OpenPOWER Firmware

From RCS Wiki
Jump to navigation Jump to search

OpenPOWER Firmware is an open-source alternative to OpenFirmware and proprietary IBM firmware used on Power machines.[1] It is a general name for many separate pieces of software used to start recent Power Architecture chips made by IBM.[2]

OpenBMC is a separate project that creates firmware for the Baseboard Management Controller.


Firmware Executed on Loaded from Function


SBE core (on CPU) OTPROM (on CPU die) The portion of Self-Boot Engine (SBE) firmware permanently written via eFuses into the POWER9 silicon's OTPROM
  • very first instructions executed
  • loads remaining SBE firmware from SEEPROM into SBE core


SBE core (on CPU) SBE SEEPROM (on CPU) The portion of Self-Boot Engine (SBE) firmware run from rewritable SEEPROM
  • initialises CPU core
  • loads Hostboot Bootloader
  • backup copy stored on PNOR SPI Flash, used to stage SBE firmware updates
Hostboot Bootloader (HBBL)


  • first code which runs on main CPU cores; loads and executes rest of Hostboot
  • responsible for verifying integrity of Hostboot when secure boot is enabled, so this part of Hostboot is stored on the SBE SEEPROM, even though its source code lives inside the Hostboot repository

Raptor Source Upstream Source

CPU core PNOR (SPI Flash)
  • initialises DRAM (memory training, zeroing of ECC memory, etc.), processor bus, memory buffers
  • finally, chainloads Skiboot

Raptor Source Upstream Source

CPU core PNOR (SPI Flash)
  • initialises PCIe controllers, device trees, real time clock, NVlink, sensors
  • loads OCC firmware and starts OCC running
  • implements OpenPOWER Abstraction Layer (OPAL) for OS runtime services; remains resident in RAM after OS boot
  • finally, chainloads Skiroot

Skiroot Linux Config Source (Talos II)
Skiroot Linux Config Source (Blackbird)
Petitboot Source
Skiroot Linux Config GitLab (Talos II)
Skiroot Linux Config GitLab (Blackbird)

CPU core PNOR (SPI Flash)
  • Skiroot refers to the Linux kernel and initramfs which runs from RAM
  • Contains Petitboot, a userspace application which provides a boot menu
  • Petitboot loads operating system via kexec
OCC firmware

Raptor Source Upstream Source

OCC core (on CPU) PNOR (SPI Flash) The On-Chip Controller (OCC) manages:
  • thermal regulation of CPU chip, turbo frequency selection, voltage ID selection, power measurement, etc.

Raptor Source Upstream Source

CME cores (on CPU) PNOR (SPI Flash) The Core Management Engines (CME) are auxillary cores used for power management purposes. They are ultimately responsible to the OCC.
  • There is one CME for every pair of SMT4 cores.


SGPE and PGPE cores (on CPU) PNOR (SPI Flash) General Purpose Engine (GPE) cores which assist, and are managed by, the OCC.
  • The Stop GPEs (SGPEs) are part of the mechanism for resuming execution after a STOP instruction is executed (which is a Power ISA instruction which halts the processor).
  • The Pstate GPEs (PGPEs) perform pstate management.


IOPPE cores (on CPU) PNOR (SPI Flash)
  • Involved in CAPI support.


BMC chip BMC SPI Flash

(This is not part of OpenPOWER firmware, but is mentioned to give a picture of the division of responsibilities. Not all POWER9 systems use a BMC; IBM systems use a FSP.)

  • Turns system power rails on and off to energise and deenergise CPU modules, RAM, etc.
  • Sends commands to CPU modules over FSI to commence booting.
  • Provides access to PNOR SPI flash containing host firmware via LPC.
  • Receives core temperature information from the OCC; decides and sets fan speeds.
  • Powers off system if OCC indicates catastrophic temperature.
Diagram of main and auxillary cores on POWER9


  1. OpenBMC uses FSI interface to start SBE
  2. SBE executes OTPROM, which loads SEEPROM firmware into SBE PIBMEM
  3. SBE executes SEEPROM firmware
  4. SBE loads Hostboot
  5. Hostboot loads Skiboot
  6. Skiboot loads OCC, Skiroot
  7. Petitboot application within Skiroot loads the operating system
  8. OS talks to firmware through OPAL


See also

External Links