United Electronic Industries PD2-MF, User Manual

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Appendix C: Application Notes
111
To receive notification on a sample or scan count boundary, the buffer
is segmented into frames. Whenever the data transferred to the buffer
crosses a frame boundary, the driver sends an event to the application.
This event "wakes up" the application thread that is responsible for
processing data in the buffer. To keep the frame boundaries at fixed
buffer locations, the buffer size should be a multiple of the frame size.
If multi-channel acquisition is performed, then the frame size should
also be a multiple of the scan size. Doing so keeps the pointer
arithmetic from becoming unnecessarily complex.
With the ACB, three modes of operation are possible:
•
Single Buffer
•
Circular Buffer
•
Recycled Circular Buffer
In all three modes, data is written to the beginning of the buffer at the
start of acquisition. The three modes differ in what is done when the
end of the buffer is reached and if the buffer head catches up with
the buffer tail.
Single Buffer
In the Single Buffer mode acquisition stops when the buffer end is
reached. In this mode the application can access the buffer and process
the data any time during acquisition or wait until the buffer is full and
acquisition stops. The Single Buffer mode is the simplest to program,
and also the most common, is useful in applications where acquiring
data in a continuous stream is not required. This is similar to the way
digital multi-meters and digital storage oscilloscopes acquire signals,
whereby a single buffer is filled, and then the waveform is displayed.
This process can also be repeated for any number of times.