Re: MPC8313 performance evaluation

[Lutz Jaenicke <ljaenicke@innominate.com>]

On Fri, Aug 07, 2009 at 04:08:50PM +0800, Liu Dave-R63238 wrote:
> 
> > Some discussion with the the freescale rep. lead to the CSB frequency
> > of the 8313 (166MHz) being significantly lower than that of the 8343.
> > Is the CSB the critical point here?
> 
> I believe the CSB is critical point here. They are right.

I have performed some additional measurements with other multiplier/divider
settings 

Previous values with CSB=166MHz
> >> With the MPC8313 I get a significantly lower value:
> >> MPC8313@250MHz          12500fps
> >> MPC8313@333MHz          14500fps
> >> MPC8313@416MHz          15500fps      (333MHz type, overclocked)

New value with CSB=200MHz (overclocked)
     MPC8313@400MHz          17500fps

This indeed indicates that the CSB is the limiting factor.
Until a few days ago I have not even been aware of the CSB being a
performance critical component. All of the nice powerpoints explaining
the processors and used for comparing different families shown by the
Freescale Rep include the core frequencies and the DRAM interface
and frequency but do not even mention the CSB...

> > Note: the IXP42x uses an internal bus speed of 133MHz and operates
> > at frame rates similar to the 8343...
> 
> It is possible, IXP42x has the differenet SoC architecture with 83xx.

That is very true indeed, then XScale (ARM) based IXP42x does have
a completely different implementation.

Best regards,
	Lutz
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Dr.-Ing. Lutz Jänicke
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