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Old September 22, 2013, 04:53 AM
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Join Date: Feb 2008
Location: Czech republic
Posts: 394

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Question Latency compare USB to PS/2 ports?

Mouse and keyboard lag is quite a issue for fast first person shooter games. They tend to get so fast, that my poor PC cannot compete with most, yet still I wonder, if there are tools how to measure the input lag of devices like mouse and keyboard.

For a old-school machine, I use PS/2 ports for both, yet the MX510 Logitech mouse is by original a USB device, connected only by the adapter to PS/2. That make one wonder, if the adapter could not contribute some lag on it's own... (and I think the answer is a definitive yes, it have to)

So that is why I trying to push the PS/2 ports speed up:

...but w/o being able to measure how things get faster, I have no idea if this is helping or not. Default rate is 60, witch seems to be to be awfully low...

There is a great article about it at Anadtech: AnandTech | Exploring Input Lag Inside and Out
...with many hi-fremerate videos to catch the speeds precisely, however any software tools or anything that could be used to determine the lag was not used at all.

There do exist a latency analyze tools for system devices, like this one:

DPC Latency Checker

(showing example of what bad videoplayback is on JetWay V266B mobo (KT266A), because the stupid mainboard pull everything on IRQ7 - that it, on IRQ7 is - GFX card, Sound, NIC card and USB...! Even that FIVE other IRQ's are completely free: IRQ 3, 4, 5, 10 and 11 to be precise.

So, do exist something for the keyboard/mouse that could determine how difference is there between the USB and PS/2 mouse connection? Anyone have any slightest idea about this?
"It is dangerous to be right in matters on which the established authorities are wrong." - Voltaire
"I believe that all the people who stand to profit by a war and who help provoke it should be shot on the first day it starts..." - Hemingway :) my config - my caps
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Old September 22, 2013, 10:35 AM
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Join Date: Feb 2010
Location: Markham
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For mice USB is almost always faster than PS/2, due to the way USB mice emulate PS/2 and also have the option to overclock to 1000hz.

In your case, the MX510 performs best over USB at 1000hz. The mouse is old enough that there's plenty of documented testing on its performance. Here's an example: ESR - ESReality MouseScore 2007 The mouse tested is an MX500, but the MX510 is completely identical with the exception of an additional angle snapping algorithm on a hardware level. (A2020 sensor vs S2020)

Although overclocking the USB port is always a good thing on the MX510 it doesn't hold true for all mice. Best to use software like Enotus mouse test alongside Outerspace's max IPS logger to make sure you're actually gaining tracking performance. Tracking is always more important than mouse rate once you get over 250hz.

The software mentioned above can track your USB polling rate, but if you really wanted to test for yourself the difference between PS/2 and USB you can use Mouse Rate Checker or Direct Input Mouse Rate.

As for keyboards, PS/2 is generally faster than USB due to the way IRQ's work. However, if you can get your USB keyboard to a fairly high polling rate the difference is minimal. (>~500hz)
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