On Friday 08 February 2013 22:48:02 aman.sawrup wrote:
> Hello,
> We have ported the FreeBSD USB stack to my employers proprietary RTOS.  The
> code was taken from the MAIN branch a little while after RELENG_8_BP tag
> was created.
> I'm trying to read data from the following mass storage device umass0:
> usbus0: EHCI version 1.0
> usbus0: 480Mbps High Speed USB v2.0
> ugen0.1: <Intel EHCI root HUB> at usbus0
> uhub0: <Intel EHCI root HUB, class 9/0, rev 2.00/1.00, addr 1> on usbus0
> uhub0: 2 ports with 2 removable, self powered
> ugen0.2: <vendor 0x8087 product 0x0024> at usbus0
> uhub1: <vendor 0x8087 product 0x0024, class 9/0, rev 2.00/0.00, addr 2> on
> usbus0
> uhub1: 8 ports with 8 removable, self powered
> ugen0.3: <ATP Electronics ATP IG eUSB> at usbus0
> umass0: <ATP Electronics ATP IG eUSB, class 0/0, rev 2.00/11.00, addr 3> on
> usbus0
> umass0:  SCSI over Bulk-Only; quirks = 0x4800
> Reading data one frame per transfer works.  For example, if I want to read
> 512 bytes that is physically contiguous and is placed in a single frame,
> that works fine.
> However, when attempting to read 1024 bytes, that is not physically
> contiguous, using 3 frames for the same transfer, I get USB_ERR_STALLED.  I
> have the frames setup as follows:
> frame[0] = 200 bytes
> frame[1] = 512 bytes
> frame[2] = 312 bytes


The frame lengths must be a multiple of the wMaxPacketSize (typically 64 or 
512). Each frame is encoded like one or more USB packets independent of the 
next one. I.E. USB packet data may not cross a frame. This is not supported by 
the EHCI/OHCI and UHCI hardware, and the USB stack will not make a fixup 
buffer for this. The USB stack returns the device independent multiplier 
length for this purpose when calling usbd_xfer_max_framelen(). Only when 
(frame[n] % usbd_xfer_max_framelen() == 0) it will work like you want.

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