Ian Dowse wrote:
In message <[EMAIL PROTECTED]>, Hans Petter Selasky writes:
But there is one problem, that has been overlooked, and that is High speed
isochronous transfers, which are not supported by the existing USB system. I
don't think that the EHCI specification was designed for scatter and gather,
when you consider this:
8 transfers of 0xC00 bytes has to fit on 7 pages. If this is going to work,
and I am right, one page has to contain two transfers. (see page 43 of
ehci-r10.pdf)
I haven't looked into the details, but the text in section 3.3.3
seems to suggest that EHCI is designed to not require physically
contiguous allocations here either, so the same approach of using
bus_dmamap_load() should work:
This data structure requires the associated data buffer to be
contiguous (relative to virtual memory), but allows the physical
memory pages to be non-contiguous. Seven page pointers are provided
to support the expression of 8 isochronous transfers. The seven
pointers allow for 3 (transactions) * 1024 (maximum packet size)
* 8 (transaction records) (24576 bytes) to be moved with this
data structure, regardless of the alignment offset of the first
page.
yes, as long as the beffers are contiguous in some virtual space then
the maximum number of pages they
can need is 7.
(they actually fit into 6 but they may start part way through the first
page and may therefore overflow into a 7th).
Ian
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