OpenPOWER Firmware

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

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

Components

Firmware	Executed on	Loaded from	Function
SBE - OTPROM Source	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 - SEEPROM Source	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) Source	CPU core	SBE SEEPROM (on CPU)	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
Hostboot Source	CPU core	PNOR (SPI Flash)	initialises DRAM (memory training, zeroing of ECC memory, etc.), processor bus, memory buffers finally, chainloads Skiboot
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/Petitboot Source	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 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.
CME HCODE 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 HCODE Source	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 HCODE Source	IOPPE cores (on CPU)	PNOR (SPI Flash)	Involved in CAPI support.
OpenBMC Source	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

Process

1. SBE executes OTPROM, which loads SEEPROM firmware into SBE PIBMEM
2. SBE executes SEEPROM firmware
3. OpenBMC uses FSI interface to start SBE
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

• OpenBMC
• OpenPOWER

External Links

• OpenPOWER firmware source code on GitHub
• For a better understanding of OpenPOWER firmware and boot processes, see:
  • Overview of Boot Process
  • P9 Boot Flow
  • More OpenPOWER firmware documentation
  • OpenPOWER Firmware Stack - Joel's Weblog
• Bug tracker for firmware issues specific to Raptor CS products: https://bugs.raptorengineering.com/