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Hardware limitations on USB endpoints (XHCI)


Hi all.

I would like to know how to find information about the number of endpoints that an intel device can support.

We currently use the C1107U and the J1900I-C

We prefer mini pc type setups for portability of our products.

[edit] I have also tested this on my Intel(R) Core(TM) i7-4770K CPU @ 3.50GHz and finding the same issue

We have noticed that windows 8 is able to support at least 18 connected devices, plus several hubs. We have noticed that Debian systems, however, have issues at about 12 devices and we see that the XHCI driver is reaching its endpoint limitation. We guess that this limitation is 64 endpoints (since hubs can consume 4 or 5 endpoints each)

I have spoken to the Linux kernal developers and they state that "Intel Ivy Bridge system xhci host, the 64 endpoint is a hardware limitation."

I have been able to disable the XHCI driver and force a rollback to the EHCI driver. This allows me to attach many more devices, but I am concerned that this is not a "safe" trick.

This also makes us concerned that the windows driver is may be cheating as well.

Our devices are all USB1.1

We run them on USB3 external powered industrial hubs.

Our devices are custom, so we can change the USB descriptors as necessary.

Currently we ask for (per device), 2 end points, less than 10mA and less than 12mb/sec.

so my Questions:

1. Is it "ok" to run EHCI, given the limitations observed in XHCI? Does EHCI have more endpoints? and why?

2. What options do we have to get more devices connected? We plan to further scale up our operations. For example "i5, i7" etc.


3. What do we need to look at in the chip-specifications in order to be able to know what the limitations actually are?

4. A lot of quick response to my questions regarding this matter have been "USB supports 127 connected devices" and "perhaps you are hitting a current limitation". Is this really true, given the above information?


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The system mentioned is an Asus MB: P7P55D-ELX with I5 core 650 @3.2 GHz running Win 10 Pro 32 bit OS on 64 bit system. The USB 3.0 is a Renesas VID 1033 PID 0194 host controller with 0.96 Microsoft driver.


Hello jlubeck

According to the data that you have provided you are using a Renesas µPD720200.

One suggestion that you could try is using a USB2.0 driver for a different Renesas controller to check if they are compatible with this product, or check with Renesas to see if they have an USB 2.0 driver for this controller.

This advice is mainly for Windows 7, I think from Windows 8.1 onwards, Windows uses xHCI controller by defualt even if no driver is installed.

Best Regards,

Adolfo Sanchez.