What is the SWIM PIC?

[olePigeon]

I was extracting chips off my battery bombed IIfx, and right next to the SWIM chip is the SWIM PIC. Any idea what it's for?

 

[Unknown_K]

The IIfx had a special serial controller chip to offload work from the 030 (only mac II to have it), could that be it?

 

[olePigeon]

I'll keep it bundled with my SWIM chip, then. I guess I was curious what was on it, and how it related to the SWIM chip. Like if the IIfx had an extra floppy shenanigans going on.

 

[olePigeon]

Also, my new cheapy-deapy hot air machine works fine. I broke it out yesterday to extract all the chips and a few of the black IIfx capacitors. I got the cheaper model after I returned the fancy (but still relatively cheap) model that didn't seem to ever get hot enough despite the temperature set to max and the airflow to low. I think it was broken.

 

[Unknown_K]

What models were they (hot air stations)?

 

[olePigeon]

I'll have to look when I get home. Just one of the generic Chinese models sold under 100 different names on Amazon and eBay.

 

[Gorgonops]

The "PIC" is more commonly known in the Apple docs as the "IOP"; the IIfx (and Quadra 900/950) have two of them programmed with different firmware; one sits in front of the serial ports and the other in front of the SWIM and the ADB ports. It's a custom MCU based on a 6502 core with a piddling amount of built-in RAM and a shared memory interface to the 68030, and it's intended to allow the main CPU to offload some of the hairier (and very timing-sensitive) aspects of handling disk I/O off so it can do other things.

Under plain MacOS these chips didn't accomplish much and were effectively kind of pointless, but the idea was sound and I vaguely recall reading that A/UX got at least some use out of them.

 

[olePigeon]

@Gorgonops So about as useful as A/ROSE.

 

[MOS8_030]

@Gorgonops So about as useful as A/ROSE.

That made me laugh!

From Wikipedia:
"A/ROSE is infamous for its esoteric purpose, which is generally not understood by Mac end users, as well as for causing many Mac emulators, such as Basilisk II, to produce a system error at boot time."

I think in all the years I've used Macs I only ran across one that actually needed the A/ROSE extension (network card) yet I saw it on hundreds of Macs because for years it was installed by default.

 

[NJRoadfan]

At least some of the design work saw practical use. Although it was built from discrete components, The Apple II 3.5" Controller Card uses a 65c02, a bit of RAM, and a SWIM to run floppy drives. The IOP is too system specific to use on an Apple II card though.

 

[Gorgonops]

The Lisa actually used a similar system to drive the floppy drives. Again, there's nothing really "wrong" with it in theory, it's a pretty big win in a multitasking system to not have to stall the main CPU so it can literally count cycles bit-banging disk I/O. It just didn't really pay off that much with the Mac System OS because it was by design not great at taking advantage of that sort of help.