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Posted Wed Jan 15, 2020 4:34 am

Wondering if any one knows what the difference is between the 2 revisions of buster on the A2000?



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Seattle, WA, USA

Posted Wed Jan 15, 2020 11:16 am

There is some detailed information about the Buster at The Big Book of Amiga Hardware. Dave Haynie dropped a ton of information about Buster over there.

According to Dave Haynie:
Though you think it's the same chip, there are actually two Busters: Level I and Level II. The Level I Buster, up to Rev 7, is used in all A3000 family machines, and it does NOT support Zorro III bus masters. Doesn't even try.

There came a time in the A3000 development where I had to chose between adding more Zorro III features (I designed the whole bus specification before I did the chip work) and getting Zorro II compatibility up to par. Zorro II was tricky -- in essence, it's a 68000 bus emulator in there, and some of the interactions between 68K procotol and real Zorro II hardware were not things you could have easily predicted at the start of the project. And given that C= management hadn't even asked for expansion bus improvements on the A3000 (all my idea), you can see where Level I came from.

The Level II part (about twice as many gates) was out in two revisions; Rev 9, which initially shipped with the A4000, and Rev 11, which is the best you'll ever get. The Rev 9 part has two bugs that can cause problems with Zorro III cards. One can affect some kinds of bus slave cards, it depends on the card design. This is due to a small flaw in a synchronizer stage in the Level II chip (Level II runs a slightly faster bus protocol than Level I, and also supports burst). The other is a flaw in the Zorro III bus arbiter -- there's a small window in which a Zorro III slave cycle just starting can confuse a bus registration command, locking the bus.

Rev 11 solves both problems, so you need it for DMA devices. The Rev 9 problems were fairly well qualified, so you have some devices that offered work-arounds. I didn't for the A4091 -- at the time, C= probably wouldn't have let me do the Rev 11 chip if the A4091 could have worked at all in existing A4000s. A3000s use the Level I Buster, never intended to work with something like the A4091. The Rev 11 part works fine in the A3000, and in fact fixed a race condition between Gary and the chip bus that can cause memory failured during Zorro II DMA to Chip RAM. The big problem with Buster testing was the lack of any Zorro III cards to test it with. Very early on, I did a memory card, which tested normal slave access and even supported burst, though I didn't have a Buster that did for a year after this.

The next test board was done for the multiprocessor project. This "Gemini" board tested the remaining Level II features: bus arbitration, bus mastering, Quick Interrupts, etc. Unfortunately, I based it on the Buster chip (there's a secret mode in Buster Level II that lets it run as a card controller rather than a motherboard controller). But that year (1991), CSG was changing over from channelled gate arrays to sea-of-gates technology, and their first chips were running at 1/4 speed or so.

Six months later, I had fast chips, but also the new Engineering Administration, which considered Gemini either an illegal research project, or "something from the last administration". So no big pounding on the Zorro III bus was possible before the A4000 shipped. In all fairness, the Zorro III project was a large thing to bite off. When The PC Industry made EISA, there were hundreds of people involved: some to hammer out the specs, some to make chips, test, etc. At Commodore, it was basically just me for most of the life of Zorro III. The A4091 doesn't work with Level I Buster. Also, if you have an older A4091, OS2.04 or SuperKickStart could prevent it from booting, it would require 3.0 or 3.1 ROMs. And, just as a technical detail, Zorro III doesn't use a clock. The Z3 timing is based on your motherboard clock, but the bus protocol itself is asynchronous.

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New Orleans, LA, USA

Posted Wed Jan 15, 2020 1:01 pm

Yes, but, the Buster in the 2000 is completely's even a different silicon package, DIP vs PLCC, with far fewer pins. Most of that info from Dave Haynie seems to be referring to PLCC variants.

OP, sorry I can't contribute much to answer your question. I wasn't able to locate this information myself during my A2000 replica build.

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Posted Wed Jan 15, 2020 3:55 pm

Thanks Guys

Had a look on BBOAH but yeah its related to the A3000/4000 ones.. I am guessing that since there is no info on the difference it doesn't make much of a difference then. :-D

I am about to do a build of a A2000 board myself, so I need to acquire a buster as I will be using most of the components from a A500.

Thanks for the replies!

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Posted Thu Jan 16, 2020 6:48 am

I took the same route. I ended up buying a Buster chip from eBay. I hope that you are able to do the same.

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Posted Sun Jan 19, 2020 12:33 am

You need the -02 Buster. The -01 Buster has a significant bug which prevents Zorro DMA to work. The -01 Buster is very rare and was really only used with the Rev 3.9 A2000B motherboard where it was placed on a separate PCB called Buster Tower. This PCB also had a PAL chip to correct the bug.
I have seen 2 A2000 -01 Busters. One on my Rev 3.9 motherboard, the other on a friend's Rev 3.9 motherboard.

The same issue occured (and was the cause due to copied logic equations) with the A2000A. There a PAL had a wrong equation and switched the data bus buffers the wrong way during Zorro DMA. Commodore provided a replacement PAL with the A2090 controllers.

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Posted Sun Jan 19, 2020 3:12 am

Interesting stuff. I had no idea that there was more than one revision of the A2000 Buster.

One thing that may be useful information for you, Nadoom is that I believe the A2000 will boot okay without the Buster chip being present. So there is no reason to delay your testing if your search for a Buster chip is prolonged. I have also heard that you can even use a single Zorro card without the Buster chip being present. I have never tested this though.

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Posted Mon Jan 20, 2020 3:18 pm

@Christian Thanks for the insight on the issues with the 01 revision. Good to know when I am looking around for one.

@grshaw thanks for the heads up on that, I will get one eventually as i have a GVP zorro card laying around here some where, but it means like you said I can get it up and running quicker and don't have to rush it.

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