The Interval field of an endpoint context is an exponent: the controller
services the endpoint every 2^Interval microframes. An endpoint
descriptor states its period differently depending on device speed, so the
number cannot be copied across, which is what this did. A low speed
keyboard asking to be polled every 10ms was programmed as 2^10
microframes, which the controller would not accept: Configure Endpoint
went unanswered and allocation failed with -EIO.
Low and full speed interrupt endpoints state a period in frames, so the
exponent is the highest bit of that period in microframes, clamped to the
range the specification allows. Other periodic endpoints already state an
exponent, one greater than the one wanted here. Control and bulk
endpoints are not periodic and the field means nothing to them.
Assisted-by: Claude:claude-opus-5
Signed-off-by: Justin Hammond <justin@dynam.ac>
a11cecd100