User`s guide

Continuous Data Transfer in PCIS-DASK • 65
6.2 Double-Buffered AI/DI Operation
PCIS-DASK uses double-buffering techniques in its driver software for
continuous input of large amounts of data.
6.2.1 Double Buffer Mode Principle
The data buffer for double-buffered continuous input operation is a circular
buffer logically. It is logically divided into two equal halves. The double-buffered
input begins when device starts writing data into the first half of the circular
buffer (Figure 6-1a). After device begins writing to the second half of the
circular buffer, you can copy the data from the first half into the transfer buffer
(user buffer) (Figure 6-1b). You now can process the data in the transfer buffer
according to application needs. After the board has filled the second half of the
circular buffer, the board returns to the first half buffer and overwrites the old
data. You now can copy the second half of the circular buffer to the transfer
buffer (Figure 6-1c). The data in the transfer buffer is again available for
process. The process can be repeated endlessly to provide a continuous
stream of data to your application (Figure 6-1d).
Incoming DMA
input data
Circular Buffer
Transfer Buffer
a
b
c
d
> > >
> > >> >
Empty Buffer Untransferred Data Transferred Data
> >
Figure 7-1