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From: Eric Smith on 19 May 2006 03:53 Michael J. Mahon wrote: > The fact that both companies used "custom" 6502 processors for their > machines is no doubt part of the reason that they never moved forward. John Selck <selck_j(a)informatik.hgv-hamburg.de> writes: > Huh? They did move forward. 6510 -> 8500 -> 8502. That was a progression of nearly insignificant changes. Not comparable to e.g. the 8086/80286/80386 progression, or even to the 6502/65C02/65816 progression. > And also, I don't > think it's any kind of problem for Commodore to use customized CPUs > since they owned MOS, the owners and producers of 6502 tech back then Yes, it was a problem for them. Designing (or even just modifying) a processor costs a lot of money, even if you own the fab. You don't do it unless you have a business plan with a reasonable expectation of (more than) recouping those costs. In a modern process, a production mask set costs about $0.5-$1 million if you don't own the fab, maybe 20% of that if you do. Back in the 1980s with larger process geometries the costs were lower, but still not insignificant.
From: Eric Smith on 19 May 2006 03:55 John Selck <selck_j(a)informatik.hgv-hamburg.de> writes: > Same opcodes but faster clockspeed. Also, CBM switched from NMOS to HMOS. HMOS is just NMOS with smaller process geometry. The NMOS to HMOS transition was a bigger change than for instance going from 1 micron to 0.8 micron CMOS, but not nearly as big a change as switching from PMOS to NMOS, or from NMOS/HMOS to CMOS.
From: Eric Smith on 19 May 2006 03:56 buchty(a)atbode100.lrr.in.tum.de (Rainer Buchty) writes: > There are quite some "it wouldn't work otherwise" examples, though, > which require those undocumented opcodes to meet strict timing. Such as?
From: John Selck on 19 May 2006 04:34 Am 19.05.2006, 08:48 Uhr, schrieb Pasi Ojala <albert(a)pikkukorppi.cs.tut.fi>: > On 2006-05-18, John Selck <gpjiweg(a)t-online.de> wrote: > > 0$: stx $fe00 > sbc $10 > bcs 1$ > adc $11 > inc 0$+1 > $1: > >> Best case: 19 vs 11 clock cycles (1.73x speed) >> Worst case: 23 vs 15 clock cycles (1.53x speed) > > Best case: 10 vs 11 clock cycles (0.9x speed) > Worst case: 18 (17 if zeropage) vs 15 cycles (1.2x or 1.13x speed) > >> Fact remains: illegals can make a difference on certain tasks. > > In best-case your routine is slower than without illegals, > and in average it is about the same speed. Yes true your routine is faster, but it does not do any Bresenham interpolation.
From: John Selck on 19 May 2006 04:51
Am 19.05.2006, 06:28 Uhr, schrieb mdj <mdj.mdj(a)gmail.com>: > Of course, the point remains though that your would never do this on > the Apple II series, as you'd limit your target market to the earliest > machine, rather than just the lowest common denominator of all machines > (64k, 6502 code that's documented and unbuggy) It's easy to do a processor check. |