Server Base System Architecture

The Server Base System Architecture (SBSA) is a hardware system architecture for servers based on 64-bit ARM processors.^[1][2][3][4]

Historically, ARM-based products have often been tailored for specific applications and power profiles. Variation between ARM-based hardware platforms has been an impediment requiring operating system adjustments for each product.

The SBSA seeks to strengthen the ARM ecosystem by specifying a minimal set of standardized features so that an OS built for this standard platform should function correctly without modification on all hardware products compliant with the specification.

• CPU features
• Memory management
• Peripheral access
• Interrupts
• Watchdog (errant system detection)

Existing specifications for USB, PCIe, ACPI, TPM, and other standards are incorporated to solidify the specification.

Firmware issues are addressed separately in the Server Base Boot Requirements (SBBR) specification.^[5]

The Architecture Compliance Suite (ACS) checks whether an environment is compliant with the SBSA specification, and is provided under an Apache 2 open source license. It is available at https://github.com/ARM-software/sbsa-acs.

The specification defines levels of compliance, with level 0 being the most basic, and successive levels building on prior levels. In the words of the spec, "Unless explicitly stated, all specification items belonging to level N apply to levels greater than N."

Levels 0, 1, and 2 have been deprecated and folded into level 3.

Level 3 contains base-level specifications for:

• PE (Processing Element--a core) features
• Memory map
• Interrupt controller
• PPI (peripheral interrupt) assignments
• MMU behavior
• Clock and timer subsystem
• Wake up semantics
• Power state semantics
• Watchdogs
• Peripheral subsystems

Extends level 3, e.g. with support for RAS fault recovery extensions of ARMv8.2 spec.

Extends level 4, e.g. with support for stage 2 translation control from hypervisor as specified in ARMv8.4.

Extends level 5, e.g. with support for speculative execution safety features.

Extends level 6, e.g. with support for Arm Memory System Resource Partitioning and Monitoring (MPAM) and Performance Monitoring Unit (PMU) features.

Initial public version of the SBSA was announced on January 29, 2014.

SBSA Version 3.0 was released on February 1, 2016.

SBSA Version 5.0 was released on May 30, 2018.

SBSA Version 6.0 was released on September 16, 2019.

SBSA Version 6.1 was released on September 15, 2020.

SBSA Version 7.0 was released on January 31, 2021.

SBSA Version 7.1 was released on October 6, 2022.

• UEFI
• ACPI

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