ARM Announces 64-Bit Cortex-A50 Architecture

MojoKid writes "ARM debuted its new 64-bit microarchitecture today and announced the upcoming launch of a new set of Cortex processors, due in 2014. The two new chip architectures, dubbed the Cortex-A53 and Cortex-A57, are the most advanced CPUs the British company has ever built, and are integral to AMD's plans to drive dense server applications beginning in 2014. The new ARMv8 architecture adds 64-bit memory addressing, increases the number of general purpose registers to 30, and increases the size of the vector registers for NEON/SIMD operations. The Cortex-A57 and A-53 are both aimed at the mobile market. Partners that've already signed on to build ARMv8-based hardware include Samsung, AMD, Broadcom, Calxeda, and STMicro." The 64-bit ARM ISA is pretty interesting: it's more of wholesale overhaul than a set of additions to the 32-bit ISA.

Comments

A better article at anandtech.com

[IYagami]

Anandtech has a better article:

http://www.anandtech.com/show/6420/arms-cortex-a57-and-cortex-a53-the-first-64bit-armv8-cpu-cores

According to them, ARM Cortex A57 core is a tweaked ARM Cortex A15 core with 64 bit support. And ARM Cortex A53 core is a tweaked ARM Cortex A7 core with 64 bit support. It is possible to mix A57 and A53 cores in the same die to improve efficiency.

What I would like to see is this kind of approach in the x86 world. Imagine having an AMD processor with two fast cores (Piledriver's successor, Steamroller) for heavy processing and two lower cores for longer battery life (Bobcat's successor Jaguar).

Or Intel with their future Haswell and Silvermont architectures...

Re:ARM64 is a mess

[tlhIngan]

ARM 64's ISA is radically different than ARM32. All of the things that make Arm "ARM" are gone, such as conditional execution, having the program counter as general purpose register and more. Not only that, the binary encoding is totally different. The binary encoding for ARM64 is a total confusing mess compared to ARM32. I wouldn't say that ARM64 was a well designed ISA.

The binary encodings are a mess, yes, due mostly to the urge to adapt and produce some consistency with the AArch32 instructions. The ARM ABI has seriously evolved and the encoding possibilities are quite... nasty now if you look at ARMv7.

Thankfully, the assembler takes care of that for us.

Conditional execution is nice, but it really interferes with modern architectures. The ARMv8 core is a fully speculative, out-of-order with register renaming implementation. Conditional execution breaks this as the processor has to track more state since any combinations of instructions in the stream could have any combination of conditional execution.

Ditto the PC - it was nice to be able to jump by simply writing to the PC, but man does it complicate internal design if any instruction can arbitrarily move the PC to any register value. In the end, the few uses of conditional execution and the ability to move anything to the PC without using a branch or return style instruction was probably so limited, there was no point.

Oh, and there are 31 registers - X0 through X30. The 32nd register is special depending on the instruction - for ADD and SUB, "X31" means the stack pointer. For most other instructions, it means the zero register (reads as zero), something borrowed from MIPS, and allowing interesting register-only instruction forms to be used when the immediate value is zero. It does result in oddball uses though, like
      SUB SP, 0, X0 ; Set SP.
to play with the stack pointer.

If you're a system level programmer, AArch64 is MUCH nicer (no more damned coprocessors). I know, I've done a fair bit of it.