6502 illegal opcodes questions
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From: Paul Schlyter on 18 May 2006 10:14 In article <e4fdtv$2fj$1(a)rzsun03.rrz.uni-hamburg.de>, John Selck <selck_j(a)informatik.hgv-hamburg.de> wrote: > Michael J. Mahon wrote: .............. >> Non-portable code is written for two quite different reasons: >> >> 1) Because the coder doesn't even think about portability or >> doesn't understand it, non-portablility happens. >> 2) Because the coder understands perfectly, and chooses to >> write non-portable code on purpose. (One-time use, static >> platform, compelling need,...?) > > 3) Slow-as-hell 8 Bit platforms don't have a proper abstraction layer > for any of their hardware, no matter if sound, graphics, timers, ports > or CPU. ??????????????????? Could you point at one single case where use of undocumented opcodes did significantly speed up an application on the 6502 platform? -- ---------------------------------------------------------------- Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN e-mail: pausch at stockholm dot bostream dot se WWW: http://stjarnhimlen.se/
From: Cameron Kaiser on 18 May 2006 11:22 References trimmed. John Selck <selck_j(a)informatik.hgv-hamburg.de> writes: >Same opcodes but faster clockspeed. Also, CBM switched from NMOS to HMOS. Strictly speaking, HMOS *is* NMOS because they both still use n-type MOSFETs. -- Cameron Kaiser * ckaiser(a)floodgap.com * posting with a Commodore 128 personal page: http://www.armory.com/%7Espectre/ ** Computer Workshops: games, productivity software and more for C64/128! ** ** http://www.armory.com/%7Espectre/cwi/ **
From: Rainer Buchty on 18 May 2006 13:38 In article <e4htrq$1ktj$1(a)merope.saaf.se>, pausch(a)saaf.se (Paul Schlyter) writes: |> Could you point at one single case where use of undocumented opcodes did |> significantly speed up an application on the 6502 platform? Depends on how you define "significantly". If you understand it as "I want to see it on the stop-watch in my hand", then of course you won't find any. There are quite some "it wouldn't work otherwise" examples, though, which require those undocumented opcodes to meet strict timing. Rainer
From: Michael J. Mahon on 18 May 2006 15:29 Spiro Trikaliotis wrote: > Hello, > > aiiadict(a)gmail.com <aiiadict(a)gmail.com> schrieb: > > >>>It would actually be fun to see the real logic diagram of the 6502. >>>;-) >> >>I'd love to see it. > > > According to http://www.ncsu.edu/wcae/WCAE1/hanson.pdf (see also > http://www.ncsu.edu/wcae/WCAE1/), there must exist a blueprint at the > University of Mississippi, Department of Electrical Engineering. > > So, perhaps, there might be a source of a possible logic diagram > available, if someone could get in touch with that University? And the excellent detailed block diagram on the last page of Hanson's paper is a welcome addition to my library! -michael Music synthesis for 8-bit Apple II's! Home page: http://members.aol.com/MJMahon/ "The wastebasket is our most important design tool--and it is seriously underused."
From: John Selck on 18 May 2006 16:12
Am 18.05.2006, 16:14 Uhr, schrieb Paul Schlyter <pausch(a)saaf.se>: > Could you point at one single case where use of undocumented opcodes did > significantly speed up an application on the 6502 platform? Bresenham interpolation. Without illegal opcodes: STA $12 TXA STA $FE00,Y TAX LDA $12 SBC $10 BCS .skip ADC $11 INX ..skip With illegal opcodes: SHX $FE00,Y SBC $10 BCS .skip ADC $11 INX ..skip Best case: 21 vs 11 clock cycles (almost 2x speed with illegal) Worst case: 25 vs 15 clock cycles (still 1.67x speed) |