On Mon, 22 Sep 2003, David Brownell wrote:
> > Again, this case worked fine with the sd.c changes, so it does seem to be
> > all related to "big" transfers out of the mode page.
>
> Or at any rate, "big enough" to confuse the device.
Yes. Additional testing (making the code just increase the size of the
transfer until it fails) shows that a size of 63 still works, but a size
of 64 bytes fails.
Actually - with a 64-byte transfer, we appear to get the 64 bytes ok, but
the subsequent CSW status word read fails, so the 64-byte case seems to be
the one that starts confusing the device.
If I remember right, USB-1 "big packets" are 64 bytes in size, and a
64-byte bulk transfer would be two packets (one full-sized one, one
zero-sized one). So this seems to support the notion that the device is
fine as long as it can fit the whole bulk transfer in just one packet.
Which cleanly explains why EHCI "just worked".
Linus
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