Hi Remi,

On Wednesday 17 December 2008 21:27:49 Remi Lefevre wrote:

quoted

quoted

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

Chaussee de Bruxelles, 732A
B-1410 Waterloo
Belgium

T +32 (2) 387 42 59
F +32 (2) 387 42 75