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Comment by 2bitencryption | Hacker News Reader

could someone explain how the Arm product pipeline works?

This is my (probably totally wrong) understanding:

Arm makes chip specification and defines assembly language --> companies (Samsung, Apple) license both of these and design their own chips following those specs --> these designs are sent to fabs and produced.

But what I don't get is, what "wiggle room" do companies like Apple and Samsung have to make their chips special? Obviously the M1 is a different beast from a Samsung chip, but they are both "Arm". So what is Apple able to do that makes the M1 the M1, while still also being "Armv8", the same "Armv8" as a Samsung chip? Does "Armv8" only mean "it must accept this instruction set, the rest is up to you"? Or is there requirements at the silicon level as well? Is this new Corex-A715 simply a "reference" chip for the next gen of the Arm instruction set?

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ARM produces both architecture specifications and the designs for chips that implement those specifications.

Some companies license the architecture specification and design their own implementations, Apple being the leading example. They then pay TSMC to fabricate the chips for them.

Other companies license the implementations and pay to have them fabricated. The latter category varies in the level of customization they apply to the implementations they license, it's generally much less customized than the what those in the first category achieve.

And Apple itself has a special architecture licensing relationship as one of the founding parties behind ARM Inc. Their $3MM investment ended up being a great deal for them. They can do whatever they want with the platform.

A lot of the customization is in the peripherals. ARM (AFAIK) really only specifies the processor, modern devices have lots of other on-board signals.

The instruction set really only defines how to run mathematical operations on the data on its bus, what to write to registers, and what instructions should load and store memory to various pages on the memory map.

Licensors add peripherals to do things that the instruction set doesn't define, like how to toggle an output pin from low to high. You use the instruction set to set a bit in a particular location in memory, and that turns on an LED attached to that pin - or they make a handy peripheral that lets you write to a word, because setting one bit in a 32-bit memory value is a read-modify-write 3-step operation and many of their devices have thousands of bytes of storage and RAM in an address space with billions of memory locations. They add I2C, SPI, CAN, Ethernet, USB, EEPROM, Flash, SRAM, video, etc. etc. etc. to make useful systems on chip - the processor is only one small part of that equation.

Good explanation from 2013 here:

https://www.anandtech.com/show/7112/the-arm-diaries-part-1-h...

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