User manual

Chapter 4 NI-DAQ Double Buffering
NI-DAQ User Manual for PC Compatibles 4-8 ni.com
Figure 4-5. Double-Buffered Output with an Overwrite Before Copy
For this situation, NI-DAQ returns an overwrite before a copy warning
(overWriteError). This warning indicates that the device has output
old data but the data was uncorrupted during output. Subsequent transfers
will not return the warning as long as they keep pace with the output device
as in Figure 4-4.
The second potential problem is when an output device retrieves data that
NI-DAQ is simultaneously overwriting with data from the transfer buffer.
NI-DAQ returns an overwrite error (overWriteError) when this occurs.
The situation is presented in Figure 4-6.
Outgoing
Device Data
Circular Buffer
Transfer Buffer
Empty Buffer
Untransferred Data Transferred Data
a.
c. d.
b.
Overwrite Before
Copy