetooth devices.

This allows you to use L2CAP once a connection has been established.

Returns

Negative if Error

l2cap_open_channel()

int l2cap_open_channel ( l2cap_device_t * device_handle, l2cap_channel_t * channel, uint16_t protocol_id, uint8_t * rx_buffer, int rx_buffer_size )

extern

Opens a L2CAP Channel.

Once a device is open, channels can be opened and closed. Channels are much like sockets, and each one has its own protocol.

By default, the signal channel is already open and used by L2CAP.

Parameters

device_handle	L2CAP device to open the channel on
channel	Channel data structure to write into
protocol_id	Protocol of the channel. Like the socket.
rx_buffer	The receiving buffer for the channel.
rx_buffer_size	Size of the receiving buffer. Must be a power of 2.

Returns

Negative if Error.

l2cap_open_device()

int l2cap_open_device ( l2cap_device_t * device_handle, uint16_t hci_device_handle, const uint8_t * mac_address )

extern

Opens a L2CAP Connections.

Sets up L2CAP to communicate with a device. This sets up the default signal channel L2CAP uses, and adds the device to L2CAPS list of active devices.

Parameters

device_handle	L2CAP Device Handle To Create
hci_device_handle	Device handle created by hci_create_connection
mac_address	MAC address of the device. Used to prevent duplicate connections.

Returns

Negative if Error.

l2cap_receive_channel()

int l2cap_receive_channel ( l2cap_channel_t * channel, void * data, uint16_t size )

extern

Receives from a L2CAP Channel.

Receives data from the internal buffer specified when creating the channel.

The buffer is treated as a FIFO and can hold multiple packets. In the event of an overflow, packet truncation and packet drops are logged and this will just return truncated or 0 byte packets.

Packets should never be truly lost, just that you will have saved up a bunch of 0 byte packets.

Will error on incomplete FIFO fragments.

Parameters

channel	Channel to talk to
data	Data Buffer
size	Size of buffer. Up to 65535.

Returns

Total bytes read (even if they did not fit into buffer). Negative if error.

l2cap_send_channel()

int l2cap_send_channel ( l2cap_channel_t * channel, const void * data, uint16_t size )

extern

Sends data over a L2CAP Channel.

Sends a buffer over a L2CAP channel. Channels in L2CAP can be thought of as a lot like sockets. One device can run multiple protocols, and we expect to see specific protocols on specific channels.

Parameters

channel	Channel to talk to
data	Data Buffer
size	Size of data. Up to 65535.

Returns

Negative if Error

l2cap_set_channel_receive_event()

void l2cap_set_channel_receive_event ( l2cap_channel_t * channel, l2cap_channel_event_t event, void * param )

extern

Sets the L2CAP on packet receive event.

When a packet is received on a channel, this event will be called to receive it if you please.

Parameters

channel	Channel to set it in
event	Event Handler
param	Parameter passed to event.

l2cap_signal_close()

void l2cap_signal_close ( )

extern

Begins closing out of L2CAP.

I don't currently have a good way to cancel the blocking ACL read from it, so this will signal the thread to begin exiting. Once HCI is closed, it will actually exist.