User manual

NI-DAQ Double Buffering

This chapter describes using double-buffered data acquisitions with

NI-DAQ. This chapter applies to counter operations. However, you can

read samples of any size.

Overview

Conventional data acquisition software techniques, such as single-buffered

data acquisition, work well for most applications. However, more

sophisticated applications involving larger amounts of data at higher

rates require more advanced techniques for managing the data. One such

technique is double buffering. National Instruments uses double-buffering

techniques in its driver software for continuous, uninterrupted input or

output of large amounts of data.

This chapter discusses the fundamentals of double buffering, including

specific information on how the NI-DAQ double-buffered functions work.

Note

Input and output refer to both digital and analog operations in this chapter.

Single-Buffered Versus Double-Buffered Data

The most common method of data buffering found in conventional driver

software is single buffering. In single-buffered input operations, a fixed

number of samples are acquired at a specified rate and transferred into

computer memory. After the memory buffer stores the data, the computer

can analyze, display, or store the data to the hard disk for later processing.

Single-buffered output operations output a fixed number of samples from

computer memory at a specified rate. After outputting data, the buffer

can be updated with new or freed data.

Single-buffered operations are relatively simple to implement, can usually

take advantage of the full hardware speed of the DAQ device, and are very

useful for many applications. The major disadvantage of single-buffered

operations is that the amount of data that can be input or output is limited

to the amount of free memory available in the computer.