>Sent: Monday, February 11, 2008 8:51 PM
>> Dear all:
>
>> 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?
>
>> I cannot find any information about "device address" in device descriptor
>> at chapter 9 of usb2.0 spec.
>
>The device address isn't part of the device descriptor. It is
>described in section 9.1 of the spec.
>
>> Since we can get endpoint address in endpoint descriptor and set the ep#
>> before controller determine where the data he sent out.
>> But how about device address?
>> Is this value randomly set by host when more than 1 device connected to it?
>
>The address is set by the host when more than 0 devices are connected.
>The values are not random; they are chosen sequentially: The first
>device has address 1, the second device has address 2, and so on.
>
>> 3. can 2 QHDs point to the same endpoint?
>> Ex: QHD[0]--> ep0
>> QHD[1]--> ep0
>
>No.
>
>> 4. if the answer of 3 is Yes, can we set different device address and
>> different maximum packet length on several QHs, which point to the same end
>> point.
>> Ex:
>> pQH[0]->bTerminate=0; //data is valid
>> pQH[0]->bType=0x01; //QH type
>> pQH[0]->bEp=0x00; //ep0
>> pQH[0]->uDeviceAddress= 0x00;
>> pQH[0]->uMaxPacketSize=0x08;
>>
>> pQH[1]->bTerminate=0; //data is valid
>> pQH[1]->bType=0x01; //QH type
>> pQH[1]->bEp=0x00; //ep0
>> pQH[1]->uDeviceAddress= 0x01;
>> pQH[1]->uMaxPacketSize=0x40;
>
>If the device addresses are different then the QHs don't refer to the
>same endpoint. In your example, pQH[0] refers to ep0 on device 0 and
>pQH[1] refers to ep0 on device 1 -- those are two different endpoints.
>
>Alan Stern
>
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