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Why Can't I Run My R Series Analog Output Channels at the Maximum Update Rate on NI-RIO 2.4.0 or later?

Primary Software: LabVIEW Modules>>FPGA Module
Primary Software Version: 8.5
Primary Software Fixed Version: N/A
Secondary Software: Driver Software>>NI-RIO
Hardware: Reconfigurable I/O (RIO)>>R Series

Problem:
Since NI-RIO 2.4.0, the analog output channels on my R Series card will not achieve the maximum update rate. Why is this?

Solution:
In order to achieve the maximum update rate with your R Series card using NI-RIO 2.4.0 or later, make sure to follow the steps listed below.

1. Right-click on the analog output channel in the project and change the arbitration to Never or Multiple Requesters Only.  NOTE: This will only work if you have exactly one IO node in your application writing to that channel.
2. Simplify your loop and make sure that all tasks are done in parallel. Reading a control takes a few ticks. If you read a control and then wire it directly to the analog output channel, it increases your loop time since both actions happen serially. A better option would be to perform tasks in parallel. For information on using parallel execution in LabVIEW FPGA, see the NI Developer Zone tutorial on Optimizing your LabVIEW FPGA VIs: Parallel Execution and Pipelining. 
   

Related Links: NI Developer Zone Tutorial:  Optimizing your LabVIEW FPGA VIs:  Parallel Execution and Pipelining
LabVIEW 8.5 FPGA Module Help:  Pipelining to Optimize FPGA VIs
LabVIEW 8.5 FPGA Module Help:  Understanding Arbitration Options

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Report Date: 06/16/2008
Last Updated: 06/19/2008
Document ID: 4MFDED3S

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