Chapter 2. ARMv8-A Architecture and Processors

The ARM architecture dates back to 1985, but it has not stayed static. On the contrary, it has developed massively since the early ARM cores, adding features and capabilities at each step:

ARMv4 and earlier

These early processors used only the ARM 32-bit instruction set.

ARMv4T

The ARMv4T architecture added the Thumb 16-bit instruction set to the ARM 32-bit instruction set. This was the first widely licensed architecture. It was implemented by the ARM7TDMI® and ARM9TDMI® processors.

ARMv5TE

The ARMv5TE architecture added improvements for DSP-type operations, saturated arithmetic, and for ARM and Thumb interworking. The ARM926EJ-S® implements this architecture.

ARMv6

ARMv6 made several enhancements, including support for unaligned memory accesses, significant changes to the memory architecture and for multi-processor support. Additionally, some support for SIMD operations operating on bytes or halfwords within the 32-bit registers was included. The ARM1136JF-S® implements this architecture. The ARMv6 architecture also provided some optional extensions, notably Thumb-2 and Security Extensions (TrustZone®).Thumb-2 extends Thumb to be a mixed length 16-bit and 32-bit instruction set.

ARMv7-A

The ARMv7-A architecture makes the Thumb-2 extensions mandatory and adds the Advanced SIMD extensions (NEON). Before ARMv7, all cores conformed to essentially the same architecture or feature set. To help address an increasing range of differing applications, ARM introduced a set of architecture profiles:

  • ARMv7-A provides all the features necessary to support a platform Operating System such as Linux.

  • ARMv7-R provides predictable real-time high-performance.

  • ARMv7-M is targeted at deeply-embedded microcontrollers.

    An M profile was also added to the ARMv6 architecture to enable features for the older architecture. The ARMv6M profile is used by low-cost microprocessors with low power consumption.

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