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Ask Dave
by Dave Hamilton

He from whom all Mac knowledge flows...

Freezing USB Mice Explained!
March 17th, 2000

Well, it seems as though this freezing USB mouse problem has gotten more attention than the tartar sauce at a fish-fry! There are many people having this problem, and so many different "workarounds" that folks have found to "solve" it. Today we'll dissect another (perhaps the last?) e-mail on this subject, and hope to put this issue to rest once and for all. If you have any questions, feel free to e-mail me or post in the Ask Dave Forums! Enjoy!

Susan Weatherholt writes, "I bought a Rev. B iMac in December, 1998, and my mouse has always frozen rather frequently, no matter what I do. Just based on observations, I have determined that it is most likely to freeze when the iMac has been on for a few hours. I had attributed that to heat, but RAM could also be the culprit. Usually I can "unfreeze" it by unplugging and replugging the USB mouse cord, but sometimes that doesn't work and I have to restart the whole computer by using "Force Quit." At other times the keyboard freezes at the same time the mouse does, so I am forced to disconnect the power to the iMac before restarting it (this CAN'T be a good thing). Lately I have been shutting down the iMac rather than letting it sleep when I'm not using it. Doing this cuts down on the frozen mouse problem. I had not thought much about it until my cousin bought an iMac this past January. I was IM'ing her, and she mentioned that her mouse kept freezing (are we beginning to see a pattern here?). I told her about plugging/unplugging USB, it worked, and we moved on. I had 32MB of RAM that came with my iMac and had Comp USA install another 32MB before I took the computer home. Do you think that second memory chip is defective? It had never occurred to me! How would I find out without paying them to take the RAM out to test it? (This could be more expensive than buying new RAM...really.)"

Susan, you're definitely right about one thing in your letter -- we ARE beginning to see a pattern here. I received more mail about this freezing mouse problem than I have on ANY other topic I've ever discussed (well, there was that BeOS thing -- See "Hello, Kettle? Pot calling… we're both black." -- but that's a different story). Anyway, there are TONS of iMac owners out there writing in with this problem. Some have found solutions, some haven't. I have never experienced this problem with any iMac that I've come into contact with and, despite my claims to the contrary, I really don't think I have magic hands. There's got to be SOMETHING going on here, but it isn't obvious what that might be... yet. Last time I mentioned that someone had this problem after installing bad RAM, but I just don't think that's the case with ALL the instances of this problem since it seems fairly widespread. Most people are able to "solve" this by unplugging and replugging the mouse, so that would point to software and drivers. USB devices are truly "hot pluggable", meaning they can be connected and disconnected while the computer is on. The way this works is essentially as follows: There's a piece of software that constantly monitors the USB port(s) -- for the sake of discussion we'll call that software the "USB Manager". When the "USB Manager" detects that a device has been plugged in (either at startup or later), it gets the hardware ID from that device, and attempts to load a driver for it from the Extensions folder (if the driver doesn't exist in the Extensions folder, Mac OS 9 will actually try to download it, but that's another story). Assuming the driver DOES exist, the "USB Manager" loads that driver and activates the device, making it available to the system. The opposite, of course, happens when the device is unplugged. The "USB Manager" notices this and UNLOADS the driver from "active" memory. This is, in my estimation, what seems to be happening with people who have written in with this problem. The system, for one reason or another, thinks the device has been unplugged and so it unloads the required drivers. Plugging the device back in seems to reload them (most of the time), and all is well. The question is, of course, WHY does the system think the device has been unplugged?

My guess is power, or a lack of it. USB devices can (and many times are) powered by the computer to which they are connected. This can include mice, scanners, keyboards, some printers, and more. The problem is that there are many situations where there is just not enough power to go around to all the devices. Each device on its own would have enough if it were the only thing connected to the computer, but plug everything in together and you can run into a problem. Enter what I believe to be the solution to this problem: the powered USB hub.

Many people use USB hubs to "add" ports to their computers. This is perfectly fine. Some hubs draw power from the computer (which means their connected devices also draw the computers power), while others, like the one from TechWorks (see "PowerUSB Hub, A Strong Offering From TechWorks"), give you the option of plugging the hub into A/C power. With this, the hub provides not only its own power, but power to the USB devices that are connected to it. My guess is that most of the people with this problem are running a ton of USB devices without any extra USB-bus power and that a powered USB hub would fix most, if not all, of these "mouse freezing" problems. The mouses (or is that mice?) are typically connected at the end of the chain (remember that the USB keyboard also acts as an unpowered hub here, too!), and there may be times when there's just not enough power to make it all the way out there and back. When this happens, the system thinks the device has been disconnected and unloads the drivers.

I'd appreciate any comments or feedback on this issue from those out there "testing" in the field! Either e-mail me at [email protected] or post to the Ask Dave Forums!

P.S. Have a Nice Day.

is President and CEO of The Mac Observer, Inc. He has worked in the computer industry as a consultant, trainer, network engineer, webmaster, and a programmer for most of the last 10 years. During that time he has worked on the Mac, all the various Windows flavors, Be, a few brands of Unix, and it is rumored he once saw an OS/2 machine in action. Before that he ran some of the earliest Bulletin Board systems, but most of the charges have since been dropped, and not even the FBI requests that he check in more than twice a year.

Ask Dave is here to answer all the Mac questions you have. Networking, system conflicts, hardware, you ask it, he can answer it. He is the person from whom all Mac knowledge flows....

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