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

[Adrian Chadd]

Nah, we fixed it in mips. there's dirty, dirty assembler in the
exception handlr and idle loop calls to skip over the idle loop if an
interrupt comes in.



-a


On 10 May 2014 23:24, Hans Petter Selasky <hps at selasky.org> 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
>
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