Amlogic HDMI Boot Dongle

Schematics of the modified HDMI Display Emulator dongle : hdmi-amlogic-boot-dongle.pdf

The original emulator I bought at : https://s.click.aliexpress.com/e/bnNfDBb6 I only changed the A1 pin from GND to VCC

The amlogic BootROM reads 8bytes at the EEPROM address 0x52, offset 0xf8 (248). If the 8bytes content is boot@USB it will force USB boot mode. You should be able force SDCard with boot@SDC (not tested). To flash the EEPROM, simply connect the dongle to the HDMI port while linux is running, and add a new i2c device on the hdmi i2c port :

cd /sys/class/i2c-dev/i2c-0
echo 24c02 0x52 > new_device
cd *-0052
echo -n "boot@USB" | dd of=eeprom bs=1 seek=248 count=8
dd if=eeprom bs=1 skip=248 | hexdump

in my tests, the last byte was not flashed correctly... so I did:

echo -n "B" | dd of=eeprom bs=1 seek=255 count=1