Embedded Software for SoC - Grupo de Mecatrônica EESC/USP

102 Chapter 8
the slave access of a bus channel as show on Figure 8-4. These compositions
can be the beginning of a methodology to refine the communication of a
system and progressively going from a purely functional model to an architectural
timed model. A first step would be to detach some functions of the
sequential algorithm into modules that prefigures the architecture. Then
regarding the iteration on the data, between the functions, one may start ahead
the detached function as soon as it has enough data to start with, for example
a subset of a picture. This is quite the same idea of setting a pipeline communication,
so one may then prepare a communication through a FIFO channel
to synchronize the execution flow of the detached functions. Note that the
FIFO can also store control so far these a operation calls which are stacked.
At this stage we a system level model very similar to what we can have with
SDL. We can introduce timing at this stage to analyze the parallelism of the
all system. Then one may decide the partitioning of the system and thus share
the communication resources. Hence a bus can refine the FIFO communications,
some data passing can be referring a shared memory. This is generally
the impact of hardware level resource sharing which is ignored by the other
specification languages which stops their analysis at the FIFO level.
2.1.3. Dynamic pattern
The Figure 8.5 shows how the protocol between the channel and its master
and slave accesses is played.
A slave registers, at the end of elaboration phase, its provided operations
to the channel through the slave access. These operations are identified with
a key made of an address, and an optional qualifier, if the address is overloaded
by the slave.
Then a master can initiate a slave operation by invocating the sibling
operation of its master access. The master access retrieves first the operation
in the decoding step and then notify the channel to execute the pre-transactions,
before the channel allows it to effectively reach the slave operation.
Once the guarded operation is done, the master access notifies the posttransaction
transactions.