EOMA68-A20 2.7.4 preproduction board

http://lists.phcomp.co.uk/pipermail/arm-netbook/2020-June/016289.html

This is a work in progress. Following how-to can be wrong, incomplete or broken. This could result in damaged hardware and data-loss. In its current state it is not (yet) vetted and tested by the project founder and the arm-netbook community. Please seek advice first and ask questions on the arm-netbook mailing list (http://lists.phcomp.co.uk/mailman/listinfo/arm-netbook).

Hardware

Connect board with 1.7 Micro Desktop

  • Add links to messages in mailing list archives
  • Link to pictures and add Lukes comments underneath

Solder UART connection to 1.7 Micro Desktop

  • solder UART pins (2.54 mm pitch, it's designed precisely for that.)
    • Add links to messages in mailing list archives
    • Link to picture (http://rhombus-tech.net/allwinner/a20/eoma68_a20_usb_uart_connect.jpg)
      • there you will see only GND, TX and RX connected. do not under any circumstances connect the VCC_IO line. this is a reference power supply from the USB UART. so is the 3.3v supply from the EOMA68 PCB. if you connect them together they will destroy each other.

http://rhombus-tech.net/allwinner/a20/micro_desktop_usbuart/

DC Power Supply Unit for Micro Desktop

http://rhombus-tech.net/allwinner/a20/micro_desktop_usbuart/

  • Todo; summary of mails

Anti-static advice

also, once inserted, place the anti-static bag in between the Card and the MicroDesktop PCB. it's there to protect against possible short-circuit. the top of the MD is lacquered, and there are no components, however why take the risk? just slide it in gently in a U-shape.

Given that USB UART is "pulldown" (floating indicates LOW) it is perfectly fine not to have a converter IC. when doing it this way (without a converter IC) you will find however that even just the power coming from the TX and RX pins is enough to provide 3.3v to the actual A20 processor. therefore you will need to disconnect the USB cable when powering down. simply switching off the 12v PSU (15v in your case) is not enough.

also watch out for GROUND loops between:

  • laptop / desktop PSU
    • laptop / desktop
    • USB UART port connected to laptop
    • EOMA68 PCB
    • 12 (15) volt PSU

if you get problems (which will show up as corrupted data and possible eventual destruction of the FT232 USB UART IC - yes this is just how it goes) then disconnect the laptop's PSU whilst powering on.

http://lists.phcomp.co.uk/pipermail/arm-netbook/2020-July/016302.html

Software

U-Boot

Sunxi U-Boot (legacy)

https://linux-sunxi.org/U-Boot/Legacy_U-Boot

gcc-4.9 (Debian) works. gcc-6 and gcc-8 do not build. Probably related to https://github.com/linux-sunxi/sunxi-bsp/issues/16

see Building U-Boot, Buildroot Toolchain and boot

git checkout v2013.07-sunxi.4

if desired create branch

git checkout -b v2013.07-sunxi.4_foobar

see http://git.rhombus-tech.net/?p=u-boot.git;a=shortlog;h=refs/heads/sunxi change EOMA68_A20 section in boards.cfg. With sunxi U-Boot v2013.07-sunxi.4 special _FEL sections seem no longer necessary as a u-boot-sunxi-with-spl.bin is created that one can boot with

sunxi-fel uboot u-boot-sunxi-with-spl.bin

To write sunxi U-Boot to SD-Card see https://linux-sunxi.org/Bootable_SD_card#Bootloader (commands described after v2013.07 or earlier seem to work)

Boot via FEL

connect UART, eject all µSD-cards, hold '2' on keyboard while applying power to Micro-Desktop, hold '2' for a while, connect µUSB-cable to computer card, make sure board is in FEL-mode with

sunxi-fel version

Boot sunxi U-Boot via FEL from U-Boot folder:

sunxi-fel write 0x2000 ./spl/u-boot-spl.bin
sunxi-fel exe 0x2000
sunxi-fel write 0x4a000000 ./u-boot.bin
sunxi-fel exe 0x4a000000

or with sunxi U-Boot v2013.07-sunxi.4

sunxi-fel uboot u-boot-sunxi-with-spl.bin

To be tested (means to check two MMC slots in the early SPL loader):

Mainline U-Boot

Kernel

https://www.crowdsupply.com/eoma68/micro-desktop/updates/274-eoma68-a20-cards-arrived

The linux-sunxi-3.4.104 kernel on the other hand has bugs in it (which are different from the bugs in the mainline sunxi linux kernel). Basically the symptoms are: if you boot from SDC0 (on the Micro Desktop housing) and then put a microSD card into SDC2 (on the EOMA68-A20 Card) all is well. If however booting is carried out from SDC2 followed by inserting a Card into SDC0, SDC0 is guaranteed to get a "read error". This is annoying… and I am not going to fix it: I just don’t have time. If anyone would like to submit a patch or knows of a fix…. or is prepared to make a bug report (using the proprietary services that the sunxi community utilise) you are most welcome to do so: you would be helping out 800 other people in the process.

sunxi 3.4: https://linux-sunxi.org/Linux_Kernel

SD-Card

https://linux-sunxi.org/Bootable_SD_card

but

sudo mkfs.ext4 /dev/sdX2 -O ^metadata_csum

to prevent kernel error while mounting rootfs.

rootfs

debootstrap Debian Stretch (https://linux-sunxi.org/Debootstrap), Buster -> sunxi 3.4 kernel freeze

https://www.mail-archive.com/debian-user@lists.debian.org/msg758201.html

Notes