some question about ehci-sched.c

[yoma sophian]

hi all:
in iso_stream_schedule of ehci-sched.c, why we have to add the "-" in
(-(++ehci->random_frame))  to calculate the start uframe?
thanks for ur help in advance.

                if (stream->ps.phase == NO_FRAME) {
                        int             done = 0;
                        struct ehci_tt  *tt = find_tt(stream->ps.udev);

                        if (IS_ERR(tt)) {
                                status = PTR_ERR(tt);
                                goto fail;
                        }
                        compute_tt_budget(ehci->tt_budget, tt);

                        start = ((-(++ehci->random_frame)) << 3) & (period - 1);
                                      ^^ Here it is.