Hardware Altivec unit on the G4

[Guy Madison]

Years ago I figured out that there was a hardware programmable Altivec unit on the G4 series, it was integer only but it was definitely shipped on the G4 silver as it showed up IOReg. One of the hardware engineers at Apple verified my findings but didn't have any information on it other than it was like a DMA unit that allowed data to be processed directly in hardware vs the PPC processor.

Does anyone know about this ASIC or has it been lost to time?

 

[joevt]

Do you have the ioreg?

 

[paws]

Not sure what you're asking. Altivec is a set of extra "Single instruction, multiple data" aka SIMD or vector processing instructions in G4 PPC processors. It's not an ASIC, it's an ISA extension. There's no secrets at all, lots of PPC apps use it. You can start from https://en.wikipedia.org/wiki/AltiVec

 

[Guy Madison]

Your are correct Altivec is used in the G4, but Apple built a dedicated ASIC for media processing which was compatible with Altivec instructions.

I was just curious if there was any information out there on this ASIC.

 

[6a62]

as in a separate execution unit on chip, that handles AltiVec outside of the PPC core?

that sounds plausible, (Apple's AMX on their ARM chips works much the same) but I've never dug around in a G4. I'm very curious now!

 

[Guy Madison]

as in a separate execution unit on chip, that handles AltiVec outside of the PPC core?

that sounds plausible, (Apple's AMX on their ARM chips works much the same) but I've never dug around in a G4. I'm very curious now!

As a separate execution unit on a small ASIC on the motherboard. Its been a long time since I had a G4 silver, but I know its there.. I think it was called "Orca" with all the information floating around the web I was hoping to find something on this to hack with.

If you have a G4 silver check IOReg its may be in the memory controller or separate ... but its close to the CPU in the tree.

 

[paws]

Interesting! First I've heard of it, do update us if you find out more.