On Fri, 14 Nov 2003, ron ta�eza wrote:
Hi,
I'm using v2.4.18 (Slackware 8.1) and usb-uhci.
...
1. I'd like to write some data to the bulk out endpoint. If wMaxPacketSize is 64, and I'd like to write, say, 200 bytes, can I just set the urb's buffer_length to 200? Does the USB core automatically segment the data to 64-
byte chunks?
Yes.
2. Is the same with interrupt out?
Yes.
You're thinking of 2.6 there ... on 2.4, not all HCDs support interrupt transfers of more than one packet (either direction).
But on 2.6, bulk and interrupt transfers should be identical in almost all aspects except that interrupt transfers involve reserved bandwidth. Much simpler.
I also have a question on the USB specs. What's the difference between data0 and data1? I read something that data0 is even, and data1 is odd.. what does this mean?
It's a technique used for verifying that packets have been received correctly. .... The host normally alternates between DATA0 and DATA1 PIDs. ...
And data toggling is used for all USB transfer types except those related to isochronous transfers:
- iso packets themselves have no retry mechanisms - for synchronization, they can use a "no-toggle" interrupt transfer.
Linux doesn't really do much with that no-toggle interrupt transfer mode. Maybe it should someday.
- Dave
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