Embedded Software for SoC - Grupo de Mecatrônica EESC/USP

76 Chapter 6
may share data. Event handlers are non-blocking. As a result‚ blocking behaviors
are explicitly specified by states. To remove a blocking operation from
an event handler‚ the specification writer can restructure the state machine
by splitting the handler at the operation and inserting a new state. Thus‚ we
describe synchronization behaviors declaratively using states‚ rather than procedurally‚
which enables better checking. Specifically‚ interrupt processing is
modeled as a couple of hardware event handlers.
4.3. Control function specification
A core function is responsible for providing the device services to the upper
layers of software. As illustrated in Figure 6-1‚ core functions are responsible
for managing data accesses and manipulating device states. Data accesses
follow well-defined semantics‚ which specify‚ for example‚ that a block of
data has to be transferred between the processor and device. Control functions
are responsible for changing the control state of the device according to the
state machines. As illustrated in the lower part of Figure 6-5‚ a core control
function has an input event and a final state set. It accomplishes specific
functions by triggering a sequence of transitions. Because a transition may
emit multiple output events‚ multiple transitions can be enabled at one time.