On Fri, 9 Oct 2009, Sarah Sharp wrote:
> @@ -1354,6 +1354,7 @@ iso_stream_schedule (
> period <<= 3;
>
> now = ehci_readl(ehci, &ehci->regs->frame_index) % mod;
> + next = now + ehci->i_thresh;
>
> /* when's the last uframe this urb could start? */
> max = now + mod;
> @@ -1365,13 +1366,15 @@ iso_stream_schedule (
> */
> if (likely (!list_empty (&stream->td_list))) {
> start = stream->next_uframe;
> - if (start < now)
> + if (start < next)
> start += mod;
>
> /* Fell behind (by up to twice the slop amount)? */
> if (start >= max - 2 * 8 * SCHEDULE_SLOP)
> start += period * DIV_ROUND_UP(
> - max - start, period) - mod;
> + max - start + ehci->i_thresh,
> + period)
> + - mod;
>
> /* Tried to schedule too far into the future? */
> if (unlikely((start + sched->span) >= max)) {
Sorry, what I wrote before wasn't quite right. This computation is
tricky. To check whether start is too small, you have to fit it into
the interval from next to (next + mod - 1). But then to check whether
it is too big, you have to fit it into the interval from now to (now +
mod - 1). And then in the end, you need to assign stream->next_uframe
a value between 0 and (mod - 1).
Since mod is always a power of two, the easiest approach may be
something like this:
next = now + ehci->i_thread;
...
start = stream->next_uframe;
/* Fell behind (by up to twice the slop amount)? */
if ((start - next) & (mod - 1) >=
mod - 2 * 8 * SCHEDULE_SLOP)
start += period * DIV_ROUND_UP(
(next - start) & (mod - 1),
period);
/* Tried to schedule too far into the future? */
if (unlikely(((start - now) & (mod - 1)) + sched->span
>= max)) { ...
}
stream->next_uframe = start % mod;
goto ready;
Alan Stern
--
To unsubscribe from this list: send the line "unsubscribe linux-usb" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
