ARM ISA

General

History Families

Variants

26-bit 32-bit 64-bit

Extensions

ARM Thumb ThumbEE Jazelle VFP Neon Helium

Topics

Addressing Modes Registers Assembly Interrupts CPSR Modes Calling Convention Microarchitectures

Versions(all)

ARMv1 ARMv2 ARMv2a ARMv3 ARMv4 ARMv5 ARMv6 ARMv7 ARMv8 ARMv8.1 ARMv8.2 ARMv8.3

ARMv8.1 is an extension to ARMv8, an ARM instruction set architecture which brought a large number of fundamental changes to the instruction set, including the introduction of 64-bit operating capabilities.

Mandatory Features from ARMv8.0

• CRC32 was optional in ARMv8.0, now mandatory.

Mandatory Features in ARMv8.1

• Large System Extensions (LSE)
  • New atomic instructions to support scalable performance:
  • Instructions for full-word, half-word, and byte operations are available.
  • Most of the following have optional load-acquire and/or store-release semantics.
    • Compare and Swap: CAS, CASP (up to 128-bit values).
    • Atomic Memory Operations: ADD, CLR, EOR, SET, MAX (signed/unsigned), MIN (signed/unsigned).
      • LD<op> versions return the value of the updated memory (LDADD for example).
      • ST<op> versions are "fire-and-forget" (STADD for example).
    • SWAP
• Rounding Double Multiply Add/Subtract instruction (RDMA)
• Limited Ordering Regions (LOR)
• Privileged access never (PAN)
• Virtualization Host Extensions (VHE)

Optional Features in ARMv8.1

• Hierarchical permission disables (HPD)
• 16-bit VMID (VMID16)
• PMU Extensions (PMU)