ARM Trusted Firmware

Terminology

Source: [1]

EL0

Unprivileged (i.e. user space) runtime mode.

EL1

Standard OS (e.g. Linux) runtime mode.

EL3

"Secure world", trusted execution mode.

BL31

EL3 Runtime Firmware: AP_BL31

Also known as “SoC AP firmware” or “EL3 monitor firmware”. Its primary purpose is to handle transitions between the normal and secure world.

BL32

Secure-EL1 Payload (SP): AP_BL32

Typically this is a TEE or Trusted OS, providing runtime secure services to the normal world. However, it may refer to a more abstract Secure-EL1 Payload (SP).

External Links

• Official website [2]
• Official documentation [3]
  • Terminology [4]
• Official source code repository [5]
• Question on EL0/1/2/3 on ARMv8 [6]