How to do another thing before returning of a buffered waveform generation?
Hi There,
The DAC0 and DAC1 of PCI-6024E are used to generate waveforms by the buffered analog output mode. We know that before the buffered generation is completed, the starting function of generating waveform, either "WFM_op" or "WFM_Group_Control",will not return, unless you call "Timeout_Config". In my application developed by Visual C++, I hope that after starting the waveform generation process, I can do another thing, for example, plotting data or data processing. Would you tell me how to do that? I greatly appreciate you for any reply and suggestions.
Kylin
Kylin,
Actually, WFM_Group_Control() is not synchronous. It is asynchronous and will return immediately after the generation has been started. I would suggest that you take a look at the following examples. They are located in C:\Program Files\National Instruments\NI-DAQ\Examples\VisualC\Ao:
WFMsingleBufAsync.C
WFMsingleBufSync.C
WFMsingleBufAsync.C is an asynchronous generation that uses WFM_Group_Control(). On the other hand, WFMsingleBufSync.C is a synchronous generation that uses WFM_Op(). In your situation, you would want to follow the programming structure of WFMsingleBufAsync.C.
Good luck with your application.
Spencer S.
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"Why does the double buffered waveform generation pause after the first buffer before continuing?"
"I am using an AT-AO-10 board to generate a multiple channel waveform in double buffered mode. The board's DAC's are updated by an external clock signal. While the waveform generation performs well, I notice that after the first buffer has been generated there is a time delay before the next buffer is output. However the second buffer and thereafter perform well without any time delays. If anyone can provide me an explanation on why this happens I would appreciate it. I am using NI-DAQ API functions to generate the waveforms and my settings for the WFM_DB_Config function are 1 for oldDataStop to disallow regeneration of data and 0 for partialTransferStop to not stop when a half buffer is partially transferred."
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"Vadi,
The first thing is to make sure that you have the latest version of NI-DAQ installed, NI-DAQ 6.9.1. If you need to install it, make sure you completely uninstall any prior versions. Then, you will have examples installed in either the NI-DAQ or the CVI directory. In the AO directory, you should find the WFMdoubleBuf example.
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I have checked my version of NI-DAQ and it is 6.9.1. I am generating the double buffered waveform according to the format shown in WFMdoubleBuf and with some modifications from WFMsingleBufExtUpdate to allow me to use my external update clock. However I continue to notice the same phenomena again and again. For a buffer size of 7500 or 10000 points there is a time lag meaning after the first buffer has been output there is a noticeable time delay before the second buffer and buffers there after is output. This time lag doesn't exist for the buffers that are output after the first buffer but it does exist for the first buffer. When I decrease the buffer size down to 5000 points the time lag disappears (Note: this phenomena also occurs when I use an internal time base as opposed to my external clock). Is there a reason for this? I am using a AT-AO-10 board and I know the on board FIFO is 1024 points deep. However from the documentation provided it doesn't indicate that double buffered mode uses the on board FIFO at all. In fact, the functions require that the FIFO mode be turned off (in WFM_Load) for double buffered waveform generation. Is there a reason why when the buffer size is increased that there is a time lag after the first buffer? Is this because of the functions themselves or is this because of the AT-AO-10 board?Vadi,
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