[Arm-netbook] HDMI High-Frequency Layout: Recommendations

[Richard Wilbur]

On Aug 18, 2017, at 20:13, Luke Kenneth Casson Leighton <lkcl at lkcl.net> wrote:
> 
> On Fri, Aug 18, 2017 at 5:51 PM, Richard Wilbur
> <richard.wilbur at gmail.com> wrote:
> 
>> You bring up an interesting point:  what other current return paths are in the same vicinity?  I have not analyzed that in any detail.  At least there are no other lines from signal source to signal sink that I know of that cross the region of the board where the high-frequency HDMI signals are routed.  Also, to my knowledge we don't have segmented or restricted ground planes that would isolate regions with a higher-impedance reference.
> 
> CEC etc. all follow roughly the same path, on layer 3 (separated by GND).
> 
> i just noticed that SD0 runs round the back of the HDMI 1st set of
> VIAS (with no GND separation) on layer 3 - i've removed the SATA power
> (not being used) so i can shift them up a bit
> 
> some GPIOs cross on layer 3 as well, just near the GND shielding near
> those first vias...
> 
> not much.

Layer 3 always has ground separation from layer 1 in the intervening ground plane on layer 2 and likewise from layer 6 by layers 4 and 5.  So I'm not worried about those signals.

Regarding the SATA power:  Is it an important part of providing a SATA interface?  If so, I would suggest not limiting our options on this card.  My understanding is that SATA is significantly more efficient for harddisk data interface than USB.

Regarding SD0:  To what interface does it belong?  What is the maximum data rate on this line?