On Thu, 7 Dec 2006, Peter Stuge wrote: > On Wed, Dec 06, 2006 at 01:08:14PM -0800, Lu, Yinghai wrote: > > -----Original Message----- > > From: Andi Kleen [mailto:[EMAIL PROTECTED] > > Sent: Wednesday, December 06, 2006 12:59 PM > > > > >I haven't looked how the other usb_debug works -- if it's polled > > >too then it wouldn't have much advantage. > > > > Need to verify if the two sides of debug cable are identical.
In fact they are not. They are almost identical but not exactly the same. > I got my device yesterday and after a small plugfest I can confirm > that only one end of the device enumerates when connected to an ICH7 > EHCI driven by 2.6.19. This is incorrect. Both sides will enumerate. In fact, both sides will enumerate even at full speed (when plugged in to a UHCI controller instead of EHCI). The difference is that the device will accept power only from one side -- let's call it the A side (the side to the right when you have the PLX logo facing you). The device is bus-powered, so nothing will happen if the A side isn't plugged in. But if it is then both the A and B sides will enumerate. Their descriptors are almost the same; only the serial numbers are different. The A side's serial number string is "1", and the B side's serial number string is "0". Oddly enough, both sides use the same string index number for the descriptor (3). > Bus 001 Device 027: ID 0525:127a Netchip Technology, Inc. > Device Descriptor: > bLength 18 > bDescriptorType 1 > bcdUSB 2.00 > bDeviceClass 255 Vendor Specific Class > bDeviceSubClass 0 > bDeviceProtocol 0 > bMaxPacketSize0 64 > idVendor 0x0525 Netchip Technology, Inc. > idProduct 0x127a > bcdDevice 1.01 > iManufacturer 1 NetChip > iProduct 2 NetChip TurboCONNECT 2.0 > iSerial 3 1 ... > The device is in fact not self-powered. > > My theory is that the same set of descriptors are used for both ends, > but one end has been locked to address 127 in order to work with > simpler debug port drivers that assume it will be there. No, you are wrong. The device will accept any address on either side. > I guess that the self-powered error is also to simplify life for > debug port drivers. IIRC most if not all USB power management > concerns are noops for debug ports. I don't see how it would make life any simpler, but the device certainly does lie about its power source. Alan Stern - 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/