Vichy >Sent: Thursday, February 14, 2008 1:35 PM > >Dear all: >I list the initial sequences that I observed from source code. >If I get something wrong, please let me know. > >Suppose I get 3 devices connected to a host, A, B and C. >A plugs in. >We use QH with device-address = 0, ep = 0 to get A's device descriptor. >Set A's device address to 1. > >B plugs in. >We use QH with device-address = 0, ep = 0 to get B's device descriptor. >Set A's device address to 2. > >C plugs in. >We use QH with device-address = 0, ep = 0 to get C's device descriptor. >Set A's device address to 2. > >So Qh with device-address = 0, ep = 0 is always the default and least QH to >get every device's device descriptor, right?
Each URB will have an endpoint EP, each EP will have "one" QH associated with it when URB is submitted and the QH will have multiple transfer descriptors dynamically created as per the request. Now its it's a control EP0 URB, a QH would be created with Address=0 and tds with setup token etc. > >Appreciate your help, >vichy > >-----Original Message----- >From: Alan Stern [mailto:[EMAIL PROTECTED] >Sent: Tuesday, February 12, 2008 1:44 AM >To: Pandita, Vikram >Cc: vichy; linux-usb@vger.kernel.org >Subject: RE: Some Questions about QHD > >On Mon, 11 Feb 2008, Pandita, Vikram wrote: > >> >> 2. What is the "device address" used for in QH? >> > >> >There is no "device address" field in a QH -- at least, there isn't in >> >uhci-hcd or ehci-hcd. Maybe other controller drivers do have such a >> >field. >> >> I have a doubt - >> Referring to ehci spec 3.6, looks like the QH has a Device Address that >gets tracked in qh->hw_info1 field. >> >> Refer - >> qh_make ( >> ... >> info1 |= usb_pipeendpoint (urb->pipe) << 8; >> info1 |= usb_pipedevice (urb->pipe) << 0; >> ... >> qh->hw_info1 = cpu_to_hc32(ehci, info1); >> ... >> >> Isn't the QH identifying the destination pipe by an Endpoint Number + >Device Address? > >Yes, you are right and I was wrong. > >The EHCI controller uses the device address field in the QH to store >the value for the ADDR field of Token packets (see section 8.3 and 8.4 >in the USB 2.0 spec). > >Alan Stern - To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
