NG_HCI(4) BSD Kernel Interfaces Manual NG_HCI(4)NAMEng_hci — Netgraph node type that is also a Bluetooth Host Controller
Interface (HCI) layer
SYNOPSIS
#include <sys/types.h>
#include <netgraph/bluetooth/include/ng_hci.h>
DESCRIPTION
The hci node type is a Netgraph node type that implements Bluetooth Host
Controller Interface (HCI) layer as per chapter H1 of the Bluetooth Spec‐
ification 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 Blue‐
tooth units involved), or a point-to-multipoint connection. In the
point-to-multipoint connection, the channel is shared among several Blue‐
tooth 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 mas‐
ter 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 partici‐
pate in different piconets on a time-division multiplex basis. In addi‐
tion, 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 consid‐
ered 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 differ‐
ent slaves. A slave can support up to three SCO links from the same mas‐
ter, 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 participat‐
ing in the piconet. Both asynchronous and isochronous services are sup‐
ported. 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 indepen‐
dent of which Host Controller Transport Layer is used. HCI events are
used for notifying the Host when something occurs. When the Host discov‐
ers 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 Con‐
troller 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 Packet
#define NG_HCI_SCO_DATA_PKT 0x03
typedef struct {
u_int8_t type; /* MUST be 0x3 */
u_int16_t con_handle; /* connection handle + reserved bits */
u_int8_t length; /* payload length in bytes */
} __attribute__ ((packed)) ng_hci_scodata_pkt_t;
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 con‐
trol 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.
#define NGM_HCI_NODE_UP 112 /* HCI -> Upper */
typedef struct {
u_int16_t pkt_size; /* max. ACL/SCO packet size (w/o hdr) */
u_int16_t num_pkts; /* ACL/SCO packet queue size */
u_int16_t reserved; /* place holder */
bdaddr_t bdaddr; /* bdaddr */
} ng_hci_node_up_ep;
HCI FLOW CONTROL
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.
#define NGM_HCI_SYNC_CON_QUEUE 113 /* HCI -> Upper */
typedef struct {
u_int16_t con_handle; /* connection handle */
u_int16_t completed; /* number of completed packets */
} ng_hci_sync_con_queue_ep;
HOOKS
This node type supports the following hooks:
drv Bluetooth Host Controller Transport Layer hook. Single HCI
packet contained in single mbuf structure.
acl Upper layer protocol/node is connected to the hook. Single HCI
ACL data packet contained in single mbuf structure.
sco Upper layer protocol/node is connected to the hook. Single HCI
SCO data packet contained in single 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 Blue‐
tooth raw HCI socket layer is connected to the hook. Single HCI
frame contained in single 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 physi‐
cal link to the remote device does not exist, this message must
be sent to the lower protocol (baseband) to establish the physi‐
cal 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 estab‐
lished incoming connection.
NGM_HCI_LP_CON_RSP
A response accepting or rejecting the previous connection indica‐
tion request.
NGM_HCI_LP_DISCON_IND
Indicates the lower protocol (baseband) has terminated connec‐
tion. 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 particu‐
lar 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 con‐
nection 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) connec‐
tion is created the HCI node will specify every packet type sup‐
ported 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.
SEE ALSOnetgraph(4), hccontrol(8), ngctl(8)HISTORY
The hci node type was implemented in FreeBSD 5.0.
AUTHORS
Maksim Yevmenkin ⟨m_evmenkin@yahoo.com⟩
BUGS
Most likely. Please report if found.
BSD June 25, 2002 BSD
