Yokemate of Keyboards
Posts: 12526 from 2003/5/22
From: Germany
Addendum:
>> if the previous generations were, why change for the '060?
> I don't know, but I read that after the massively microcoded 68000,
> the following m68k generations used less and less microcode, so that
> the 68040 had relatively little microcode and the 68060 none at all.
A good decade later, confirmation from Motorola/Freescale/NXP's Joe Circello, lead designer of the 68060:
"
[...] machines like the 060 that don't have microcode [...]. [...] the 060 [...] was basically fully hardcoded, no microcode at all. [...] The 060, just to be clear, does not have any microcode per se in it. Everything is hardwired."
https://www.youtube.com/watch?v=1takr2k7Yfo (at 57:09, 1:03:48 and 1:17:12)
>> the '060's design really derives from the '060
>> (really a kind of super scalar version of the '40).
> There are significant opcode differences between the two. And as you said,
> it's a black box, so ISA design of the 060 may be derived from the 040's,
> but this isn't necessarily true for the microarchitectural design.
In the above-linked interview, Circello also confirms that the 060 microarchitecture is a from-scratch design started in 1988 (so during 030 era), i.e. not derived from any previous m68k microarchitecture. He furthermore tells the story how he and his team at his former company (Edge?) designed what would become the 060 unbeknown to Motorola and then knocked on Motorola's door to sell the (preliminary) design and team (and whole company?) to them, which Motorola agreed to. This means that Motorola didn't have any own plan to add an 040 successor (apart from trimmed-down ColdFire released for low-power customers in the same year as the 060), which would have ended the legacy with just that, and just took opportunity of the offer, which also explains why the 060 was released by Motorola after they had started selling PowerPC to their high-power customers, which is a thing many have been curious about.
Really interesting story I'd never heard or read about before.
