Real-Time FIFO Page (Shared Variable Properties Dialog Box)

Requires: Real-Time Module

Select Real-Time FIFO from the Category list of the Shared Variable Properties dialog box to display this page.

Use this page to enable and configure the real-time features of a shared variable.

This page includes the following components:

  • Enable RT FIFO—Enables the real-time FIFO for a shared variable of type single-process or network-published. If you configure a network-published shared variable with network buffering and you enable the Real-Time FIFO, the network buffer must be as large as one FIFO element to ensure that data can be written. If the network buffer is smaller than a FIFO element, the network buffer overflows and no data transmits over the network.

    If you enable the Real-Time FIFO on a shared variable of waveform data type, the variant element of the waveform does not transfer because variants are variable-sized and therefore incompatible with the Real-Time FIFO.
    • FIFO Type—Specifies the type of FIFO configuration to use. If the shared variable contains an array data type, you must specify the number of array elements. If the shared variable contains waveform data type, you must specify the number of points per waveform. If you select an array of waveform data type, you must specify both the number of waveform elements per array and the number of points per waveform. You must specify the required number of elements and/or waveform points exactly to avoid memory allocations that can cause jitter.
      • Single Element—Specifies a FIFO buffer with a single element.
      • Multi-element—Specifies a FIFO buffer with multiple elements. If you choose this option, you also must specify the number of FIFO elements to use.
      • Use network buffer configuration—Uses the configuration you specify in the Use Buffering section of the Network page to configure the size and elements of the FIFO. This option is available only if you enable network buffering.

To prevent data loss due to buffer overflow, consider using both the network buffer and the Real-Time FIFO buffer. Refer to the National Instruments Web site for additional information about how buffer configuration affects shared variable performance.

Note  RT FIFOs do not support data types of variable size, such as clusters, strings, and variants. If you use a Real-Time FIFO to transfer waveform data, the variant element of the waveform does not transfer because variants are variable-sized and therefore incompatible with the Real-Time FIFO.

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