Dave:
Thanks a lot for all your explanation. But I still have some questions.
On Monday 03 April 2006 5:32 am, Ethan Du wrote:
>
> > > The only difference is ECM extended a data class
> > > interface. EEM doesn't. Is this the benefit of EEM? And is it more
> > > efficient using less interfaces?
> >
> >If you look at EEM, it's clearly a bit less demanding than ECM in terms
of
> >hardware; it can work without altsettings. (The interrupt/status
endpoint
> >is optional for ECM.) Which means there's more choice for peripheral
> >hardware.
> >
>
> Do you mean EEM is saving endpoints?
No; as I said, it's less demanding because it doesn't need altsettings.
I know the Data Class interface of a networking device shall have a minimum
of two interface settings. Do you mean this?
> Or could you explain the relationship
> between altsettings and hardware.
There's no need for such a relationship, but some controllers try
to move such software policies into the hardware. Examples include
the pxa25x and pxa27x controllers from Intel, both of which make it
quite painful (or impossible) to use altsettings.
I checked the datasheet of pxa27x, and found that it supports 7 alternate
setting for each interface. I also checked the datasheet for ISP1583, it
doesnt move alternate setting to hardware (register). So, I think even move
the alternate setting policy to hardware, the number of alternate setting is
big enough, so it is not a big deal of saving alternate setting, is it? So
whats the real purpose of EEM?
And will CDC Ethernet waste time interpreting data coming from data class
interface, comparing to EEM?
Thanks.
Ethan.
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