mosfet is connected source to external 3.3V and drain to the board: as to be able to cut the power using gate signal (pulling gate high).
Based on your "hint" I powered up the board from laboratory power supply and set voltage 3.6V. Onion now works as expected. So definitely voltage drop across mosfet is more than 0.3V and that way, Onion Vdd get down to minimum allowed 2.97V causing an reset (and reboot: because voltage "recovers" to acceptable level).
Thanks for your help.
Since it is a flash chip we have added ourselves we will need to flash the OS onto it.
No. You must flash one of Omega2 Pro firmware onto the Omega2S+ onboard flash.
For example if you want to use the latest Omega2 Pro FW (2019-10-28) then flash it onto an Omega2S+:
sysupgrade -n --force omega2pro-v0.3.2-b232.bin
The full firmware upgrade process may take up to 5 minutes and your Omega2 Pro will reboot twice!
The first reboot will happen after the firmware has been updated, then once the device initializes, it will configure everything to run from the eMMC storage, after which it will reboot again. This will only happen on the first boot after an upgrade.
It'll take about 7 (seven!) minutes.
You should not press any key during this time - it is fully automatic.
You could watch the whole process on the Serial Console.
BTW The title of this article Booting from External Storage is a marketing bullshit.
An Omega2(+), Omega2S(+) or Omega2 Pro - with any present official Onion firmware - is not able to boot from any external storage (MicroSD card, USB memory storage or eMMC).
Please take a look at my project: DIY Omega2 Pro - Try it before buy
Unfortuntely I don't have any Omega2S+ and I can't solder any BGA chip - so I've made some experimental (or "fake" ;-) Omega2 Pro for myself.
Thanks everyone for the replies. I have been using the genuine Onion OLED. I found he issue, the connector seems to have an issue. If I jiggle it, it will start working, then stop working. I tested on 3 different OLEDs and I get the same behaviour so it's definitely my 2S+. I have more on order so hopefully I'll be ok once they arrive.
That command will completely disable Ethernet PHY, isn't it? It is the way, but I already use EPHY in my design, so no.
No, the ephy label in omega2-ctrl is misleading, it does not control ethernet phys, just the LED.
See AGPIO_CFG register for enabling/disabling ephys 1..4 (all together either ephy or GPIO, unfortunatly it is not possible to selectively enable only one of them -. ephy0 however can be used separately, with ephy1..4 in GPIO mode).
When I was designing a PCB for Omega 2S, I haven't had all the docs, and as a result I've used some of I2S pins, almost all SPI pins, etc. (literally, all the pins that could cause boot and other problems when they are pulled up/down) as a GPIO.
I was in the same situation a while ago when trying to find a usable wiring of my first Omega2 and Omega2S circuits, with all those various constraints...