Low Level Streaming VIs

Low Level Streaming VIs

Data_Stream_Control_(Additive).vi

Use this VI in additive stream functions. This VI splits the stream control between fast data interface loops and slow data control/processing loops.

Monitor Stream.vi

This polymorphic VI provides several monitoring functions for FPGA streams. Refer to the specific instance VIs for details.

This VI contains the following instance VIs:

• Monitor FIFO Health.vi
• Monitor Minimum Samples Ready.vi

Monitor FIFO Health.vi

Use this VI to enable applications to keep track of various parameters of a FIFO under control. This VI is optional, and is often most useful in diagnosing problems with throughput.

You can also use this VI to allow the host to wait for the FIFO to be full enough or empty enough to begin a transfer. This process is called priming the FIFO, and it ensures that data is available to use before starting a stream. If you want the FPGA to manage waiting for the FIFO to be primed, use the Monitor Minimum Samples Ready VI.

Connect all terminals with a number suffix to the host by controls and indicators. The number allows the host to resolve different stream numbers from the host interface.

Note Some terminals are optional.

This VI is commonly used in conjunction with the Wait for Samples Ready or Get Stream Samples Ready host VIs, which inspect the value in stream.num samples ready N.

Parameters

samples in fifo Connect the output of the FPGA FIFO Method Get Number of Elements to Read or Get Number of Elements to Write for the FIFO that will be monitored.

stream.reset health monitor N Connect a control to this VI to allow the host to clear the state of the monitor and to clear the memory of the outputs stream.max samples ready and stream.min samples ready.

stream.num samples ready N reflects the current value reported to the samples in fifo terminal.

stream.max samples ready N reflects the highest value reported to the samples in fifo terminal since the last reset.

stream.min samples ready N reflects the lowest value reported to the samples in fifo terminal since the last reset.

Monitor Minimum Samples Ready.vi

This VI enables the FPGA to independently manage waiting for the FIFO to be primed. This VI is optional, and is most often useful in applications that require uninterrupted streaming output.

If you want the host to manage waiting for the FIFO to be primed, use the Monitor FIFO Health VI.

Connect all terminals with a number suffix to the host by controls and indicators. The number allows the host to resolve different stream numbers from the host interface. However, this VI does not have a standard VI on the host to program this value. Use the stock NI-RIO FPGA Host Interface to write to the controls.

Parameters

stream.minimum elements to start N specifies the minimum number of samples to wait for permission to use before asserting the output ready for start to True.

stream.num samples N should be connected to the stream.num samples N control used in the Data Stream Control VI. This connection enables you to specify a transfer size smaller than the minimum but still automatically start when all data to be transferred is ready.

permissed elements Connect the output of the FPGA FIFO Method Get Number of Elements to Read or Get Number of Elements to Write for the FIFO that will be monitored.

ready for start is enabled when the minimum number of samples that you specified in stream.minimum elements to start N is reached.