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1. #How many devices can usb bt400 support Pc#
2. #How many devices can usb bt400 support plus#
3. #How many devices can usb bt400 support series#

If 3 fully populated USBHub3+ hubs are connected, 99 endpoints would be used with 24 typical USB devices. We need to tally up the total number of active endpoints (assuming 3 endpoints for each downstream device - input, output, control) to determine how many USBHub3+ hub ports can be used:ġ Acroname USBHub3+ (9 endpoints) + 8 Downstream Devices (8 x 3 = 24 endpoints) = 33 endpoints Going back to the previous example of the commonly available Intel XHCI-based host system, the integrated controller supports a maximum of 96 endpoints. Each hub chip defines one control endpoint, and the BrainStem controller itself adds 3 more endpoint, for a total of 9 endpoints per USBHub3+. Given these 3 internal hub chips, each USBHub3+ adds 2 tiers to the USB tree. Remember that each hub chip itself contains a USB 2.0 and a USB 3.0 device which will be added to the system USB tree. You can now see that each USBHub3+ unit is actually comprised of three hub chips in two internal hub layers: Hub A on one layer and Hub1/Hub2 on a second layer. USBHub3+ is no different and we can see this architecture clearly in the USBHub3+ datasheet: Each individual hub chip contains both a USB 2.0 device as well as a USB 3.0 device. USB Limits and the Acroname USBHub3+Īrchitecturally, 8-port USB hubs implement their 8-port configuration by internally cascading 2-port and 4-port USB hub chips. This will even furhter reduce the number of devices which can be attached to a single XHCI host controller. USB 3.0 devices may implement endpoints on both the USB 3.0 and 2.0 buses. That is, they live in the similar yet separate tree architecture in parallel with USB 2.0 devices, but they share the same endpoints on XHCI controllers. To make matters worse, USB 3.0 buses live in a strange dual existence with USB 2.0 devices.

This is a known limitation of Intel-based XHCI controllers:

#How many devices can usb bt400 support series#

The most notorious of these Intel's series 8 architectures. This means that the maximum number of common devices which use 3 endpoints able to be attached to an Intel series 8 XHCI host controller is actually 96 endpoints / 3 endpoints per device = 32 devices. The XHCI specification allows for a massive 7,906 enpoints! However, common implementations of the XHCI controllers impose their own limit on the total number of endpoints to 96. Most modern USB 3.0 hosts use eXtensible Host Controller Interface (XHCI) USB controllers. Every USB controller implementation may have its own layer or endpoint limitations. Hubs themselves also define at least a control endpoint. data in, data out, and a control endpoint). Defining USB EndpointsĮach USB device can define up to 32 endpoints (16 inputs and 16 outputs though one must be a control endpoint), but most devices only define 2 or 3 endpoints (e.g. Keep in mind that many low-cost USB expansion cards just add an internal hub. Thus, the ability to daisy-chain external hubs is reduced on a host machine that uses internal hubs. So, it is possible that the USB connector on your host machine is already one or even two tiers deep in the overall USB tree: What is not commonly known is that many host machines use hub chips internally to expand the number of available USB connectors. We have expanded the diagram to expand on the USB section, showing the USB Type A connectors:

#How many devices can usb bt400 support Pc#

Here, you can see a diagram of a typical PC architecture. Most host systems have just one USB controller that is integrated in the host system chipset. Therefore, for there is a hard limit of 5 daisy-chained hubs (not counting the root hub). The USB specification is limited to a maximum of 7 tiers.

#How many devices can usb bt400 support plus#

The tier number for any USB device is the number of non-root hubs in the connection chain plus 2. The host and root hub reside on the first tier, and a connection to a hub adds another tier. The USB 2.0 specification (section 4.1.1, figure 4-1) includes the following diagram to illustrate USB topology. USB tiers result from the use of hubs, where each hub is, in fact, its own USB device as well as the start of a new layer of USB devices.

Note that endpoints are not the same thing as devices. The USB specification defines two different connectivity types in the USB tree topology: number of layers or tiers and number of endpoints or functions. Let's take a deep dive to understand where this limitation comes from: As it happens, this is not a limitation of USBHub3+ itself, but rather a limitation of the host USB controller and the host machine's implementation of the USB controller. Some customers who have been using multiple Acroname USBHub3+ hubs have shared with us that they cannot add more than two USBHub3+ hubs to their system or that they need more USB resources.