Real-Time Measurement and Control

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how to achieve deterministic data transfer between windows and RT



I use LabVIEW 8.6 and cRIO 9104. i read analog data values from NI 9215 module. In the FPGA, i have used DMA FIFO to transfer to RT. In the RT, i have used TCP/IP WRite to send data to Windows VI. When i see the wave form on

windows, the sine wave is slightly skewed at many points.

Also when  i switch OFF the input supply for 1000 milli sec and switch it ON again, the waveform on windows should fall immedaitely fall to low and again raise after switching ON.  But the windows waveform shows a delay . and it is not consistent.. The switching OFF and ON of the switch (digital channel) is done in RT thru FPGA Read/ Write control property.

Please let me know if it is a problem with data streaming to windows from RT.


Thank you.

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Message 1 of 3

It is possible to perform the transfers as you describe.  We do it all the time.  You need to look at all the statuses of the various methds you are using to make sure that you are not losing data by overflows.  By setting the queue/fifo sizes and insuring that you are servicing the queues/fifos appropriately, you will achieve gap free communication.  Even after you have achieved this, there will be latency between when your windows graphs show the data.  If your command starts in windows, you will not see the result in windows for a considerable period of time.  Add a counter to the source of your data and look at the counter in windows to see if you are missing data.  Note the counter value when you issue a command and compare to the counter value on your expected response to determine your round trip time.

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Message 2 of 3

Hi Joshna,


Both of the examples below implement lossless TCP streaming from RT to Windows. However, network communication is not deterministic, so you may see some delays as you mention. How large are the delays?



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Message 3 of 3