[Arm-netbook] Arm Netbook, Saw the update,

[Luke Kenneth Casson Leighton]

On Tue, Jul 4, 2017 at 4:15 PM, Richard Wilbur <richard.wilbur at gmail.com> wrote:
> On Jul 4, 2017, at 02:27, Luke Kenneth Casson Leighton <lkcl at lkcl.net> wrote:
>>
>> ok richard i've redone the layout, and published 3 images here:
>> http://rhombus-tech.net/allwinner_a10/news/
>
> Thanks for letting me know.  I took an initial peek at the images and they look like you addressed the points I mentioned.

 yay

> I'm going to be a day or two getting back with more detailed questions as today is a holiday here and we have family visiting till Thursday.

 nice

> A couple questions that spring immediately to mind:
> 1.  How continuous are the ground planes under the differential pairs?  (Are there voids in the ground planes under the differential pairs?)

no.  layers 2 and 5 are solid ground planes.  vias obviously go
through those , full vias only.  non-GND vias also obviously create
small interruptions but that's all

> 2.  The intra-pair length sounds well-matched, my understanding of the inter-pair skew is that the requirement is in terms of the clock speed Δt <= 0.2 Tcharacter.  For 225 MHz clock the application note spoke of 888ps.  So we'll be interested in determining the maximum clock rate and speed of propagation.

 3e8 m/sec * 888e-12 = 0.2664 metres.... which is 266.4 mm... way
beyond anything which would indicate some kind of problem if the board
is 78mm long and the skew is only 2mm.

> I'll also have some questions about dimensions and geometry.

 ack.

> Thank you for the opportunity to participate.

 always appreciate the help.

l.