FIFO.Acquire Write Region (Invoke Method)

LabVIEW 2018 FPGA Module Help


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

Requests a region to write to the host memory buffer in the target device driver and returns an external data value reference to this region. This method automatically starts the DMA channel if called without a previous call to the Start method.

Note  This method is available only if you have specified in the General FIFO Properties page that the FIFO Type is Host to Target—DMA.

Refer to Improving Efficiency When Accessing DMA FIFOs for more information about using this method.

Use the Invoke Method function to implement this method.

FPGA VI Reference In is a reference to an FPGA VI. You must open a reference to the FPGA VI to use this parameter.
error in describes error conditions that occur before this node runs. This input provides standard error in functionality.
Number of Elements specifies the size in elements of the buffer region being acquired.
Note  NI recommends that Number of Elements be a clean integer divisor of the host FIFO size. You configure the host FIFO size using the FIFO.Configure method. For example, for a host FIFO size of 32,768 elements, and a Number of Elements of 8,192, four calls to the Acquire Write Region method fills the FIFO buffer. In this example, subsequent calls to the Acquire Write Region method start over at the beginning of the FIFO. However, if Number of Elements is not a clean integer divisor of the host FIFO size, LabVIEW writes to a partial region of data at the end of the FIFO. In this case, Elements in Region returns the actual number of elements in the region.
Timeout (ms) specifies the minimum number of milliseconds the Invoke Method function waits before timing out. The Invoke Method function times out if the region is available for access but the requested number of empty elements is not available, or if part of the region is not yet available for access. The default is 5000 milliseconds. Set this parameter to –1 if you want the Invoke Method function to wait indefinitely.
FPGA VI Reference Out returns a reference to an FPGA VI.
error out contains error information. This output provides standard error out functionality.
Write Region Reference is the reference to the array of elements allocated by the device driver. You must delete this external data value reference before the driver can read new data from the specified portion of the buffer.
Elements in Region returns the total number of elements in the acquired memory region.
Empty Elements Remaining returns the number of elements in the host memory buffer that are available for writing.

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