Request Data (Memory Method)

LabVIEW 2018 FPGA Module Help

Edition Date: March 2018
Part Number: 371599P-01
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Requires: FPGA Module

Queues requests for data from the DRAM memory on the FPGA target. Use this method in conjunction with the Retrieve Data method to read data from DRAM. To overcome the latency of DRAM, queue requests for data in bursts.

Use the Memory Method Node to implement this method. Only DRAM memory supports this method.


Block Diagram Inputs
Block Diagram Outputs

Block Diagram Inputs

Memory InSpecifies the FPGA memory. If you leave Memory In unwired, you can specify the FPGA memory by right-clicking the Memory Method Node and selecting a memory item from the shortcut menu. Otherwise, you can wire a Memory control, Memory constant, or another Memory Method node to Memory In.
AddressSpecifies the location of the data in memory on the FPGA target. The valid address range depends on the Requested number of elements you specify in the Memory Properties dialog box. For example, if you specify a Requested number of elements of 65536, the valid address range is 0–65535. If Address exceeds the address range, the Request Data method might access different memory than expected, causing output data from the Retrieve Method to be invalid.
Input ValidSpecifies whether the next data point has arrived for processing. Wire the output valid output of an upstream node to this input to transfer data from the upstream node to this node.

To display this handshaking terminal, configure the memory as DRAM.

Block Diagram Outputs

Memory OutReturns Memory In if Memory In is wired. Otherwise, Memory Out returns the memory that you specify in the Memory Method Node.
Ready for InputReturns TRUE if this node is ready to accept new input data. Use a Feedback Node to wire this output to the ready for output input of an upstream node.
Note  If this terminal returns FALSE during a given cycle, LabVIEW discards any data that other nodes send to this node during the following cycle. LabVIEW discards this data even if the Input Valid terminal is TRUE during the following cycle.
To display this terminal, configure the memory as DRAM.

Request Data (Memory Method) Details

This method specifies the order in which the Retrieve Data method returns data. You specify the maximum outstanding requests on the General page of the Memory Properties dialog box. To guarantee that you do not receive stale data, you should initialize the DRAM before using it.

Note  The Write (Memory Method) node can be placed in a different clock domain than the corresponding Request Data and Retrieve Data nodes.

Considerations for Single-Cycle Timed Loops

You only can use this method inside a single-cycle Timed Loop.


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