From: David Brownell <[EMAIL PROTECTED]> To: fengwei yin <[EMAIL PROTECTED]> CC: [EMAIL PROTECTED], [EMAIL PROTECTED] Subject: Re: [linux-usb-devel] get hub port status on big endian board Date: Tue, 18 May 2004 06:26:03 -0700
fengwei yin wrote:I need guidance About the TD queue processing.
Let me take usb_set_address as example.
Before TD queue processing,the TD queue as following: TailP | | V HeadP---->dummy TD------>td[0]------>td[1]
Erm, no. It should be
HeadP -> td[0]/SETUP -> td[1]/STATUS -> dummy TailP -> dummy
kernel 2.4.x Sorry,I can't find where HeadP is set to td[0].
In function ep_add_ed:
td = td_alloc (ohci, SLAB_ATOMIC);
...
ed->hwTailP = cpu_to_le32 (td->td_dma);
ed->hwHeadP = ed->hwTailP;
Before queue processing,never touch ed->HeadP. So I think ed->HeadP --> dummy.
In function td_fill: td_pt = urb_priv->td [index]; td_pt->hwNextTD = 0;
td_fill will be called with index=0,1(td[0],td[1]). When index=1,td[1]->Next=0. So I think td[1] is the last element of list.
After TD queue processing,the queue as following:
HccaDoneHead---->td[0]----->dummy TD
Then
HeadP -> dummy TailP -> dummy
which is to say, an empty queue. And if no other endpoint was working, the donelist would be
hcca DoneHead -> td[1] -> td[0] -> NULL
Which is why the donelist gets reversed (to td[0] then td[1]) before it's processed.
- Dave
Regards yfw
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