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

Pablo Rath pablo at parobalth.org
Tue Jun 16 09:44:47 BST 2020

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
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?

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.
- -(.- +

So I think this should be good to go. Can anyone please confirm. Thank you.

Should we document this somewhere on rhombus-tech.net?

3. Soldering iron ready:
I have my soldering iron ready. Richard, did you solder UART pins to the micro
desktop ([3])?

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 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? 


[1] http://lists.phcomp.co.uk/pipermail/arm-netbook/2019-July/016149.html
[2] http://lists.phcomp.co.uk/pipermail/arm-netbook/2019-July/016154.html
[3] http://lists.phcomp.co.uk/pipermail/arm-netbook/attachments/20190722/914a3283/attachment-0007.jpg
[4] http://rhombus-tech.net/allwinner/a20/boot/

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