68040 and FPU mania

[zefrenchtoon]

I've absolutely no idea how anyone was ever meant to do anything useful with it.

 

[zefrenchtoon]

Maybe an easier way to update the ROM (I mean without splitting it to flash 2 CI instead of 1 if I'm not wrong)

 

[Paralel]

Very interesting! Thanks for the information! Question, would the classic II really benefit from running the fpu at 40Mhz given that the bus is only 16bits wide?

The card also looks very cloneable . Might be a project for later

Surprisingly, it does improve the performance by more than 20%. Given the difference in the speed between 16 and 40 MHz, I think it likely maxes out what is possible with the Classic II's limited bus. I know I have some benchmarks around here with the 40 MHz and it handily beats the SE/30 with synchronous FPU.

Maybe it allows you to put a bigger one than the stock one ? (I'm a newbie in this domain, this can be completly wtf what I said) ^^'

Yeah, it gives you access to 3 MB of ROM space above the 1 MB reserved for the System ROM (if you have the jumper in that position). Unfortunately it seems to be a mostly unimplemented feature, something they were apparently working on that they dropped and they just didn't bother to remove from the design. I haven't been able to come up with much use for it other than as a ROM disk accessible after booting.

You can't boot from it since the driver to do so is missing from the System ROM (that would have been the killer application). I think it was BBraun that was able to alter the system ROM so the expanded ROM can be booted from, of course, that requires installing a re-written System ROM, which is more than most want to do to access an expanded ROM space.

With the ROM expansion in place and the logic board set to "1/3" you can access the 3 MB ROM space of the expansion as a ROM disk with an extension that was also written by BBraun. Given the speed of ROM disk (even constrained by the bus), it could be useful for something, but its applications are still rather limited.

The ROM expansion also makes the card much more expensive to make. With just an FPU you can do a 2 layer PCB. With the ROM you need a 4 layer PCB. Back then I can imagine the difference was that much greater.

 

[zefrenchtoon]

Surprisingly, it does improve the performance by more than 20%. Given the difference in the speed between 16 and 40 MHz, I think it likely maxes out what is possible with the Classic II's limited bus. I know I have some benchmarks around here with the 40 MHz and it handily beats the SE/30 with synchronous FPU.

There are some benchmarks here:
https://68kmla.org/bb/index.php?thr...classic-ii-and-performa-200.39312/post-439486