For bootstrap mode, it refers to the communcation between the host and ROM codes through serial download protocol. The purpose of this mode is to download MFGTool firmwares (Uboot/kernel/rootfs) to the devices and then jump to the Uboot of MFGTool firmwares. The VID and PID are aligned with ROM codes.
Updater mode, it refers to the communcation between the host and MFGTool firmware through UTP defined in kernel. So its VID and PID are different.
In the "BootStrap" part, it will load the firmware (u-boot, kernel and RAM filesystem) to the DDR.Then the board will boot up and running the firmware, it is a small linux system.
When the system is up, the storage device will be under the /dev/. For example, the device of SD Card is mmcblk.Then in the "Updater" part, it can use the linux commands to download the images to the SD Card.