I also have USB hubs connected for various devices: printer, two external hard drives, webcam, camera, phone, iPod. It means I can move the laptop by disconnecting the power and one USB cable.
Is there a limit to what can be connected though one port? The XHCI specification allows for a massive 7, enpoints! However, common implementations of the XHCI controllers impose their own limit on the total number of endpoints to The most notorious of these Intel's series 8 architectures.
To make matters worse, USB 3. That is, they live in the similar yet separate tree architecture in parallel with USB 2. USB 3. This will even furhter reduce the number of devices which can be attached to a single XHCI host controller. Architecturally, 8-port USB hubs implement their 8-port configuration by internally cascading 2-port and 4-port USB hub chips. Each individual hub chip contains both a USB 2. Remember that each hub chip itself contains a USB 2.
Going back to the previous example of the commonly available Intel XHCI-based host system, the integrated controller supports a maximum of 96 endpoints. By removing one device 23 total , we would drop down to 96 endpoints. However, many host machines use USB internally for built-in peripherals, including webcams, touchscreens, and touchpads. Therefore, the number of external devices that can be connected is different for every system.
This number can be further impacted by a host machine where the USB connectors are already expanded by internal hubs. We've created a follow-up blog post with a suggested topology to reach maximum daisy-chaining potential. If you have lots of self-powered devices like printers and scanners , then your hub doesn't need to be powered -- none of the devices connecting to the hub needs additional power, so the computer can handle it.
If you have lots of unpowered devices like mice and cameras, you probably need a powered hub. The hub has its own transformer and it supplies power to the bus so that the devices don't overload the computer's supply. When the host powers up, it queries all of the devices connected to the bus and assigns each one an address. This process is called enumeration -- devices are also enumerated when they connect to the bus. The host also finds out from each device what type of data transfer it wishes to perform:.
As devices are enumerated, the host is keeping track of the total bandwidth that all of the isochronous and interrupt devices are requesting. They can consume up to 90 percent of the Mbps of bandwidth that's available USB 3. After 90 percent is used up, the host denies access to any other isochronous or interrupt devices. Control packets and packets for bulk transfers use any bandwidth left over at least 10 percent.
The Universal Serial Bus divides the available bandwidth into frames, and the host controls the frames. Frames contain 1, bytes, and a new frame starts every millisecond.
During a frame, isochronous and interrupt devices get a slot so they're guaranteed the bandwidth they need. Bulk and control transfers use whatever space is left. The technical links at the end of the article contain lots of detail if you'd like to learn more. The standard for USB version 2. USB 2. To allow a smooth transition for both consumers and manufacturers, USB 2. Supporting three speed modes 1. The deployment of USB 2. In addition to improving functionality and encouraging innovation, USB 2.
The USB 3. USB 3. It's meant for applications such as transferring high-definition video footage or backing up an entire hard drive to an external drive. As hard drive capacity grows, the need for a high-speed data transfer method also increases. Adoption of the USB 3. Additionally, the Allow the computer to turn off this device to save power check box does not appear on the Power Management tab for the USB root hub.
However, sometimes this feature may not correctly wake up the USB device. Therefore, the USB device is unresponsive when you try to use it. You might want to disable this feature for server products where power management is not important or required.
Important This section, method, or task contains steps that tell you how to modify the registry. However, serious problems might occur if you modify the registry incorrectly. Therefore, make sure that you follow these steps carefully. For added protection, back up the registry before you modify it. Then, you can restore the registry if a problem occurs. For more information about how to back up and restore the registry, click the following article number to view the article in the Microsoft Knowledge Base:.
If the DisableSelectiveSuspend registry entry is present, double-click it. If it is not present, create the entry. To create the entry, follow these steps:. Symptoms USB devices attached to the same hub are very slow or completely unresponsive.
Cause While multiple devices that are attached to the same hub are going into selective suspend, one of the devices on the hub can receive a wake request. Workaround Try these methods to work around this problem.
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