Zorro 3 Bus Speed

[Zac67]

I remember that somebody made his A4000 a lot faster by downgrading the crystal of the motherboard to something like 27 Mhz or so and that did speed up the fps of Quake a lot, though normal motherboard things screwed up so he could only use this trick when using the gfx card and soundcard ....

... probably just slowed down the stopwatch for measuring the fps... The 28 MHz clock drives the chipset and the CIAs housing the system timers. If the CPU clock doesn't change (like it wouldn't in a 4000) it appears to run faster because of the time warp.

I'd overclocked my A500 back in '89 with a 32 MHz crystal. It did work nicely but my RGB monitor was literally screaming from the increased scan rate - and the integrated clock was running quite fast.

[Zac67]

Zorro3 can be overclocked to 33Mhz too but real amiga video and sound will probably suffer.

Hmm - Zorro III doesn't actually have a clock, it's all asynchronous...

[Zac67]

So it seems perfectly possible to install a jumper that allows you to run the 33 Mhz once the drivers for gfx card and sound card are loaded so the standard video and sound won't be used anymore ?! I thought the way to do this was to use a slower crystal and not faster ...

How's overclocking the chipset supposed to have any impact on Zorro III operations? Zorro II might be another story since its clock is derived from the 28 MHz clock, but Z3 is much faster anyway.

And how does a slower crystal speed up things???

[Zac67]

I mean overclocking the entire motherboard. Perhaps just the buster part could be overclocked, I don't know. My friend Frank Brana overclocked his A2000 denise (and fried a pair of them) and got 31Khz video (but he told me demos didn't look good)

Buster runs off the CPU clock, so raising that would overclock the CPU section and Buster. The chipset section has its own (28 MHz) clock and runs asynchronously.

Overclocking will speed up things (like CPU, bus, ...) while getting you closer to the edge. Once you've exhausted the tolerances in your system and exceeded the inherent speed limit you're outa luck and crash the system. On the 3000 the probable first point of failure is the SCSI adapter - don't try with your 'good' drive.

Depending on whether the Z3 bus is the bottleneck for a given operation and how the PIC copes with the higher speed, your system might get faster - or not.

IMHO, a much better approach to speeding up the system is to look at current limits. E.g. I've been told that you can significantly speed up motherboard fast RAM by using 50 ns or 'very good' 60 ns RAMs and setting Ramsey to 16 MHz mode, thus bypassing a wait state. Probably this would also speed up Z3 DMA and PIO operations.

[Zac67]

Hmm...

Actually lowering a clock speed can't speed up anything (apart from the rare occasion where you profit from a quicker sync on asynchronous bus operations).
The only thing speeding up might be perceived speed in the case of slowing the stopwatch while not changing the speed of the actually gauged hardware. That would be the case if you underclock the chipset while keeping the same CPU speed.

[Zac67]

Before actually re-inventing Super Buster it's probably a more promising approach to leave out Zorro III altogether (sorry Dave) and directly interface to PCI/PCIe with an appropriate new daughterboard, ideally 1x video, 2x Z3/PCIe shared, 1x Z3/PCI shared.

If you also include a faster-than-motherboard (which is an '030 bus), direct PCI(e) interface for future accelerator cards, you've completely circumvented the ancient bottlenecks. Just add a somewhat modern 1 Gig graphics card for RAM and you're set. Anyone?

[Zac67]

Exactly - but that's limited to that single video card. Adding a modern gfx card plus maybe a fast SCSI or SATA adapter and a GE NIC would be so much nicer, wouldn't it? Btw, I'd include USB, SATA, and Ethernet right on the daughterboard - while we're at it...

[Zac67]

im not sure if the cards would be able to take advantage of updated speed.

No, not at all. Probably it'd be wise to stick at the current speed for compatibility reasons.

My intention in talking about PCI/e was that once you pick up this task you should do the job thoroughly - without adding too much complexity, PCI soft cores are around.

Step 1: You could redo the Buster, maybe speeding it up a bit, but most of all removing the bugs.

Step 2: Integrating a PCI port opens the door for replacing the daughterboard with one carrying any mix of Z3, PCI or PCIe slots, connected to the Buster PCB by a ribbon cable. Better PCI performance without messing with Z3.

Step 3: The daughterboard has yet another connector for hooking up an accelerator board directly to the PCI world. Except for the Bvision port danbeaver mentioned all other solutions require the - fast - accelerator to go over the - slow - motherboard bus to reach a - fast - PCI busboard. Obvious where the bottleneck sits.
At the same time the '030-to-PCI bridge we built into Buster starts to work the other way around, interfacing the accelerator to the motherboard, removing some complexity from accelerator design.

Step 4: Why use an expensive and hard-to-get 68060 CPU? Better take a cheap, fast and cool(!) ARM CPU with integrated PCIe and 68k emulation in firmware. You won't see a difference except that it's faster. The 5V adaption problem has already been solved with the Buster replacement.

[Zac67]

WTF? 150 MB/sec Zorro3! Wiki is full of BS!

The 150 MB/s (burst) figure comes directly from Dave Haynie. It assumes a 'perfect' implementation which Super Buster is far from.

Getting to or somewhere near this speed in any present Amiga won't be possible. The '030 bus of the motherboard and the memory bottleneck will definitely prevent it from reaching anything far beyond 20 MB/s. Many existing Z3 cards may also become problematic when raising the bus speed significantly. You can't even blame the developers - there simply is no platform to test them against.