Intel Core Duo USB Issue: A Mischaracterized Bug

Final Words

First of all, it's important to characterize the impact of the USB 2.0 asynchronous scheduler bug on both Core Duo and Pentium M based systems.  Using the Lenovo T60 and T43 as comparison points, we found that without the fix, adding a bus-powered USB device such as a memory stick reduced battery life anywhere from 18 - 28%.  In the case of the T43, a 28% reduction in battery life for simply plugging in a USB 2.0 device is beyond ridiculous.  In the case of both notebooks, applying Microsoft's fix gives you almost all of your battery life back. The only decrease is due to actual power used by the device and any polling that may be happening as a result of the device being installed. 

It is also extremely important that we point out the existence of this bug on all of the platforms that we tested; in other words, this is not exclusively a Core Duo problem.  In fact, in the case of the T60/T43, the Sonoma based T43 actually lost a larger percentage of its battery life due to the asynchronous scheduler bug than the Napa based T60.  We saw the same results with the ASUS notebooks. With only the integrated USB 2.0 camera connected, the ASUS Napa notebook lost 17% of its battery life due to the bug, while the Sonoma based W5A lost 25.5%.  Once again, implying that this is a Core Duo issue alone is simply incorrect; the problem affects Sonoma platforms just as much, if not more, than Core Duo platforms.  Based on the results that we've seen in our perfmon analysis, we tend to believe Microsoft's assessment that the problem would exist on any system that spent any time in C3 or lower power states.

Thankfully, the Microsoft fix does seem to work pretty well. The only downside is that the problem re-appears after bringing your notebook out of stand-by.  Although a simple reboot will fix the problem once more, it's not a practical long term solution.  Unfortunately, we have absolutely no idea when a true fix will be put in place.  Until Microsoft releases a fix, we can only suggest that all notebook users, regardless of your CPU, either implement the temporary fix that we outlined in this article or be very conscious of leaving USB 2.0 devices connected while on battery power.