[Arm-netbook] EOMA-200 30W module standard

[Dr. David Alan Gilbert]

* luke.leighton (luke.leighton at gmail.com) wrote:
> moving forward from the EOMA-68 standard, which has a maximum limit of
> around 3.5 watts, we felt that a larger more power-intensive standard
> should be created, and have begun a preliminary draft:
> 
> http://elinux.org/Embedded_Open_Modular_Architecture/EOMA-200
> 
> as with all EOMA standards, there are NO and there will never be ANY
> optional pins.  to compensate for differences in CPUs, SoCs and
> designs however, the front-face of the module is permitted to have any
> number connectors that will fit into the two slots - 30mm x 14mm and
> 65mm x 14mm.

Some thoughts and questions:
  1) I'm not sure I'd have gone for specifiying quite as much backward compatibility;
do you really need to specify that it can do 10Mbpps/etc - I think it might
be reasonable to put a higher constraint; i.e. it must support 100Mbps
with support for anything below it being optional.

  2) Does the ethernet interface do auto crossover? It's a required feature of GigE
interfaces and is implemented by some implementations at lower speeds.

  3) I'm not sure the PCIe is specified strongly enough; is it required that
on a device which provides 4 lanes that it can be used as 4 separate interfaces?
(or 2x2 or 3 as 2x1+1x2 ?) Does the card always provide a PCIe host interface?
Are there minimum address space guarantees I can rely on? I don't know enough PCIe
to know what else it needs to ask for but I suspect there is some more.

  4) I'm not sure it's that helpful to specify the PCIe is a requirement but
then suggest bodging on a USB->PCIe bridge to make use of a SoC that doesn't
have real PCIe; in many designs the card would be useless - imagine a 
chassis that had put all it's interesting devices on PCIe (maybe a fast graphics
card/storage controller etc) - and then gets a CPU that's actually connected
via a USB connector - so in terms of selecting an EOMA card you'd find that
your choice of card was correct but useless.

Dave
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