1. 2. 3. How to Use the FlexRadio Firewire Driver DPC Latency ...

How to Use the FlexRadio Firewire Driver DPC Latency Checker to Determine Operating
Mode
How to Use the FlexRadio Firewire Driver DPC Latency Checker to Determine Operating
Mode
System Dependencies
Minimum PowerSDR Version:
Applicable Hardware:
N/A
Any SDR using the
FLEX Firewire driver
Content provided by: FlexRadio Systems Engineering
Version 3.4.0.5254 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 transceiver. So 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 PowerSDR. If 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.
5.
The Operation mode will automatically be set to the recommended value.
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
transceiver. If 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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KB Source Document(s):
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Last Modified By: Administrator, Saturday, April 18, 2009
http://kc.flex-radio.com/KnowledgebaseArticle50328.aspx
Sunday, July 12, 2009