[Xenomai] RaspberryPi kernel 3.8 issue

Gregory Dymarek gregd72002 at gmail.com
Sun Mar 2 22:03:21 CET 2014

3.10 does not require the USB patch. It just requires the the ealier patch
where local_fiq_* are defined as hard_local_fiq_*

When I searched the USB issue around the net I found the explanation for
using FIQ in USB driver on this board:

"the Synopsys driver relies on the start of frame interrupt for scheduling
transfers if "descriptor DMA" is not implemented (which it isn't, on
BCM2835).  8000 is one interrupt per microframe."

A solution in 3.8 was to use FIQ for USB IRQs to discard USB microframes
that contain no data.

All clear now. Thanks Gilles.

On 2 March 2014 19:08, Gregory Dymarek <gregd72002 at gmail.com> wrote:

> Understood. I will have a look.
> I'll be getting kernel 3.10 in a moment. It looks like USB driver is
> different to the one in 3.8.
> Will see what it does.
> Overall, there has been a lot of debate around the USB driver on this SOC
> so you might be right that the driver is not working as it is supposed to.
> Not yet at least.
> On 2 March 2014 19:04, Gilles Chanteperdrix <
> gilles.chanteperdrix at xenomai.org> wrote:
>> On 03/02/2014 07:57 PM, Gilles Chanteperdrix wrote:
>> > On 03/02/2014 07:54 PM, Gregory Dymarek wrote:
>> >> This works!!
>> >>
>> >> I thought xenomai does not deal with fiq. Why is it required to enable
>> them
>> >> in the driver when having xenomai on?
>> >
>> > Because without CONFIG_IPIPE local_irq_restore deals with FIQs
>> > With CONFIG_IPIPE local_irq_restore does not deal with FIQs
>> >
>> > We can of course rework local_irq_restore to take into account FIQs with
>> > CONFIG_IPIPE, but that would make local_irq_restore heavier in a lot of
>> > places, whereas there are in fact only three spots to fix, for only one
>> SOC.
>> >
>> >
>> BTW, using FIQs for USB means that USB activity will be able to
>> influence xenomai latencies. So, it is really not recommended, if there
>> is a configuration option for disabling the use of FIQ with this driver,
>> this should be recommended for use with xenomai.
>> --
>>                                                                 Gilles.

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