USB isochronous traffic with Rasberry Pi [WAS: Re: USB audio device on Raspberry Pi]

[Ian Lepore]

On Sun, 2014-05-11 at 08:24 +0200, Hans Petter Selasky wrote:
> On 05/11/14 01:23, Ian Lepore wrote:
> > On Sun, 2014-05-11 at 00:25 +0200, Hans Petter Selasky wrote:
> >> Hi,
> >>
> >> This patch fixes the problem too:
> >>
> >> diff --git a/sys/arm/arm/machdep.c b/sys/arm/arm/machdep.c
> >> index 0490be7..8d53fab 100644
> >> --- a/sys/arm/arm/machdep.c
> >> +++ b/sys/arm/arm/machdep.c
> >> @@ -432,8 +432,12 @@ cpu_idle(int busy)
> >>                   cpu_idleclock();
> >>           }
> >>    #endif
> >> +       register_t s;
> >> +       s = intr_disable();
> >>           if (!sched_runnable())
> >>                   cpu_sleep(0);
> >> +       intr_restore(s);
> >> +
> >>    #ifndef NO_EVENTTIMERS
> >>           if (!busy) {
> >>                   cpu_activeclock();
> >>
> >> It appears some IRQ is happening when sched_runnable() is running, and
> >> then cpu_sleep(0) is executed even though sched_runnable() is no longer
> >> true.
> >>
> >> --HPS
> >
> > Aha!  Now I think you're on to something.  Even after explaining why
> > interrupts should be disabled for WFI I didn't notice that we don't
> > disable interrupts before WFI.  (I wonder if this is why I sometimes see
> > a lost timer interrupt and have to hit a key to un-wedge things.)
> >
> > Can you try the attached?  The spinlock_enter/exit calls are essentially
> > a combination of disabling interrupts and doing a critical_enter().
> >
> > -- Ian
> 
> Hi Ian,
> 
> Your patch works!
> 
> BTW: I see the "mips" platform might have a similar issue.
> 
> --HPS

Committed as r265913; thanks for tracking this down!

-- Ian