User manual

Chapter 4 NI-DAQ Double Buffering

Figure 4-1 illustrates a series of sequential data transfers.

Figure 4-1. Double-Buffered Input with Sequential Data Transfers

The double-buffered input operation begins when the DAQ device starts

writing data into the first half of the circular buffer (Figure 4-1a). After the

device begins writing to the second half of the circular buffer, NI-DAQ can

copy the data from the first half into the transfer buffer (Figure 4-1b). You

can then store the data in the transfer block to disk or process it according

to your application needs. After the input device has filled the second half

of the circular buffer, the device returns to the first half of the buffer and

overwrites the old data. NI-DAQ can now copy the second half of the

circular buffer to the transfer buffer (Figure 4-1c). The data in the transfer

buffer is again available for use by your application. The process can

be repeated endlessly to produce a continuous stream of data to your

application. Notice that Figure 4-1d is equivalent to the step in Figure 4-1b

and is the start of a two-step cycle.

Incoming

Device Data

Circular Buffer

Transfer Buffer

Empty Buffer

Untransferred Data Transferred Data

a. b.

c. d.