Image Processing Reference
In-Depth Information
Frame
processing
period
T
V
T
V
T
V
E
L
Occurrence of
periodic event
that initiates
Volc ano
processing calls
Best-case
execution time of
v_ output
call
Execution of
other
computation
Completion
v_ output
call
Worst-case
execution time of
v_ output
call
FIGURE .
Output jitter.
In the figure,
E
marks the earliest completion time of the v_output() call, and
L
marks the latest
completion time, relative to the start of the cycle. he output_jitter is therefore
L
−
E
.heinput_jitter
is measured according to the same principles.
If a single-thread system is used, without interrupts, the calculation of the input_jitter and out-
put_jitter is straightforward: the earliest time is the best-case execution time of all the calls in the
cycle (including the v_output() call), and the latest time is the worst-case execution time of all the
calls. he situation is more complex if interrupts can occur or the system consists of multiple tasks,
since the latest time must take into account preemption from interrupts and other tasks.
19.14 Capture of Timing Constraints
The declaration of a signal in a Volcano fixed configuration file provides syntax to capture the
following timing-related information:
Whether a signals is
state
or
state change—(info_type)
Whether a signals is
sporadic
or
periodic—(generation_type)
he
latency
.
he
min_interval
.
he
max_interval
.
he
max_age
.
Thefirst two (together with whether the signal is published or subscribed to) provide signal properties
which determine the “kind” of the signal.
A
state
signal carries a value which completely describes the signaled property (e.g., the current
position of a switch). A subscriber to such a signal need only observe the signal value when the infor-
mation is required for the subscribers purposes (e.g., signal values can be “missed” without affecting
the usefulness of later values).
A
state change
signal carries a value which must always be observed in order to be meaningful
(e.g., distance traveled since last signal value). A subscriber must observe every signal value.
