Hi Ilyes, you won't be able to allocate that much *contiguous* memory, but you should be able to allocate enough non-contiguous memory (e.g. by calling __get_free_page 256 times; not the same as calling __get_free_pages(8) !). To use that memory, you can try using the usb scatter/gather support (see usb.h); I don't know if it works with isochronous urbs though. I've CC'd the usb development list - maybe someone there can help.
Ciao, Duncan. On Saturday 25 November 2006 21:42, Ilyes Gouta wrote: > Hi! > > I'm working on a driver for my USB 2.0 high-speed webcam under Linux > and I'm using a tool > called usbsnoop, which was designed for Windows, to get an idea on the > exchanged > information between the host and the webcam. By examining the produced > trace file, I found > that my PC is sending a bunch of isochronous URBs to the webcam where > each one contains > 256 isochronous packets and each packet is 3072 bytes wide. This means > that every URB > points to a 256 * 3072 bytes sized buffer. > > Here is an excerpt of the trace file: > > [21303 ms] >>> URB 1640 going down >>> > -- URB_FUNCTION_ISOCH_TRANSFER: > PipeHandle = ff27dd8c [endpoint 0x00000081] > TransferFlags = 00000005 (USBD_TRANSFER_DIRECTION_IN, > ~USBD_SHORT_TRANSFER_OK, > USBD_START_ISO_TRANSFER_ASAP > TransferBufferLength = 000c0000 > TransferBuffer = fd319100 > TransferBufferMDL = 00000000 > StartFrame = 00000000 > NumberOfPackets = 00000100 // in hex > IsoPacket[0].Offset = 0 > IsoPacket[0].Length = 0 > IsoPacket[1].Offset = 3072 > IsoPacket[1].Length = 0 > IsoPacket[2].Offset = 6144 > IsoPacket[2].Length = 0 > > I tried to program this behavior in my custom, alpha stage, kernel > driver, however I was > disappointed since Linux fails to allocate, using kmalloc(), such a > huge buffer (which is > quite normal actually) to associated to the URB through the > transfer_buffer field. I also > tried __get_free_pages(GFP_KERNEL, 10) without any success whatsoever. > > Splitting the transfer across multiple URB doesn't seem to work (I didn't > really > investigate in depth this possibility). > > Any ideas? > > Thanks for your time! > > P.S: Is it possible to CC me since I didn't subscribe to the mailing > list? Thanks! > > Best regards, > Ilyes Gouta. > - > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to [EMAIL PROTECTED] > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ > ------------------------------------------------------------------------- Take Surveys. Earn Cash. Influence the Future of IT Join SourceForge.net's Techsay panel and you'll get the chance to share your opinions on IT & business topics through brief surveys - and earn cash http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV _______________________________________________ linux-usb-devel@lists.sourceforge.net To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-devel
