AISgen

下面几个链接可以看看，说的比较明白。UBL= user boot loader，即二级boot。

Do I need a secondary bootloader (UBL)?

A secondary bootloader, AKA User Bootloader (UBL), was required on older devices, where the bootloader could not parse AIS files. By using the AISgen tool with the OMAP-L138 bootloader, most of the functions previously performed by the UBL can be done instead by the bootloader.

For a typical Linux application, the old flow looked something like this:

• UBL (sets up DDR, PSC, and copies U-Boot to memory)
• U-Boot (loads Linux and file system)
• Linux

The flow for the OMAP-L138 would look like this:

• AIS-signed U-boot (sets up DDR, PSC, and loads Linux and file system)
• Linux

So in general, there is not a need for a separate UBL, as the AIS functions can perform most of the same tasks.