PC2-Comp Express
Theory of Operation
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25
A/D
Onboard
Memory
Trigger
Camera
Start of
image
End of image
capture
End of PCIe
transfer
PCIe
Controller
Host
Memory
Figure 7: Acquisition/Transfer Interrupts
Event-Related Definitions
Interrupt
An interrupt is a signal sent by the PC2-Comp Express board to the computer CPU
that indicates an event on the frame grabber. The PC2-Comp Express device driver
has excellent event reaction time since interrupts are processed inside an interrupt
service routine (ISR) at kernel level.
Event
An event is a WIN32 object that can take two states: signaled and non-signaled. It is
used for thread synchronization. In this context, an event is associated with an
interrupt so that a WIN32 thread can be unblocked when the event it is waiting for
gets signaled. For example, when an interrupt is received, the corresponding event
is signaled and the thread waiting for this event resumes execution.
Acquisition Events
External Trigger (Used or Ignored)
The External Trigger event is generated when the external trigger pin is asserted, usually indicating the
start of the acquisition process. There are two types of external trigger events: ‘Used’ or ‘Ignored’.
Following an external trigger, if the event generates a captured image, an External Trigger Used event
will be generated (CORACQ_VAL_EVENT_TYPE_EXTERNAL_TRIGGER).
If there is no image captured, an External Trigger Ignored event will be generated
(CORACQ_VAL_EVENT_TYPE_EXTERNAL_TRIGGER_IGNORED). An external trigger event
will be ignored if the rate at which the events are received are higher than the possible frame rates of
the camera.
For more information, see "External Trigger" on page 29.
Vertical Sync from Camera
The Vertical Sync event indicates a vertical sync has been detected. Note that this does not necessarily
mean the image will be captured. For instance, if you have a free-running camera at 30fps with
external trigger enabled, you will get thirty events per second even though the PC2-Comp Express
waits for an external trigger to actually capture the next image. This allows the application program to
independently count frames coming from the camera. The Sapera event value is
CORACQ_VAL_EVENT_TYPE_VERTICAL_SYNC.
Summary of Contents for PC2-Comp Express OC-P2EM-COMP0
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