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Chapter 2 Function Reference — WFM_Check
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National Instruments Corporation 2-405 NI-DAQ FRM for PC Compatibles
pointsDone returns the number of points written to the analog output channels specified in
chan for the current buffer iteration. For devices that have analog output FIFOs, pointsDone
returns the number of points written to the FIFO if chan belongs to group 1. Refer to the
following Using This Function section for more information.
Range: 0 to count – 1, where count is the parameter used in the last
WFM_Load call.
Note C Programmers—wfmStopped, itersDone, and pointsDone are
pass-by-reference parameters.
Using This Function
WFM_Check returns status information concerning the progress of a waveform generation
operation. It is useful in determining when an operation has completed and when you can
initiate a new operation.
A FIFO lag effect is seen for group 1 channels on devices with analog output FIFOs.
pointsDone and itersDone indicate the number of buffer points currently written to the FIFO.
There is a time lag from the point when the data is written to the FIFO to when the data is
output to the DACs. This time lag is dependent upon the update rate. For example, if you had
a buffer of 50 points that you wanted to send to analog output channel 0, the first call to
WFM_Check would have itersDone = 20. The FIFO would be filled up with 20 cycles of your
50-point buffer. Refer to the FIFO Lag Effect on the MIO E Series, AT-AO-6/10,
AT-MIO-16X, AT-MIO-64F-5, PCI-4451 and PCI-4551 section of Chapter 3, Software
Overview, of the NI-DAQ User Manual for PC Compatibles for a more detailed discussion.
wfmStopped is also affected by the FIFO lag, since wfmStopped indicates when the last
point has actually been output.
On the PCI/PXI/CPCI E Series devices, you can effectively turn off the FIFO to eliminate the
FIFO by effect. Refer to the
AO_Change_Parameter
function.
Note AT-MIO-16X, E Series devices, AT-MIO-64F-5, AT-AO-6/10, and 4451 devices
only—If you use FIFO mode waveform generation, pointsDone is always 0. If the
generation is continuous (including pulsed waveform generation), the parameters
wfmStopped and itersDone are always 0; otherwise wfmStopped and itersDone
indicate the status of waveform generation operation.