Original poster is right. looks like a bug in the boot ROM. It wants 120,000 baud rate, not 115200.
Context: Omega2+ in mini-dock, Win10 64 bit, trashed file system, want to go back to factory firmware. Wifi connectivity also trashed.
Holding the reset button down for 10 seconds does not work, still trying to boot from the micro SD card
So I wanted to update the firmware from a USB stick, following the procedure in the documentation.
I inserted the USB stick.
Holding down the reset button while turning power on, the serial port disconnects soon after power-up. Only way to recover is disconnect and reconnect USB, but this forces a power cycle. No good in the mini-dock.
Tried the same process in a Linux system, silent failure this time but still no luck.
Move to a Power Dock 2, soldered on a SparkFun Serial Basic card (CH340). Made sure it was jumpered for 3.3V! Pins 1 gnd 5 Tx 6 Rx (seen from serial card end) .
Note - you can't do this with a mini-dock etc. because your external serial card will be fighting with the internal serial converter chip.
Now it comes on with reset button held, but screen full of trash for 40 seconds then a normal boot.
Then I came across this comment, inspiring me to try 120000 baud rate instead of 115,200. Works!
Procedure - set PuTTY for 120,000, power on holding reset button until fast blink, zip over to the keyboard and hit 2 quick as a bunny, system loads from USB stick and then does normal boot. Switch PuTTY back to 115200, hit enter and the prompt shows up.
Don't know why it skips the log-in or why it needs a carriage return. But that has been my experience with this system using the hardware serial port.
There seems to be no other way to unbrick a non-WiFi capable Omega2, except maybe if you have an Ethernet dock. Probably same problem trying to use a micro-SD card.