Image Processing Reference
In-Depth Information
A
sporadic
signalisonewhichiswrittenbytheapplicationinresponsetosomeevent(e.g.,a
button press).
A
periodic
signal is one which is written by the application at regular intervals.
he
latency
of a signal is the time from notional generation to being available to Volcano (for a
published signal), or from being made available to the application by Volcano to notional consump-
tion (for a subscribed signal). Note that immediate signals (those in immediate frames) include time
taken to move frames to/from the network in these latencies.
he
min_interval
has different interpretation for published and for subscribed signals.
For a published signal, it is the minimum time between any pair of write calls to the signal (this
allows, e.g., the calculation of the maximum rate at which the signal could cause a sporadic frame
carrying it to be transmitted).
For a subscribed signal, it is the minimum acceptable time between arrivals of the signal. his is
optional—it is intended to be used if the processing associated with the signal is triggered by arrival
of a new value, rather than periodic. In such a case, it provides a constraint that the signal should not
be connected to published signal with a faster rate.
he
max_interval
has different interpretation for published and for subscribed signals.
For a published signal, the interesting timing information is already captured by min_interval and
publish latency.
For a subscribed signal it is the maximum interval between “notional consumptions” of the signal
(i.e., it can be used to determine that signal values are sampled quickly enough that none will be
missed).
he
max_age
of a signal is the maximum acceptable age of a signal at notional consumption,
measured from notional generation. his value is meaningful for subscribed signals.
In addition to the signal timing properties described above, the Volcano fixed configuration file
provides syntax to capture the following additional timing-related information:
•
Volcano processing period
•
Volcano jitter time
he
volcano processing period
defines the nominal interval between successive v_input() calls on
the ECU, and also between successive v_output() calls (i.e., the rates of the calls are the same, but
v_input() and v_output() are not assumed to “become due” at the same instant). For example, if the
volcano processing period is ms then each v_output() call becomes due ms after the previous one
becomes due.
he
volcano jitter
defines the time by which the actual call may lag behind the time at which it
became due. Note that becomes due refers to the start of the call, and jitter refers to completion of
the call.
19.15 Volcano Network Architect
To manage increasing complexity in electrical architectures, a structured development approach is
believed essential to assure correctness by design. Volcano automotive group has developed a network
design tool, volcano network architect (VNA), to support a development process, based on strict
systems engineering principles. Gatewaying of signals between different networks is automatically
handled by the VNA tool and the accompanying embedded software.
The tool supports partitioning of responsibilities into different roles such as system integrator
and function owner. Third party tools may be used for functional modeling. These models can be
imported into VNA.
