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

[Luke Kenneth Casson Leighton]

=On Sat, Jan 6, 2018 at 2:28 PM, Richard Wilbur
<richard.wilbur at gmail.com> wrote:
> On Jan 5, 2018, at 23:49, Luke Kenneth Casson Leighton <lkcl at lkcl.net> wrote:
>>
>> On Sat, Jan 6, 2018 at 6:35 AM, Richard Wilbur <richard.wilbur at gmail.com> wrote:
>>> So the trick is how to choose a faster chip and integrate successfully into a system running at lower speed than it is specified for?
>>
>> yyup.  have to use the 1800mhz 1.5v x8 DDR3 IC, which fortunately
>> happens to be down-compatible with 667mhz.  the 1.35v DDR3L variant of
>> the same chip is *not*.
>
> I was doing a little reading about DDR3 and noticed the 1.35V DDR3L memory chips are happy talking/running with 1.5V DDR3 systems.[1]  So are you saying the 1800mhz 1.35v x8 DDR3L IC is not happy running at 667MHz?  (Clock rate incompatibility versus voltage incompatibility?)

 correct.  the 1800mhz hynix 1.35v is specifically cut off from
supporting 667mhz and 800mhz modes.  this boards' DDR3 layout is...
not... exactly... great... but it works, as long as you don't go over
350mhz.

 funnily enough that turns out to be absolutely fine because four
DDR3x8 ICs running at 350mhz is abouuut.... half a watt or
thereabouts.  power consumption goes up on a square law so it would be
really bad to run much faster, even if it was possible.

l.