On Sat, 15 Sep 2018, Alistair Buxton wrote:
> On 15 September 2018 at 21:11, Alan Stern <st...@rowland.harvard.edu> wrote:
> > On Sat, 15 Sep 2018, Alistair Buxton wrote:
>
> > Wrong -- bInterval is a maximum value only and the host is free to poll
> > more quickly.
>
> I can only say that real world testing contradicts this. Our device
> sets bInterval to 5. Linux polls it every 4 milliseconds, another host
> running a proprietary operating system polls it every 8 milliseconds.
> So it seems that in the real world the interval can be higher or lower
> than what you asked for.
Then that proprietary operating system is not in compliance with the
USB 2.0 specification. On p.51, the spec says:
The period provided by the system may be shorter than that
desired by the device up to the shortest period defined by the
USB (125 us microframe or 1 ms frame). The client software and
device can depend only on the fact that the host will ensure
that the time duration between two transaction attempts with
the endpoint will be no longer than the desired period.
Alan Stern
