Channel Control
Bluetooth controller operates in two major states: Standby and Connection
. There are seven substates which are used to add slaves or make connections
in the piconet. These are page, page scan, inquiry, inquiry scan, master
response, slave response and inquiry response .
Connection Setup
The Standby state is the default low power state in the Bluetooth unit.
Only the native clock is running and there is no interaction with any
device whatsoever. In the Connection state, the master and slave can exchange
packet , using the master's channel access code and the master's Bluetooth
clock.
The inquiry procedure enables a device to discover which devices are in
range, and determine the addresses and clocks for the devices.
With the paging procedure, an actual connection can be established. The
paging procedure typically follows the inquiry procedure. Only the Bluetooth
device address is required to set up a connection. Knowledge about the
clock will accelerate the setup procedure. A unit that establishes a connection
will carry out a page procedure and will automatically be the master of
the connection. The procedure occurs as follows:
The Connection state starts with a POLL packet sent by the master to verify that slave has switched to the master's timing and channel frequency hopping. The slave can respond with any type of packet.
Connection Modes
A Bluetooth device in the Connection state can be in any of the four following
modes: Active, Hold, Sniff and Park mode.
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Active Mode: In the active mode, the Bluetooth unit actively participates on the channel. The master schedules the transmission based on traffic demands to and from the different slaves. In addition, it supports regular transmissions to keep slaves synchronized to the channel. Active slaves listen in the master-to-slave slots for packets. If an active slave is not addressed, it may sleep until the next new master transmission.
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Sniff Mode: Devices synchronized to a piconet can enter power-saving modes in which device activity is lowered. In the SNIFF mode, a slave device listens to the piconet at reduced rate, thus reducing its duty cycle. The SNIFF interval is programmable and depends on the application. It has the highest duty cycle (least power efficient ) of all 3 power saving modes (sniff, hold & park).
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Hold Mode: Devices synchronized to a piconet can enter power-saving modes in which device activity is lowered. The master unit can put slave units into HOLD mode, where only an internal timer is running. Slave units can also demand to be put into HOLD mode. Data transfer restarts instantly when units transition out of HOLD mode.
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Park Mode: In the PARK mode, a device is still synchronized to the piconet but does not participate in the traffic. Parked devices have given up their MAC address and occasional listen to the traffic of the master to re-synchronize and check on broadcast messages.
