Image Processing Reference
In-Depth Information
Volcano also provides a very low latency communication mechanism in the form of the
immedi-
ate frame API
. This is a “view” of frames on the network, which allows transmission and reception
from/to the Volcano domain without the normal Volcano input/output latencies, or mutual exclu-
sion requirements with the v_input() and v_output() calls. here are two communication calls in the
immediate signal API: v_imf_rx() and v_imf_tx().
The v_imf_tx() call copies values of immediate signals into a frame and places the frame in the
appropriate CAN controller for transmission. The v_imf_rx() takes a received frame containing
immediate signals and makes the signal values available to read calls.
A third call v_imf_queued() allows the user to see if an immediate frame has really been sent on
the network.
The controller calls allow the application to initialize, connect, and disconnect from networks, and
to place the controllers into “sleep” mode among others.
19.10 Volcano Resource Information
The ambition of the Volcano concept is to provide a fully predictable communications solution.
In order to achieve this, the resource usage of the Volcano embedded part has to be determined.
Resources of special interest are memory and execution time.
19.11 Execution Time of Volcano Processing Calls
In order to bound processing time, a “budget” for the v_input() call, i.e., the maximum number of
frames that will be processed by a single call to v_input(), has to be established. A corresponding
processfortransmittedframesappliesaswell.
19.12 Timing Model
he Volcano timing model covers end-to-end timing (i.e., from button press to activation). To be able
to set in context, the signal timing information needed in order to analyze a network configuration of
signals and frames, a timing model is used. his section defines the required information that must
be provided by an application programmer in order to be able to guarantee the end-to-end timing
requirements.
A Volcano signal is transported over a network within a frame. Figure . identifies six time points
between the generation and consumption of a signal value.
The six time points are
. Notional generation (signal generated), either by hardware (e.g., switch pressed) or
software (e.g., timeout signaled). he user can define this point to best reflect their system.
. First v_output() (or v_imf_tx() for an immediate frame) at which a new value is available.
This is the first such call after the signal value is written by a write call.
. The frame containing the signal is first entered for transmission (arbitration on a CAN
bus).
. Transmission of the frame completes successfully (i.e., the subscriber's communication
controller receives the frame from the network).
. v_input() (or v_imf_rx() for an immediate frame) makes the signal available to the
application.
. Notional consumption, the user application consumes the data. he user can define this
point to best reflect their system.
