On 5/11/06, David Brownell <[EMAIL PROTECTED]> wrote:
On Thursday 11 May 2006 8:49 am, Christopher Montgomery wrote:
> (If so, the isos are occurring in totally random places in a given frame).
Nope. Periodic transfers take up the second 90% of the frame (at most).
And this doesn't have any scheduling conflicts with high speed transfers.
I didn't mean that in practice they occur 'in totally random places'
but that the spec allows this, and it is not a violation of the USB
1.1 for the iso transfer to end up in completely different parts of a
FS frame from frame to frame, eg the beginning of one and the end of
another. Again, I'm concerned with the FS frame first and fitting the
splits into the uFrame scheduling second, because things will nearly
always fit into the uFrame.
> The EHCI FS/LS sceduling should probably be aping the OHCI
> behavior as it's known to work well.
No; ohci-hcd does some "best fit" logic, which happens to be cheap for
that hardware. Whereas ehci-hcd uses "first fit", because it's costly
to do highspeed scheduling.
I don't mean we should emulate how the OHCI hardware is driven; I mean
that the end-result, the final produced FS frame produced by OHCI, is
efficient and that we should aspire to that level of efficiency in our
end result-- the FS frame produced by the TT.
The similarity is basic: see how much space is available, try the next
schedule point if this one doesn't have enough (in all schedule slots).
And that's already coded.
Except that the way it's broken up now, I can't get a 1Mbps iso in
transfer to work through the TT, when ohci can push/pull 9Mbps to this
specific device without hiccups. The current scheduler is putting at
least one and up to two full microframe-slots worth of holes between
every FS transaction, and when you have to fit three transactions into
a FS frame, you can see that it just won't fit. (to set up the iso in,
this device also needs two intr transactions to other endpoints).
For this to work, the holes have to go. Every hole is immovably
wasted bandwidth.
Monty
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