The boot image in the emmc is used, even booting from sdcard?



I want to know what I exactly need to do for booting from the sdcard. According to the document at, in the section ‘3. Using a SD Card’, it mentioned that the ‘fastboot flash boot boot-fat.img’ command is needed for booting from the sdcard. This is confusing to me, because the sdcard should have the boot partition with boot image installed already, why flashing is still needed here. Furthermore, what is the target of this flashing operation? emmc or sdcard?



I just tried the debian snapshot build of 125. I burned it into sdcard and erase the emmc of my board with ‘fastboot erase …’. After insert the sdcard in and power on, the board can boot up, but the rootfs is mounted read-only.

Therefore, the flashing to emmc boot partition isn’t need here.