How to Use the FlexRadio Firewire Driver DPC Latency Checker to...

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How to Use the FlexRadio Firewire Driver DPC Latency Checker to...

How to Use the FlexRadio Firewire Driver DPC Latency Checker to Determine Operating Mode

  System Dependencies
  Minimum PowerSDR Version:     N/A 
  Applicable Hardware:     Any SDR using the FLEX Firewire driver 

Content provided by: FlexRadio Systems Engineering

Version and above of the FlexRadio Systems' FLEX Firewire driver has a very accurate DPC (deferred procedure call) analysis tool that will automatically estimate the proper WDM operating mode for the Firewire driver for both Windows XP and Vista (32 & 64-bit).

In order for the DPC Latency Checker to provide an accurate assessment of the recommended operation mode, you must check your system with all of the applications you would normally be using at the same time with your FlexRadio transceiverSo if you use a logging program, digital mode programs, e-mail clients, web browsers and PowerSDR specific third-party utilities such as the VoiceKeyer and DDUtil (just to mention a few) at the same time with PowerSDR these programs must be loaded and fully operational (not just sitting idle) along with PowerSDR running.

Also, you need to run the DPC Latency Checker for at least 5 minutes to get a sufficient sampling duration for the results to be accurate as possible.  A test duration period longer than 5 minutes is even better.

Even though the DPC checker may indicate that you can use the Normal operation mode, is still highly recommended that you use Safe Mode 1 as the Operation Mode.  DPCs are only one component that can adversely effect the performance of a real-time audio processing application such as PowerSDR.  Normal mode operation is only recommended if the PC and all of the programs running on it do not induce long duration DPC, such as when you use a dedicated PC environment to run PowerSDRIf you do receive audio drop outs and program freezes when operating with the normal mode, immediately revert to the recommended Safe Mode 1 setting.

To determine your preferred operating mode, double left click on the FLEX Firewire Control Panel icon to open the Control panel.
  1. In the Global Settings area, click on the DPC button at the top left of the screen
  2. Left click on the radio button labeled "Enable DPC Latency Checker"
  3. You will see the DPC latency values displayed in the box below the linear time scale and the Recommended WDM Operation Mode box will be populated with the suggested operating mode.  In the example below the Max Latency is 81 microseconds (us) and the recommended WDM Operation Mode is Normal Mode.

  4. The Operation mode will automatically be set to the recommended value.
  5. To reset the DPC test, click on the Reset button.  You may want to run several tests with different third-party applications running to determine which ones are more likely to result in long duration DPCs.  Microsoft Outlook is one program known to be very bad for initiating long duration DPCs.
You can always over-ride the suggested Operation mode and select a mode that is more forgiving of longer duration DPCs and can provide a more stable operating environment for the FlexRadio transceiverIf you experience audio "freeze ups" or slight glitching of the received audio, change the Operation mode to one of the Safe Mode values.

This KB article may reference additional files that are available on the FlexRadio Systems web site Downloads page. Please use the URL(s) below to download the referenced materials.

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Last Modified:Saturday, April 18, 2009
Last Modified By: Administrator
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