Hi Hans,

Thanks very much for your help. This mass storage device does indeed have wMaxPacketSize of 512.

(gdb) p *xfer->endpoint->edesc
$6 = {
  bLength = 0x7,
  bDescriptorType = 0x5,
  bEndpointAddress = 0x81,
  bmAttributes = 0x2,
  wMaxPacketSize = "",
  bInterval = 0xff

(gdb) x /xh xfer->endpoint->edesc.wMaxPacketSize
0x6dba0616:     0x0200

Thanks again,

On 13-02-08 06:01 PM, Hans Petter Selasky wrote:
On Friday 08 February 2013 22:48:02 aman.sawrup wrote:

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
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
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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