Re: [Libusb-devel] OpenUSB: max_xfer_size for control xfers

[Alan S. <st...@ro...>]

On Thu, 26 Jun 2008, Lei Chen wrote:

> > Actually, a control pipe is limited to 64 bytes per packet, so what
> I see that. In Solaris, the ehci driver allocates one qTD with one 
> page(4096 bytes) of memory for the control data. If client driver or 
> applications require less data than 4096 bytes, that's ok and the 
> underlying driver will deliver required length of data in one time to 
> upper layer. In this process, it may involve multiple packets to fill 
> that block of memory. In fact, host controller has splitted long data 
> into 64-byte packets. If more than 4096 bytes are required, an error 
> will be returned. Does Linux have similar behavior?

The EHCI and OHCI host controller drivers have a similar limitation on 
the length of control transfers.  The UHCI driver doesn't.

Alan Stern