Embedded Software for SoC - Grupo de Mecatrônica EESC/USP

Exploring SW Performance 103
The channel may use a subsequent protocol with the slave to play the pre
and post transactions.
In the case of the AMBA bus, the pre() and post() are respectively corresponding
to management of the write transactions giving the in parameters
of the operations and the read transactions to retrieve the out parameters of
the operations.
Figure 8-6 shows how the pattern has been applied for the AMBA-bus. The
write_txs() and read_txs give the user provided data describing the transaction
configuration to the channel. These data notably contains the number of
bytes to be transmitted, and the width of the words. They do no contain the
actual data transmitted to the slave, these are given by the parameters on the
function call.
These are macro transactions are then decomposed accordingly to the bus
specification (burst are bound to 1 Ko address space) and the arbitration policy
selected for the bus.
The bus notifies the slave access that some bytes must be written to its
buffer. The slave access will provide a delayed answer to the bus write transaction
query. This is the slave access that count the number of cycles used to
complete the bus transaction.
The slave access can give several replies accordingly to the amba bus
specifications: