From mboxrd@z Thu Jan  1 00:00:00 1970
Message-ID: <47162E66.1080406@domain.hid>
Date: Wed, 17 Oct 2007 17:46:46 +0200
From: "CHABAL David" <david.chabal@domain.hid>
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Subject: Re: [Xenomai-help] awful latencies (~110us)
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To: rpm@xenomai.org
Cc: xenomai@xenomai.org

Philippe Gerum a =E9crit :
> On Wed, 2007-10-17 at 16:52 +0200, CHABAL David wrote:
>>> Grmmff... I think the PIC on this box has some deep troubles; please =
try
>>> this patch, in replacement of the previous ipipe_trace_special
>>> instrumentation:
>>>
>>
>> RTD|       8.348|      10.387|      43.647|       0|       6.098|=20
>> 80.440
>> ---|------------|------------|------------|--------|------------------=
-------
>> RTS|       6.098|      10.020|      80.440|       0|    00:17:20/00:17=
:20
>> [root@domain.hid bin]#
>>
>>
>> IRQ handling takes 17=B5s in the worst case.
>>
>> It takes a long time to write 3 poor bytes...
>>
>=20
> Indeed. Each outb to the ISA bus should be somewhere in the 1-2.5 us
> range depending on the hw, maybe a bit higher in case of contention, bu=
t
> not that much.
>=20
>> May be is it a SMI problem ??? (Globally disable SMI is on)
>>
>=20
> It's less likely with an ICH-2 chipset.
>=20
> I see that CONFIG_IDEDMA_PCI_AUTO is disabled. Any reason not to use PC=
I
> DMA when available for IDE drives with your hw?
>=20

I read this about DMA:
http://www.rtai.dk/cgi-bin/gratiswiki.pl?DMA_And_Jitter

but I'm not sure if I understood well.

David