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Peek FIFO (Clock-Driven Logic)

Last Modified: February 27, 2020

Returns the oldest element of a FIFO without removing the oldest element.

Peek FIFO is supported on all local, DMA host-to-target, and peer-to-peer reader FIFOs, regardless of the implementation type.

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Note

Peek FIFO must be in the same clock domain as the Read FIFO node. Otherwise, the program returns a code generation error when you try to compile the FPGA VI.

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reference in

Reference to the FIFO.

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error in

Error conditions that occur before this node runs.

The node responds to this input according to standard error behavior.

Standard Error Behavior

Many nodes provide an error in input and an error out output so that the node can respond to and communicate errors that occur while code is running. The value of error in specifies whether an error occurred before the node runs. Most nodes respond to values of error in in a standard, predictable way.

error in does not contain an error error in contains an error
If no error occurred before the node runs, the node begins execution normally.

If no error occurs while the node runs, it returns no error. If an error does occur while the node runs, it returns that error information as error out.

If an error occurred before the node runs, the node does not execute. Instead, it returns the error in value as error out.

Default: No error

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ready for output

Boolean value that specifies whether downstream nodes are ready for this node to return a new value.

Use Feedback Node to wire this input to the ready for input input of a downstream node. If this input is False during a given cycle, output valid returns False during that cycle.

True The downstream node is ready for the next data element.
False The downstream node is not ready for the next data element.

Default: False

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reference out

Reference to the FIFO.

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data

Oldest data element in the FIFO.

If the FIFO is empty, data returns an undefined element.

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error out

Error information.

The node produces this output according to standard error behavior.

Standard Error Behavior

Many nodes provide an error in input and an error out output so that the node can respond to and communicate errors that occur while code is running. The value of error in specifies whether an error occurred before the node runs. Most nodes respond to values of error in in a standard, predictable way.

error in does not contain an error error in contains an error
If no error occurred before the node runs, the node begins execution normally.

If no error occurs while the node runs, it returns no error. If an error does occur while the node runs, it returns that error information as error out.

If an error occurred before the node runs, the node does not execute. Instead, it returns the error in value as error out.
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output valid

Boolean value that indicates whether this node computes a result that downstream nodes can use.

Wire this output to the input valid input of a downstream node to transfer data from the node to the downstream node.

True Downstream nodes can use the result this node computes.
False This node returns an undefined value that downstream nodes cannot use.
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Note

This node may return different undefined values when executed in simulation mode versus when executed on hardware.

Handshake Protocol

Because this node may return invalid data in certain cases, such as when the FIFO is being cleared or the FIFO is currently empty, this node uses the four-wire handshake protocol to alert you if this node returns invalid data. Check the status of output valid to ensure the data output is valid.

Where This Node Can Run:

Desktop OS: none

FPGA: All devices

Web Server: Not supported in VIs that run in a web application


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