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D
Hardware and Software Interdependencies
The system hardware and software must work hand in hand to perform the tasks of image capture and decode. This is
accomplished by the cooperation between hardware, the hardware interface layer (provided by the designers of the host
system), the Image Acquisition layer, and the Operating System (OS) (if it exists).
The IMAGETEAM Layer requires two types of events used to track the progress of an incoming image. The first event, called
the Vsync Event, is typically defined as a hardware interrupt generated on the trailing edge of the vertical data window (see
below).
The Vsync event is used to indicate the end of the full frame of data. The IMAGETEAM layer also uses this event as a cue to
decide on the next exposure and write this new value to the imager, if necessary.
The second event type is sometimes referred to as the "line event." It is used by the IMAGETEAM layer as an indication that it
has partial image data that can (should) be preprocessed for tracking the effectiveness of the last exposure. This event needs
to occur several times during a frame capture. The frequency of the event may be tailored to the system timing to ensure
maximum efficiency. A balance needs to be reached relative to the time to launch and terminate the routine, and the length of
time the rest of the system can hold off while the IMAGETEAM layer performs its preprocessing tasks. A good rule of thumb for
this event is for it to occur no less than 6 times per frame, or every 80 lines. The method of generating this event can vary
depending on the system and on the designer's preference. The event can be indicated as a hardware interrupt based on
counting rows and generating an interrupt on a valid compare to the desired row count interval. The event may also be triggered
based on an elapsed time interval. The interval may be tracked using a hardware timer or an OS scheduler. The event
occurrence is then passed to the IMAGETEAM layer by an ISR or scheduler call.
IMAGETEAM™ 4X00 Series Integration Manual
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Vsync Event Signal
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D - 1
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