Borchers, Al (C)(STP) wrote:
How should the interval field in an urb for USB 2.0
interpretted?  Is it microframes (125 micro-seconds)
as the ehci code seems to assume?   Or should it be
interpretted like the bInterval field in an endpoint
descriptor?

In the urb, it's never a logarithmic encoding; it's always frames or microframes. bInterval is logarithmic except for full speed interrupt transfers.


NOTE: I am still trying to get USB 2.0 interrupt transfers working for me
in 2.4.20 and .22.  I have not had time to track down the problems beyond
this issue with how the interval is interpretted.  For now I put my device
behind a 1.1 hub to fall back to 1.1 where interrupt transfers are working
fine for me.

The general rule of thumb is that full (and low) speed transfers haven't changed interpretation -- except that as of 2.6, full speed iso periods may be multiple frames. High speed is (as above) in microframes.

If you have a driver for a dual-speed device, the
driver needs to pay attention to high speed interrupt
transfers.

- Dave




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