Re: FHCI driver adaptation for CPM2

[Laurent Pinchart <laurentp@cse-semaphore.com>]

Hi Remi,

On Wednesday 17 December 2008 21:27:49 Remi Lefevre wrote:
> >> Also 40% seems quite a lot, even at 1000Hz interruptions, an idea how
> >> much does the CRC computation contribute in this CPU hogging ?
> >
> > I haven't measured that, but probably not much. The biggest CPU time
> > eater isn't the SOF generation interrupt but the USB packet handling
> > code. The CPM2 USB host controller is really too low-level to be usable
> > (except maybe for specific applications). Comparing the OHCI/UHCI/EHCI
> > and FHCI controllers is akin to  bit like comparing a full 16550 UART
> > with a software bit-bang implementation. You can get around with it, it
> > might work for your specific application, but you shouldn't try a full
> > speed 115200bds communication while computing a CPU-hungry physical
> > simulation.
>
> That's what I was afraid of. I now understand clearly why you didn't expect
> that much better performance with CPM3 in a past message
> (http://ozlabs.org/pipermail/linuxppc-embedded/2008-May/030508.html).
> Still, as you said, it can have some use for specific applications.
>
> Do you remember the throughput you were able to reach with this cpu
> overhead ?

I'm sorry I don't.

Best regards,

-- 
Laurent Pinchart
CSE Semaphore Belgium

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