Universal Payload
Universal Payload (UPL) is an Industry Standard for firmware components. UPL is designed to improve interoperability within the firmware industry, allowing mixing and matching of projects with less friction and fewer project-specific implementations. UPL is cross-platform, supporting ARM, x86 and RISC-V initially.
UPL is defined in termns of two firmware components:
- Platform Init
Perhaps initial setup of the hardware and jumps to the payload.
- Payload
Selects the OS to boot
In practice UPL can be used to handle any number of handoffs through the firmware startup process, with one program acting as platform init and another acting as the payload.
UPL provides a standard for three main pieces:
file format for the payload, which may comprise multiple images to load
handoff format for the information the payload needs, such as serial port, memory layout, etc.
machine state and register settings at the point of handoff
See also the upl command.
UPL in U-Boot
U-Boot supports:
writing a UPL handoff (devicetree) in SPL
reading a UPL handoff in U-Boot proper
creating a FIT
There are some new FIT features in UPL which are not yet supported in U-Boot.