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General Page (Memory Properties Dialog Box)

LabVIEW 2013 FPGA Module Help

Edition Date: June 2013

Part Number: 371599J-01

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Requires: FPGA Module

In the Memory Properties dialog box, select General from the Category list to display this page.

Use this page to edit properties for memory items.

This page includes the following components:

  • Name—Specifies the name of the memory item that appears in the Project Explorer window or in the VI-Defined Memory Configuration node. The name also appears in the Memory Method Node on the block diagram.
  • Requested number of elements—Specifies the number of elements you want to hold in the memory item. The actual memory usage, in bytes, depends on the number of elements and data type you specify.
  • Implementation—Specifies how the FPGA stores this memory item. Contains the following options:
    • Block Memory—Stores the data using embedded blocks of memory. Xilinx literature describes this implementation as block RAM or BRAM. Memory items using embedded block memory take one clock cycle to execute. Use block memory in the following situations:

      • In a single-cycle Timed Loop, when you do not need to access this memory during the same cycle as the one in which you give the address.

      • When the amount of memory you need is large.

      • When you do not have enough free logic resources available on the FPGA.

      This option contains the following component:
      • Actual number of elements—Returns the configured number of elements. Sometimes the requested number of elements is not compatible with the memory configuration. In these case, the Actual Number of Elements is coerced to a compatible number.
    • Look-Up Table—Stores the memory item in look-up tables available on the FPGA. This storage consumes logic resources that the FPGA uses for other logical operations, such as addition and subtraction. Xilinx literature describes this implementation as distributed RAM or LUT RAM. Use look-up tables in the following situations:

      • You are accessing this memory in a single-cycle Timed Loop and need to read data from the memory item during the same cycle as the one in which you give the address.

      • The amount of memory you need is smaller than the minimum amount of embedded block memory on the FPGA.

      • You do not have enough free embedded block memory on the FPGA.

      This option contains the following component:
      • Actual number of elements—Returns the configured number of elements. Sometimes the requested number of elements is not compatible with the memory configuration. In these case, the Actual Number of Elements is coerced to a compatible number.
    • DRAM—Stores the memory item in DRAM available on the FPGA. Not all hardware supports using DRAM for memory. See the DRAM Properties page of the FPGA Target Properties dialog box to configure how LabVIEW implements the DRAM in the project. This option contains the following components:
      • Actual number of elements—Returns the configured number of elements. Sometimes the requested number of elements is not compatible with the memory configuration. In these case, the Actual Number of Elements is coerced to a compatible number.
      • Maximum outstanding requests for data—Specifies the number of maximum requests for data the application allows to be outstanding.
      • DRAM bank—Specifies which DRAM bank to use.
        • Allocated here—Indicates the amount of memory allocated in this memory item.
        • Allocated elsewhere—Indicates how much memory is allocated in other items.
        • Available—Indicates how much memory is still available in the bank.
        • Total physical size—Indicates the total size of the bank.
  • Persist memory values between VI executions while executing on the development computer—If you leave this checkbox disabled, the values in this memory item will reset to the initial values as specified on the Initial Values page of the Memory Properties dialog box between VI executions while executing on the development computer. If you place a checkmark in this checkbox, LabVIEW retains values in this memory item between VI executions while executing on the development computer, but may result in higher memory consumption and slower execution for large memories. By default, this checkbox does not contain a checkmark for new LabVIEW projects.
    Note  The checkbox contains a checkmark for previous versions of LabVIEW projects in order to maintain the behavior of previous versions of FPGA applications.

 

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