LWN: Comments on "Walleij: Setting up the Arm32 architecture"

Walleij: Setting up the Arm32 architecture

farnz — Thu, 05 Nov 2020 09:46:02 +0000

No, thank you for a great set of articles!

I just happened to know where to look for details of that vector, as I have vague memories of it from the Acorn Archimedes days. IIRC, ARMv4 can optionally run in ARM26 mode (at the discretion of the silicon designer), and ARMv5 onwards is ARM32 only. It's only ARMv1/ARMv2 that must run in ARM26 mode, and the last ARMv2 series chip was the ARM3.

ARM naming up until Cortex was confusing as all get-out, since the ARM610 is an ARMv3 chip, and the first ARMv5 chip is the ARM9 series, while ARM7, ARM8 and ARM9 chips are all ARMv4.

Walleij: Setting up the Arm32 architecture

linusw — Wed, 04 Nov 2020 22:18:10 +0000

Thanks! I updated the article with this information!

Walleij: Setting up the Arm32 architecture

farnz — Wed, 04 Nov 2020 09:26:10 +0000

For those people wondering (as I did) what the "address exception" vector that Linus refers to is, and why it's no longer in use; it's the vector ARM26 systems (ARMv1/ARMv2 architecture, ARM1/2/3 chips) used when a virtual address outside the 26 bit bus range was accessed. Because ARM32 systems have a 32 bit address bus and 32 bit address calculations (compared to ARM26 with 26 bit address bus and 32 bit address calculations), this vector is no longer needed.

Walleij: Setting up the Arm32 architecture

adam820 — Tue, 03 Nov 2020 22:49:03 +0000

Well, thanks for doing it; it helps out many others of us who are also trying to understand how it all works. :thumbsup:

Walleij: Setting up the Arm32 architecture

linusw — Tue, 03 Nov 2020 21:27:12 +0000

Of course I read LWN!
The series came about because I can't understand this volume of complex code unless I also explain it to others.

Walleij: Setting up the Arm32 architecture

pomac — Tue, 03 Nov 2020 16:00:03 +0000

I'll poke him if i see him :)

Walleij: Setting up the Arm32 architecture

lkundrak — Tue, 03 Nov 2020 12:29:41 +0000

This whole series is excellent.

Thank you Linus, if you're reading this.