[Arm-netbook] 2.7.4 preproduction sample, 1.7 MD, Questions

Luke Kenneth Casson Leighton lkcl at lkcl.net
Wed Jul 8 11:46:49 BST 2020

On Tue, Jun 16, 2020 at 9:45 AM Pablo Rath <pablo at parobalth.org> wrote:
> I have recieved an EOMA68-A20 2.7.4 preproduction computer card and the 1.7
> micro desktop (MD) last week. Just for clarification these boards are nothing new
> and have been discussed on this mailing list.
> If some of you already have their preproduction boards ready, I would
> appreciate any help, hints and suggestions to help me getting started.
> Altough I have some experience with handling arm-boards I am now afraid to do something
> **stupid** and break/fry the boards.
> After some digging in the list-archives I found this thread ([1]) where Richard and
> Luke discuss how to connect the bare computer card with the bare micro
> desktop.
> I have many questions:
> 1. Connecting computer card and micro desktop:
> I am aware of the photos attached to [2].
> Does the mentioned video exist?


> Richard, did you send photos to Luke? (If yes, can I have them?)
> Luke, do you want me to send you photos too before apllying power?

yes that would be good.  visually it is pretty obvious.  just do *not*
bend or waggle the Card as it's inserted (however you may find that
the connector is soldered at a slight angle of 1 to 3 degrees).

from visual inspection from the top, the gap left and right should be
equal.  this should be logically fairly obvious.

from visual inspection from the front, it should also be obvious if
the card has been inserted where the top row of pins has gone into the
bottom part of the connector or vice-versa.

If You Can See Pins You Got It Wrong.

also, once inserted, place the anti-static bag *in between* the Card
and the MicroDesktop PCB.

> 2. PSU for micro desktop:
> According to the mentioned thread ([1]): "5.5mm jack with a 2.1mm centre hole, middle is
> +ve (aka "pin positive")", "Anywhere between 7 and 21v is fine, minimum 1A, 1 5A is better"
> So I searched for a DC PSU in my household and read Wikipedia where it is
> mentioned that OD 5.5 mm / ID 2.1 mm is common on guitar effect pedals but my
> multi guitar effect pedal PSU did not fit (ID too small). Finally I found a
> matching DC PSU from a low volatage guitar amp. It says O / P: DC 15V, 2A and a symbol (positive polarity):
> L. P. S.
> - -(.- +

you're better off checking with a multimeter.  it's pretty standard
(pin positive) however there is no substitute for actually checking.
i.e.: don't guess - check.  hardware is unforgiving.

> So I think this should be good to go. Can anyone please confirm. Thank you.
> Should we document this somewhere on rhombus-tech.net?

yes, good idea.

> 4. SD-card ready / U-Boot
> Tried to compile u-boot-sunxi [4] and make exits with "System not configured".
> So Luke, what did you use as config

it's on the wiki somewhere.  it has been 5 years so i will be
searching just as much as you would be.

> or has something changed over the years?


> I also tried mainline U-Boot but could not find "EOMA68-A20-foo_defconfig"
> and "sun7i-eoma68-a20-foo.dts". What kind of defconfig and *.dts was used for
> the mainline U-Boot demos? My search of the mailing list archives and
> rhombus-tech was not futile. I could only dig up an old thread from 2014 where wookey was
> "assigned" to work on a minimal dts/dtb.
> 5. Git, notes and documentation
> Finally I am wondering where to put my notes. A subpage on rhombus-tech seems like a good idea
> good to me


> and indicates a work in progress in contrast to the various wikis
> out there. Where do you want me to push my work in progress git branches if I
> manage to hack something useful together?

i never needed to make any modifications to any linux kernel or u-boot
source code, so one has not been set up.


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