I am trying to write a usb device driver for an R5000 modified
set-top-box. This just adds a USB interface to the decoded signal from
a satellite STB so you can save whatever is currently being watched on TV.
I snooped the USB bus in Windows, and am able to upload the firmware and
communicate with the device just fine on endpoints 01 and 81. However,
retrieving the stream requires a high-bandwidth read on 82. If I do
this using blocking reads, the device never sends any data back It
appears to be waiting for multiple bulk request URBS in the queue. This
apparently eliminates my ability to use libusb, so now I need to do the
same thing in kernel-space.
modifying usb-skeleton I've got a kernel module that does all of the
requests, however, now I keep getting babble errors when the
read-completion returns (EOVERFLOW)
One thing I noticed is that endpoint 82 declares a max packet size of
0x400 where I thought the largest allowed size for usb 2.0 is 0x200.
The requests from Windows also have a buffer size of 0x20000, but I
assume the driver is splitting that into smaller packets.
I get the babble error regardless of the read-size I specify for the URB
request.
Ok, so that is all the background info.
I'm not sure whether I'm initializing something incorrectly, or if the
device is doing something odd. So I'm wondering if there is a way to
see the raw data that got returned for the URB even though it had a
babble error (I seem to always get a 0 len result, so I assume the
EOVERFLOW nukes whatever data might have been sent). this would help
determine where the problem lies.
Interestingly, the same libusb driver I did for linux (which can't read
the stream) works fine using win32-libusb on Windows. I'm assuming that
is a red-herring though, and has something to do with the Windows driver.
If it is useful, my read handler looks sort of like this:
urb = usb_alloc_urb(0, GFP_KERNEL);
buf = usb_buffer_alloc(dev->udev, readsize, GFP_KERNEL,
&urb->transfer_dma);
usb_fill_bulk_urb(urb, dev->udev,
usb_rcvbulkpipe(dev->udev, 0x82),
buf, readsize, skel_read_bulk_callback, dev);
urb->transfer_flags |= URB_NO_TRANSFER_DMA_MAP;
retval = usb_submit_urb(urb, GFP_KERNEL);
usb_free_urb(urb);
(there's a bunch of error checking and other stuff, but that's the guts
of it) I've tried all different values of readsize to no avail.
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