Embedded Software for SoC - Grupo de Mecatrônica EESC/USP

Evaluation of Applying SpecC to the Integrated Design Method 143
block in trap, a behavior needs to be described so the dummy behavior which
does nothing is used.
Three kinds of channels are used for each description of the transmitter
part and the receiver part. Since data is passed one byte at a time between
tx_byte and tx_bit, and rx_byte and rx_bit, raw data is directly copied between
these behaviors. However, pointers are used to pass IP packet and PPP packet
between the application and tx_ppp, tx_ppp and tx_byte to avoid the data
copy. The SpecC code of a byte channel which delivers 1-byte data is shown
in Figure 11-4. PPP packet channels (ppp_packet_channel) and IP packet
channels (ip_packet_channel) also use same structure as a byte channel except
for the type of data to be delivered.
To confirm the SIO system description, the serial lines of the transmitter
and the receiver are connected (loop back) and simulation is performed using
the test bench where tx_ppp transmits an IP packet to rx_ppp. SpecC reference
compiler (SCRC 1.1) is used for the simulation environment. The results
of the simulation show that the SIO system description operates correctly.
Despite the redundancy in the description of the reset function, the SIO
system has been described using parallelism and synchronization and communication
statements in SpecC. Thus, SpecC satisfies evaluation point (1)
described in section 3.
4.1. SpecC description guidelines
In the SIO system description, system functions with equal execution timing
are included in the same behavior. The system functions are grouped into
behaviors according to their activation frequencies. The point where the
execution frequency changes is considered as a suitable point for software and
hardware partitioning so the behaviors in Figure 11-3 are arranged according
their activation frequency, with the right most behavior having the highest
frequency.
The main purpose of introducing channels to SpecC is to make the functional
descriptions independent from the description of synchronization and
communication by collecting synchronization and communication mechanism
to a channel. In the SpecC description of the SIO system, the descriptiveness
and readability of the behavior has improved since the behavior contains only
its functionality. Describing the behaviors that needs to communicate with the
upper and the lower layer, like tx_ppp and tx_byte, without using channels is
difficult. Thus, synchronization and communication mechanism should be
collected and described in a channel where possible. Collecting synchronization
and communication functionalities to a channel also makes the conversion
of a software from a SpecC description efficient. This is further described
in Section 5.