The
hci
node type is a Netgraph node type that implements Bluetooth Host Controller
Interface (HCI) layer as per chapter H1 of the Bluetooth Specification Book
v1.1.
INTRODUCTION TO BLUETOOTH
Bluetooth is a short-range radio link intended to replace the cable(s)
connecting portable and/or fixed electronic devices.
Bluetooth operates in the unlicensed ISM band at 2.4 GHz.
The Bluetooth protocol uses a
combination of circuit and packet switching.
Bluetooth can support an
asynchronous data channel, up to three simultaneous synchronous voice
channels, or a channel which simultaneously supports asynchronous data
and synchronous voice.
Each voice channel supports a 64 kb/s synchronous
(voice) channel in each direction.
The asynchronous channel can support
maximal 723.2 kb/s asymmetric (and still up to 57.6 kb/s in the return
direction), or 433.9 kb/s symmetric.
The Bluetooth system provides a point-to-point connection (only two
Bluetooth units involved), or a point-to-multipoint connection.
In the point-to-multipoint connection,
the channel is shared among several Bluetooth units.
Two or more units sharing the same channel form a
``piconet''
One Bluetooth unit acts as the master of the piconet, whereas the other
unit(s) acts as slave(s).
Up to seven slaves can be active in the piconet.
In addition, many more slaves can remain locked to the master in a so-called
parked state.
These parked slaves cannot be active on the channel, but remain
synchronized to the master.
Both for active and parked slaves, the channel
access is controlled by the master.
Multiple piconets with overlapping coverage areas form a
``scatternet''
Each piconet can only have a single master.
However, slaves can participate
in different piconets on a time-division multiplex basis.
In addition, a master in one piconet can be a slave in another piconet.
The piconets shall not be frequency-synchronized.
Each piconet has its own hopping channel.
Time Slots
The channel is divided into time slots, each 625 usec in length.
The time
slots are numbered according to the Bluetooth clock of the piconet master.
The slot numbering ranges from 0 to 2^27 -1 and is cyclic with a cycle length
of 2^27.
In the time slots, master and slave can transmit packets.
SCO Link
The SCO link is a symmetric, point-to-point link between the master and a
specific slave.
The SCO link reserves slots and can therefore be considered
as a circuit-switched connection between the master and the slave.
The SCO link typically supports time-bounded information like voice.
The master can
support up to three SCO links to the same slave or to different slaves.
A slave can support up to three SCO links from the same master, or two SCO
links if the links originate from different masters.
SCO packets are never retransmitted.
ACL Link
In the slots not reserved for SCO links, the master can exchange packets
with any slave on a per-slot basis.
The ACL link provides a packet-switched
connection between the master and all active slaves participating in the
piconet.
Both asynchronous and isochronous services are supported.
Between a master and a slave only a single ACL link can exist.
For most ACL packets,
packet retransmission is applied to assure data integrity.
HOST CONTROLLER INTERFACE (HCI)
The HCI provides a command interface to the baseband controller and link
manager, and access to hardware status and control registers.
This interface
provides a uniform method of accessing the Bluetooth baseband capabilities.
The HCI layer on the Host exchanges data and commands with the HCI firmware
on the Bluetooth hardware.
The Host Controller Transport Layer (i.e., physical
bus) driver provides both HCI layers with the ability to exchange information
with each other.
The Host will receive asynchronous notifications of HCI events independent
of which Host Controller Transport Layer is used.
HCI events are used for
notifying the Host when something occurs.
When the Host discovers that an
event has occurred it will then parse the received event packet to determine
which event occurred.
The next sections specify the HCI packet formats.
HCI Command Packet
#define NG_HCI_CMD_PKT 0x01
typedef struct {
u_int8_t type; /* MUST be 0x1 */
u_int16_t opcode; /* OpCode */
u_int8_t length; /* parameter(s) length in bytes */
} __attribute__ ((packed)) ng_hci_cmd_pkt_t;
The HCI command packet is used to send commands to the Host Controller
from the Host.
When the Host Controller completes most of the commands,
a Command Complete event is sent to the Host.
Some commands do not receive
a Command Complete event when they have been completed.
Instead, when the
Host Controller receives one of these commands the Host Controller sends
a Command Status event back to the Host when it has begun to execute the
command.
Later on, when the actions associated with the command have finished,
an event that is associated with the sent command will be sent by the Host
Controller to the Host.
HCI Event Packet
#define NG_HCI_EVENT_PKT 0x04
typedef struct {
u_int8_t type; /* MUST be 0x4 */
u_int8_t event; /* event */
u_int8_t length; /* parameter(s) length in bytes */
} __attribute__ ((packed)) ng_hci_event_pkt_t;
The HCI event packet is used by the Host Controller to notify the Host
when events occur.
HCI ACL Data Packet
#define NG_HCI_ACL_DATA_PKT 0x02
typedef struct {
u_int8_t type; /* MUST be 0x2 */
u_int16_t con_handle; /* connection handle + PB + BC flags */
u_int16_t length; /* payload length in bytes */
} __attribute__ ((packed)) ng_hci_acldata_pkt_t;
HCI ACL data packets are used to exchange ACL data between the Host and
Host Controller.
HCI SCO data packets are used to exchange SCO data between the Host and
Host Controller.
HCI INITIALIZATION
On initialization, HCI control application must issue the following HCI
commands (in any order).
Read_BD_ADDR
To obtain BD_ADDR of the Bluetooth unit.
Read_Local_Supported_Features
To obtain the list of features supported by Bluetooth unit.
Read_Buffer_Size
To determine the maximum size of HCI ACL and SCO HCI data packets (excluding
header) that can be sent from the Host to the Host Controller.
There are also
two additional return parameters that specify the total number of HCI ACL and
SCO data packets that the Host Controller can have waiting for transmission in
its buffers.
As soon as HCI initialization has been successfully performed, HCI control
application must turn on
``inited''
bit for the node.
Once HCI node has been initialized all upstream hooks
will receive a
NGM_HCI_NODE_UP
Netgraph message defined as follows.
HCI layer performs flow control on baseband connection basis (i.e., ACL and
SCO link).
Each baseband connection has
``connection handle''
and queue of outgoing data packets.
Upper layers protocols are allowed to
send up to
( num_pkts
-
pending
packets at one time.
HCI layer will send
NGM_HCI_SYNC_CON_QUEUE
Netgraph messages to inform upper layers about current queue state for each
connection handle.
The
NGM_HCI_SYNC_CON_QUEUE
Netgraph message is defined as follows.
Bluetooth Host Controller Transport Layer hook.
Single HCI packet contained in single
Vt mbuf
structure.
acl
Upper layer protocol/node is connected to the hook.
Single HCI ACL data packet contained in single
Vt mbuf
structure.
sco
Upper layer protocol/node is connected to the hook.
Single HCI SCO data packet contained in single
Vt mbuf
structure.
raw
Raw hook.
Every HCI frame (including HCI command frame) that goes in
or out will be delivered to the hook.
Usually the Bluetooth raw HCI socket layer is connected to the hook.
Single HCI frame contained in single
Vt mbuf
structure.
BLUETOOTH UPPER LAYER PROTOCOLS INTERFACE (LP CONTROL MESSAGES)
NGM_HCI_LP_CON_REQ
Requests the lower protocol to create a connection.
If a physical link
to the remote device does not exist, this message must be sent to the lower
protocol (baseband) to establish the physical connection.
NGM_HCI_LP_DISCON_REQ
Requests the lower protocol (baseband) to terminate a connection.
NGM_HCI_LP_CON_CFM
Confirms success or failure of the
NGM_HCI_LP_CON_REQ
request to establish a lower layer (baseband) connection.
This includes passing the authentication challenge if authentication is
required to establish the physical link.
NGM_HCI_LP_CON_IND
Indicates the lower protocol (baseband) has successfully established
incoming connection.
NGM_HCI_LP_CON_RSP
A response accepting or rejecting the previous connection indication request.
NGM_HCI_LP_DISCON_IND
Indicates the lower protocol (baseband) has terminated connection.
This could be a response to
NGM_HCI_LP_DISCON_REQ
or a timeout event.
NGM_HCI_LP_QOS_REQ
Requests the lower protocol (baseband) to accommodate a particular QoS
parameter set.
NGM_HCI_LP_QOS_CFM
Confirms success or failure of the request for a given quality of service.
NGM_HCI_LP_QOS_IND
Indicates the lower protocol (baseband) has detected a violation of the QoS
agreement.
NETGRAPH CONTROL MESSAGES
This node type supports the generic control messages, plus the following:
NGM_HCI_NODE_GET_STATE
Returns current state for the node.
NGM_HCI_NODE_INIT
Turn on
``inited''
bit for the node.
NGM_HCI_NODE_GET_DEBUG
Returns an integer containing the current debug level for the node.
NGM_HCI_NODE_SET_DEBUG
This command takes an integer argument and sets current debug level
for the node.
NGM_HCI_NODE_GET_BUFFER
Returns current state of data buffers.
NGM_HCI_NODE_GET_BDADDR
Returns BD_ADDR as cached in the node.
NGM_HCI_NODE_GET_FEATURES
Returns the list of features supported by hardware (as cached by the node).
NGM_HCI_NODE_GET_NEIGHBOR_CACHE
Returns content of the neighbor cache.
NGM_HCI_NODE_FLUSH_NEIGHBOR_CACHE
Remove all neighbor cache entries.
NGM_HCI_NODE_GET_CON_LIST
Returns list of active baseband connections (i.e., ACL and SCO links).
NGM_HCI_NODE_GET_STAT
Returns various statistic counters.
NGM_HCI_NODE_RESET_STAT
Resets all statistic counters to zero.
NGM_HCI_NODE_SET_LINK_POLICY_SETTINGS_MASK
Sets current link policy settings mask.
After the new ACL connection is
created the HCI node will try set link policy for the ACL connection.
By default, every supported Link Manager (LM) mode will be enabled.
User can
override this by setting link policy settings mask which specifies LM
modes to be enabled.
NGM_HCI_NODE_GET_LINK_POLICY_SETTINGS_MASK
Returns current link policy settings mask.
NGM_HCI_NODE_SET_PACKET_MASK
Sets current packet mask.
When new baseband (ACL or SCO) connection is
created the HCI node will specify every packet type supported by the device.
User can override this by setting packet mask which specifies packet types
to be used for new baseband connections.
NGM_HCI_NODE_GET_PACKET_MASK
Returns current packet mask.
NGM_HCI_NODE_SET_ROLE_SWITCH
Sets the value of the role switch.
Role switch is enabled when this value is not zero.
This is the default state.
Note that actual role switch at Bluetooth link level will only be performed if
hardware supports role switch and it was enabled.
NGM_HCI_NODE_GET_ROLE_SWITCH
Returns the value of the role switch for the node.
SHUTDOWN
This node shuts down upon receipt of a
NGM_SHUTDOWN
control message, or
when all hooks have been disconnected.
