U-Boot

Linux friendly bootloader. Used in various ARM devices like PinePhone and Orange Pi.

Boot process

• SPL (Secondary Program Loader) is a small binary, generated from U-Boot source, that fits in the SRAM and loads the main U-Boot into system RAM.[1]
• TPL (Tertiary Program Loader) Tiny SPL loads moderate-size middle layer called TPL

Related

• U-Boot on Allwinner devices
• U-Boot on Orange Pi 4

External

• Presentation of U-Boot and porting to devices [2]
• Get More out of U-Boot (introduction, partitioning, etc.) [3]
• Presentation on TPL: SPL loading SPL (and what is SPL?) [4]