[Xenomai] xenomai , irq and pci

Johann Obermayr johann.obermayr at sigmatek.at
Thu Mar 6 20:45:19 CET 2014

Am 06.03.2014 20:20, schrieb Gilles Chanteperdrix:
> On 03/06/2014 09:25 AM, Johann Obermayr wrote:
>> Am 05.03.2014 17:41, schrieb Gilles Chanteperdrix:
>>> On 03/05/2014 05:22 PM, Johann Obermayr wrote:
>>>> Hello,
>>>> celeron dual core with PCIe - PCI bridge
>>>> we use kernel 3.10.xx smp with  (isolcpus=0)
>>>> smi is disabled.
>>>> xenomai 2.6.3
>>>> we have a pci card with a fpga (with irq) and sram.
>>>> we have 2 task running.
>>>> task0 is one high prior in primary domain on core0.
>>>> this task wait for event, that is fired by fpga irq.
>>>> than this task will make some pci accesses to the fpga.
>>>> the other task (task1) is a shadow task, but running in secondary domain
>>>> on core 1.
>>>> This task make many big memcpy to sram.
>>>> in the ipipe_handler_irq we have a function callback.
>>>> a small driver hooks to this callback add make some tracepoint into
>>>> a shared memory.
>>>> with the trace we see some time a very high jitter in the ipipe_handler_irq
>>>> function (around 250 us).
>>>> has anyone an explanation for this?
>>>> and a 4 byte access from task0 to fpga need more than 300us,
>>>>     while task1 is writing to sram.
>>> Maybe the problem is the size of the PCI burst when writing to the SRAM?
>>> How large is it? If the sram is mapped with "write-combine", it will be
>>> buffered and written in large bursts. Maybe you could try mapping the
>>> sram area uncached?
>> Hi,
>> we use 2 real cores, no HT.
>> task1 do a memcpy with 10000 bytes.
> have you tried splitting the copy in smaller chunks, and use a mutex for
> exclusion between the two threads?
That can we do.
Only in our testsystem, but in customer application, we have no way to 
change this.
>> For mapping we use, rtdm_iomap_to_user
>> rval = rtdm_iomap_to_user(user_info, lv.phys_addr, lv.len, PROT_READ |
>> PROT_WRITE, &lv.virt_addr, NULL, NULL);
> You may want to try the following patch:
> http://git.xenomai.org/xenomai-2.6.git/commit/?id=1b8fb14e486ac0604e44067a0f1f89dc14153e95
we will test this.


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