Appendix D Common Questions
National Instruments Corporation
D-5
DAQCard E Series User Manual
7.
How does NI-DAQ treat bogus missed data transfer errors that can arise during
DMA-driven GPCTR buffered-input operations?
When doing buffered transfers using GPCTR function calls with DMA,
you can call
GPCTR_Watch
to indicate
dataTransfer
errors. NI-DAQ
takes a snapshot of transfers and counts how many points have been
transferred. If all the points have been transferred and the first instance
of this error occurs, NI-DAQ returns a
gpctrDataTransferWarning
indicating that the error could be bogus. If all the points have not been
transferred, NI-DAQ returns the genuine error. The error continues to
be returned until the acquisition completes. The above error occurs
because NI-DAQ disarms the counter from generating any more
requests in the interrupt service routine. Due to interrupt latencies, it is
possible that the counter may have generated some spurious requests
which the DMA controller may not satisfy because it has already
transferred the required number of points.
8.
What are the PFIs and how do I configure these lines?
PFIs are Programmable Function Inputs. These lines serve as
connections to virtually all internal timing signals.
If you are using NI-DAQ language interface, LabWindows, or
LabWindows/CVI, use the
Select_Signal
function to route internal
signals to the I/O connector, route external signals to internal timing
sources, or tie internal timing signals together.
If you are using NI-DAQ with LabVIEW and you want to connect
external signal sources to the PFI lines, you can use AI Clock Config,
AI Trigger Config, AO Clock Config, AO Trigger and Gate Config,
CTR Mode Config, and CTR Pulse Config advanced level VIs to
indicate which function the connected signal will serve. Use the Route
Signal VI to enable the PFI lines to output internal signals.
Warning:
If you enable a PFI line for output, do not connect any external signal
source to it; if you do, you can damage the DAQCard, the computer, and
the connected equipment.
