1 the way to breed (https://breed.hackpascal.net/ )
baud is 57600. use minicom + usb ttl/serial converter.
/proc/mtd shows 0x30000 uboot + 0x10000 + 0x10000 layout, firmware start at 0x50000.
ralink sdk provides gpio commands to test button. in my case the button is gpio 12. this will be mapped to
gpios = <&gpio0 12 GPIO_ACTIVE_LOW>;
(so select 57600 baud, reset gpio 12 breed rom for mt7620a)
you need mtd command (unlock/erase/write/verify) to write to bootloader region. tftp to receive so/binary files and chmod +x.
LD_LIBRARY_PATH=/tmp /tmp/ld.so /tmp/mtd parameters
logging info shows there are some leds at gpio 10,11,40(unmodifiable to ethernet),14.
2 at breed
flash the initramfs-kernel version first. if booted, flash sysupgrade.
so it is important to find device dts/dtsi that could minimalize changes(baud, gpio keys, leds, rom layout). and optionally to disable sd/tf, usb if you dont have that.