Re: FHCI driver adaptation for CPM2

["Remi Lefevre" <rlefevre@gmail.com>]

> Hi Remi,

Hi Laurent,

> You will find my latest version of the CPM2 FHCI patch attached to this e=
-
> mail. I've never bothered to clean it as we decided to drop the USB host
> function from our device.

Thank you very much. Not clean is better than lost.

> This depends on the disk. Some will probably not check the SOF token, oth=
ers
> will do and behave strangely.
>
>> Also 40% seems quite a lot, even at 1000Hz interruptions, an idea how mu=
ch
>> does the CRC computation contribute in this CPU hogging ?
>
> I haven't measured that, but probably not much. The biggest CPU time eate=
r
> 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 fo=
r
> 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 specif=
ic
> application, but you shouldn't try a full speed 115200bds communication w=
hile
> 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 overhea=
d ?

> Laurent Pinchart
> CSE Semaphore Belgium

Kind regards,
R=E9mi Lef=E8vre