How to increase BUlk MaxTransferSize for a virtual usb HCD?

I have a virtual usb HCD driver(something like usb over IP). I am receiving max. 256KB transfer size(TransferBufferLengthon) on Bulk OUT endpoints from usb client drivers in Windows 7. Is there any way to increase the transfer size?

xxxxx@gmail.com wrote:

I have a virtual usb HCD driver(something like usb over IP). I am receiving max. 256KB transfer size(TransferBufferLengthon) on Bulk OUT endpoints from usb client drivers in Windows 7. Is there any way to increase the transfer size?

What kind of HCD do you emulate?

This is up to the individual client drivers. EHCI and UHCI HCDs allow
up to 4MB, but OHCI HCDs running at full speed are limited to 256kB, and
as a result some clients adopted that limit. The USB storage driver
gets its max transfer size from a registry entry; there are web hits
showing how to hack that value.

However, I’m wondering why you would care. In order to support audio
and video devices, you have to emulate the packet timing of a real HCD
pretty closely. It’s not clear to me what you would gain through larger
transfer sizes.


Tim Roberts, xxxxx@probo.com
Providenza & Boekelheide, Inc.