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of resources and complex scheduling so will probably be rare at least in early implementation s
of bluetooth le audio devices in most cases utilising cached configurations to allow simple
transitions is likely to provide an easier solution
section ascs the audio stream control service
figure an example of exposed ase states for multipl e client s
figure shows how these principles work it shows how an acceptor with three ases
might expose its instantiated states for three different client s curren tly only client a has
established stream s with the ases which have handles of x x and x if
client a reads the three ases it will learn that all three are in the streaming state
if client b were to read the same handles it would be inf ormed that all three are idle note
that the aseids for client b may be different as the acceptor allocates and maintains a
different namespace for each client
finally when client c reads them it will be told that they are in the codec configured s tate
this will normally be because client c h as had a previous set of streams enabled and when
they were released it asked that the acceptor kept the ases in the codec configured state to
speed up the connection next time client c wanted to establish a stream in this state the
codec configuration is exposed so that client c can see whether it needs to perform a
reconfiguration before moving the ases to the qos configured state in other states the
codec configura tion information is not exposed
an acceptor must expose at least one ase for every audio stream that it can support if it
supports multi ple bl uetooth le audio channels in either direction it must support at least
one ase for each of those audio channel s regardless of whether it uses all of them if it
supports multiplexing the number of ases in each direction must be equal or greater than
the number of audio location bits set to b for that direction divided by the highest number
of audio channels set in the audiochannelcounts ltv bap if an acceptor can
support simultaneous audio streams from two or more clients at the same time it needs to
provide an ase for each audio stream put more simply the acceptor has to support
everything it claims can be thrown at it with at least one ase for each audio stream
chapter setting up unicast audio streams
it might feel as though there is a conflict between the global scope of the pac record and the
more limited configurations of an ase but they have dif ferent purposes and scope to
understand the relationship between a pac record and an ase it might be helpful to consider
an analogy so well resort to food again if you think of a restaurant the published audio
capabilities are like a full list of ingredients that are in the kitchen the ases are the individual
dishes which only use a subset of those ingredients the restaurants expectation is that
people choose the dishes off the menu because theyve normally been developed to suit the
use cas e which in the restaurants case may be breakfast lunch afternoon tea or dinner
however sometimes the customer might ask for something different if a diner comes in and
asks for a burger with chips mash toast pasta and custard which i hope is not an item on
any menu bap takes the view that the customer is always right and allows it to limit those
occasions it may be helpful to expose individual pac records which correspond to the use
cases supported by the top level profiles in this res taurant analogy that would be different
menus for different times of day
moving around the state machine involves an interplay of bap issuing a command and ascs
responding rather than going into detail about ascs in isolation its more useful to look at
the actual process of interactions in setting up a stream
bap the basic audio profile
ascs describes the states of an ase but not the procedures to use them as its a service
which resides on a server it is a statement of the current state of each audio stream endpoint
on an acceptor to perform the transitions that move us through the ase state machine to
configure an ase and enable a cis we need to move to the basic audio profile which defines
the client initiator behaviour bap defines these procedures for both unicast and broadcast
and cap bundl es them together in this chapter well confine our selves to the unicast
procedures in the next chapter well do the same for broadcast
setting up a source ase is essentially the same process but with one extra state which well
cover at the end
moving through the ase state machine
moving through th e ase state machine uses a standard process the initiator sends a
command to the acceptors ase control point characteristic specifying the control operation
to be performed ie which state it wants the ases to transition to or which state need s to
be updated the command specifies which ase or ases the command is being applied to
and the parameters for that particular state transition
the command takes the form shown in table and includes a set of operation specific
parameters for each state well look at each set of operation specific parameters as we go
through the state machine configuration process
section bap the basic audio profile
field size octets description
opcode control point operation for the next
state or update as shown in table
number of ases total number of ases included in this
operation
aseidi the ids of those ases
operation specific
parameters varies a list of parameters for each of the i
ases
table basic structure of ase control point command operations for an initiator
at each stage the initiator is made aware of the capabilities of the acceptor as long as it
does not request features outside those provided by the acceptor the initiator can expect the
acceptor to honour all of its ase control point commands values onc e it has received each
ase control point command the acceptor responds with an ase control point
characteristic notification indicating success or otherwise for each of the i number of
aseids which were contained in the comma nd as shown in table
field size octets description
number of ases total number of ases included in this operation
aseidi the ids of those ases
responsecodei x if successful otherwise an error response
code from table of ascs
reasoni an extended reason code from table of ascs
x indicates success other codes provide
reasons where the operation has failed
table ase control point characteristic format as notified to its client
if any of them are rejected or have errors there is a comprehensive set of error responses to
inform the initiator so that it can try again note that all of these operations are fo r arrays of
i ases they can be sent as individual commands for each ase but its more efficient to
include all of the aseids for each acceptor in one operation
assuming there are no issues the acceptor then proceeds to update the state of all of it s sink
ase and source ase characteristics with the values that the initiator provided in its ase
control point command if that results in a change to any ase the acceptor will notify the
new value for each ase that has changed