Try enabling the debug UART by setting BOOT_UART in the bootcode EEPROM? Details at https://www.raspberrypi.org/documentation/hardware/raspberrypi/booteeprom.md You'll need a USB to 3.3V UART adapter or cable. Thanks for the advice! I happen to have a USB to 3.3V UART adapter on hand so I tried it,...

I ask this question because I have an eMMC module that can work as bootable micro SD card on my Pi 3B and 3B+, but it is not recognised by Pi 4. I have flashed the latest Raspbian on this eMMC module, and it can boot my Pi 3, but not Pi 4, while a micro SD card with the same Raspbian can boot my Pi ...

I have an eMMC->micro SD adapter, which allows me to use a 16GB eMMC chip as the storage for Raspberry Pi, via the SD card interface. It worked perfectly on all Raspberry Pi models, and it indeed has much higher speed on 4k writing than any micro SD card I can find. https://i.ibb.co/brBb8M1/1.jpg Un...