As FLEX-5000 beta testers, we used this tool to identify potential problems with the Firewire device driver and in the process got to understand how DPC latencies adversely effected performance.
In addition to hardware device drivers, applications too can generate long DPCs. MS Outlook and Media Player are VERY BAD about doing this adding sometimes up to 300 ms (1/3 of a second) of latency, which, for an almost real-time application such as PowerSDR, is an eternity. If you have DPC latencies in the 250 to 300 ms range when not running PowerSDR, you will need to try to find the culprit, if there is one to be identified. Sometimes it can be solved easily by upgrading a hardware driver. Other time it takes actually upgrading the hardware (video cards, for one). I have a fairly fast laptop, but the average DPC latency is 260 ms with spikes up to 350 ms and it is essentially useless for running PowerSDR above a 48K sampling rate. I have updated all of the drivers and tried to find a "silver bullet" application or service that is running that causes the long DPC latencies, but I can not find it. Conversely, my Core2 Duo has an average DPC latency of 35 uS (microseconds) and it is a screamer running PowerSDR...as long as I do not run Outlook and/or Media Player, which when very small buffers are used running at a 192 KHz sampling rate, will result in audio drop outs This is just one tool that will give you some insight into how well you system is performing or is prepared to perform. -Tim -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Peter G. Viscarola Sent: Monday, August 06, 2007 3:21 PM To: FlexRadio@flex-radio.biz Subject: Re: [Flexradio] Fw: Helpful software > >Flexers might find the DPC Latency checker of use. You can download it >free at the Thesycon site under "Free Utilities" > EXCELLENT suggestion, Mike, thanks! I know Udo Eberhardt (who runs the company that wrote this tool), and I wasn't even aware of this utility. So, thanks very much! Interpreting the results can be tricky, even if you're a Windows driver developer. Keep in mind the tool reports ISR to DPC latency... not device interrupt request to ISR latency. ISR to DPC latency is best thought of as the time it takes from a device's interrupt being serviced to when that device is able to start returning data to an application. This is typically the type of latency that really matters to device in a Windows system. Note that the AVERAGE ISR to DPC latency is almost never a problem. Rather, what you're looking for is the repeated occurrence of "outliers"... worst-case ISR to DPC latency. The bad part of all this is if you experience packet loss as a result of excessive worst-case (or even average) ISR to DPC latency, there's often little you can do about it. You're mostly restricted to changing the devices involved... and it's rarely the device you're concerned about that's the problem. I knew of an infamous network card that created well over 1ms of ISR to DPC latency (for other drivers in the system) each time it periodically checked the speed of the network to which it was connected. Devices that were "backed up" behind this NIC often suffered from overruns and dropped data. Swap the NIC, and problems with those other devices disappeared. The worst offenders, in terms of causing excessive ISR to DPC latency for other system devices, are typically video and network cards. Thanks again, Mike, for making us all aware of this tool, de Peter K1PGV _______________________________________________ FlexRadio mailing list FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archive Link: http://www.mail-archive.com/flexradio%40flex-radio.biz/ FlexRadio Knowledge Base: http://kb.flex-radio.com/ FlexRadio Homepage: http://www.flex-radio.com/ _______________________________________________ FlexRadio mailing list FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archive Link: http://www.mail-archive.com/flexradio%40flex-radio.biz/ FlexRadio Knowledge Base: http://kb.flex-radio.com/ FlexRadio Homepage: http://www.flex-radio.com/
