Re: usb printer driver and zero length transfer

[Greg KH <greg@kroah.com>]

On Mon, Mar 24, 2003 at 11:51:50AM -0800, Kallol Biswas wrote:
> Hi,
>      I am new to USB world and looking for clarification on usb
> printer's
> behavior when transferring data with size  multiple of  wMaxPacketSize.
> 
> I have been running redhat 7.1 (linux kernel 2.4.2-2) on x86 PC with a
> USB 1.1 controller. There is a target mode printer driver running on the
> 
> other side.
> 
> On the host the device file is /dev/usb/lp0.
> If a data packet of 64 bytes is sent with
> 
> "cat data8 > /dev/usb/lp0" , the size of data8 is 64, a zero length
> packet
> at the end of the transfer is not sent.
> 
> Is this a correct behavior?  How do we force the printer driver send
> a zero length packet at the end of a transfer if the packet size is
> a multiple of wMAxPacketSize?

If your device requires that a zero length packet be send for this
situation, then modify the transfer flags of the urb with
URB_ZERO_PACKET to cause this to happen.

Hope this helps,

greg k-h