For those who playing with RaspberryPi CM4 if you got it with eMMC storage onboard, please note that it's mounted to the same physical mount points as your SD card, so inserting SD card into IO board won't do anything. You actually have to use rpiboot to flash system onto eMMC directly. Here is official GitHub repo to use: https://github.com/raspberrypi/usbboot in case some one need it. #raspberrypi4