Talk:AArch64

cortex R82

I am not sure if the full v8a instruction set was implemented or just address space was extended to to 2TB(64bit)?

And need to add some product implementations ie. SSD/hdd models.
--:GSMC(Chief Mike) Kouklis U.S.NAVY Ret. ⛮🇺🇸 / 🇵🇭🌴^⍨talk 09:21, 10 May 2021 (UTC)

Why would it implement the v8-A version of A64, rather than the v8-R version of A64, given that it's a Cortex-R core?

And, according to the Arm Architecture Reference Manual Supplement - Armv8, for Armv8-R AArch64 architecture profile, section B1.1:

The Armv8-R AArch64 application level programmers’ model differs from the Armv8-A AArch64 profile in the following ways:

• Armv8-R AArch64 supports only a single Security state, Secure.
• EL2 is mandatory.
• EL3 is not supported.
• Armv8-R AArch64 supports the A64 ISA instruction set with some modifications.

The main changes appear to be some memory-barrier instruction changes. Guy Harris (talk) 20:21, 10 May 2021 (UTC)

What do "SSD" and "hdd" stand for? If they stand for "solid state drive" and "hard disk drive", presumably you're referring to disk drives using 64-bit Armv8-R processors as controllers. If that's the case, that might belong in pages about particular Arm cores used in those drives, rather than the AArch64 page. Guy Harris (talk) 20:24, 10 May 2021 (UTC)

About which term are you asking "just their terminology, or official"?

@Comp.arch: "conda-forge.org: "ARMv8 64-bit (formally known as `aarch64`)", just their terminology, or official?"

Presumably the intent was to ask that question here; edit comments unrelated to the edit are not the right way to ask questions about the article. Please ask them on the talk page, instead.

AArch64 is an official Arm term. As of 2022-01-10, the current edition of Arm® Architecture Reference Manual Armv8, for A-profile architecture says:

This manual describes the Arm® architecture v8, Armv8. The architecture describes the operation of an Armv8-A Processing element (PE), and this Manual includes descriptions of:

* The two Execution states, AArch64 and AArch32.

* The instruction sets:

— In AArch32 state, the A32 and T32 instruction sets, that are compatible with earlier versions of the Arm architecture.

— In AArch64 state, the A64 instruction set.

So:

We have the Arm Architecture, or the Arm CPU architecture.

It has multiple versions, including versions 7, 8, and 9.

Some of those versions have one or more profiles - the A-Profile, the R-Profile, and the M-Profile.

ARMv1 through ARMv5 have no profiles or execution states. According to the ARM Architecture Reference Manual ARMv7-A and ARMv7-R edition, ARMv4 had only the ARM instruction set, ARMv4T added Thumb, ARMv5T was the first v5 and included Thumb, ARMv6 included Thumb, and ARMv6T2 added Thumb-2.

ARMv7 introduced the profiles; an ARMv6-M profile, with Thumb only, was introduced either at that time or afterwards, but they didn't split the existing ARMv6 into ARMv6-A and ARMv6-R, as far as I can tell. ARMv7 was still 32-bit-only, with no execution states. ARMv7-A and ARMv7-R have both ARM and Thumb (including Thumb-2). ARM-v7M is Thumb-only (including Thumb-2).

Armv8 also has the profiles. It calls the ARM instruction set A32, the Thumb/Thumb-2 instruction set T32, and the new 64-bit instruction set A64. [Armv8-A introduced the execution states; I'm not sure whether a 32-bit-only or 64-bit-only implementation is allowed. Armv8-R also has AArch32 and AArch64. ARMv8-M supports only T32.

I presume this whole mess is due to 1) trying to support everything from the microcontroller market to the server and supercomputer markets, 2) allowing that broad customer base a choice of options for their application, and 3) the instruction set now having this all designed in from Day One so it has to get added on.

AArch64 is probably what "ARMv8 64-bit" could be called, although it's not unique to ARMv8 any more, as per the Arm® Architecture Reference Manual Supplement Armv9, for Armv9-A architecture profile, Issue A.a. As far as I can tell, "ARMv8 64-bit" is not an official Arm term (if nothing else, if it were, it'd be "Armv8 64bit" :-)). Guy Harris (talk) 02:49, 11 January 2022 (UTC)

And Arm's term for AArch64 and AArch32 is "Execution state" - a processor can be in AArch64 state, in which case it fetches and executes A64 instructions, or in AArch32 state, in which case it fetches and executes A32 or T32 instructions, depending on whether it's in "ARM" or "Thumb" mode (or whatever they call them now). The mode can change on an Exception level change, so trapping from a 32-bit application to a 64-bit OS kernel, or from a 32-bit OS to a 64-bit hypervisor, would switch from AArch32 to AArch64 on an EL0 -> EL1 or EL1 -> EL2 Exception level change, and returning from the latter to the former would switch from AArch64 to AArch32.

(I.e., it's not as if "AArch64" is an architecture with both 64-bit and 32-bit support. A processor with both 64-bit and 32-bit support can run in either AArch64 state or AArch32 state; a processor with only 64-bit support only supports AArch64 state and a processor with only 32-bit support only supports AArch32 state. I'm trying to find some documentation on whether either of those two are required by Armv8-A, or whether an Armv8-A processor is allowed to support only AArch64 or AArch32. Some hypothetical company that designs its own Armv8-A chips and develops its own operating systems could, if its Arm architecture license allows it, develop AArch64-only chips to run versions of its OSes that lack support for 32-bit applications, for example.) Guy Harris (talk) 09:02, 30 May 2024 (UTC)