6502 illegal opcodes questions
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From: Spiro Trikaliotis on 20 May 2006 05:50 Hello, just some nit-picking: Linards Ticmanis <ticmanis(a)gmx.de> schrieb: > So once every line of characters the CPU has to stop for 40 cycles, so > that the character numbers can be read and stored. Then during the > normal video cycles only the character shapes are read. Color numbers > for the characters, on the other hand, are read in parallel from a > special SRAM with its own addressing lines going to the video chip. The color RAM has its own DATA lines, but the same address lines. It is D8-D11 on the VIC-II. Regards, Spiro. -- Spiro R. Trikaliotis http://cbm4win.sf.net/ http://www.trikaliotis.net/ http://www.viceteam.org/
From: Paul Schlyter on 20 May 2006 06:12 In article <op.s9uev3d6ru4cq2(a)news.t-online.de>, John Selck <gpjiweg(a)t-online.de> wrote: >Am 12.05.2006, 04:21 Uhr, schrieb Michael J. Mahon <mjmahon(a)aol.com>: > >> And in any case, depending on the peculiarities of a particular chip >> implementation is just asking to be locked out of future improvements. > >Like I stated several times now: You can easily do a processor check and >use different code. On plain 6502 you use the faster routine with illegals >and on 65816 etc you use a normal routine. It's 5 minutes work to do that. ....and how do you account for future versions of 6502 in that processor tests? That's of course a non-issue for the 6502, where there will be no future versions. But the issue is still valid for other processors where there may be future versions. -- ---------------------------------------------------------------- Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN e-mail: pausch at stockholm dot bostream dot se WWW: http://stjarnhimlen.se/
From: heuser.marcus on 20 May 2006 08:03 > LDIR eats 21 clock cycles per iteration, doing the same with other Z80 > instructions can be way faster. > > I tried to use the Z80 in the C128 for block copy/fill because I thought > "hey, it has a block copy command, so I guess it is fast" but it wasn't. > Then I tried normal opcodes, it was way faster than using LDIR but still > not faster than copying the stuff with the 8502. But if the 6502-designers had chosen to implement a block move then of course it would've been way faster! ;o) bye Marcus
From: Bruce Tomlin on 20 May 2006 09:20 In article <1148126608.168023.119240(a)38g2000cwa.googlegroups.com>, heuser.marcus(a)freenet.de wrote: > > LDIR eats 21 clock cycles per iteration, doing the same with other Z80 > > instructions can be way faster. > > > > I tried to use the Z80 in the C128 for block copy/fill because I thought > > "hey, it has a block copy command, so I guess it is fast" but it wasn't. > > Then I tried normal opcodes, it was way faster than using LDIR but still > > not faster than copying the stuff with the 8502. > > But if the 6502-designers had chosen to implement a block move then > of course it would've been way faster! ;o) You could speed up memory moves on the 6809 with the multiple register PSHS/PULS/PSHU/PULU instructions. They can move up to 10 bytes of registers plus the PC with only two instruction byte fetches (unlike LDIR which constantly branches back 2 bytes to read the opcode again), but for memory moves you need to use the other stack register for your destination, which means 8 bytes max. The trick is that you have to either disable interrupts or do things such that you can tolerate interrupts using either your source or destination memory for a stack. I dug up some old code of mine which scrolled a bitmap display (6K) by doing 256 loops, each with four moves of 6, 6, 5, and 5 bytes. (I was avoiding using the DP register because this code was for OS/9 or I could probably have done 8/8/6, but I still don't know why I was moving 22 bytes per loop instead of 23.) The difference between that and just doing a loop of LDD ,X++ / STD ,Y++ (which is still better than the Z80 because of the post-increment or 6502 because of 16 bits at a time) was enough to make the scrolling tolerable.
From: Laust Brock-Nannestad on 20 May 2006 10:29
heuser.marcus(a)freenet.de wrote: > Be careful or Captain Zilog crushes you! > http://www.milehighcomics.com/cgi-bin/backissue.cgi?action=fullsize&issue=14882664687%201 This was actually an ad for Zilog's Z8000 processor, not the Z80 :-) Regards, Laust |