Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!usc!samsung!caen!kuhub.cc.ukans.edu!markv From: markv@kuhub.cc.ukans.edu Newsgroups: comp.sys.amiga.hardware Subject: Re: Breaking through the chip-bus barrier? Message-ID: <1991May23.121032.31010@kuhub.cc.ukans.edu> Date: 23 May 91 17:10:32 GMT References: <1991May21.081806.2668@kberg.se> <1991May23.045536.1208@uniwa.uwa.oz> Organization: University of Kansas Academic Computing Services Lines: 50 In article <1991May23.045536.1208@uniwa.uwa.oz>, andreww@uniwa.uwa.oz (Andrew John Williams) writes: > svante@kberg.se (Svante Gellerstam) writes: > >>I would like to say that the highest hurdle to come over is the >>bitplane concept. > > Why bother? Bitplanes generally gives higher video bandwidth (just look > at Nat Semi's graphics chipset) and more importantly more processor - > memory bandwidth (If its done right - the processor sees 1 bit/pixel and > the hardware sorts out the rest) I disagree to some extent. The relative merits of "chunky pixel" versus bitplanes depends on the kind of work being done. For area drawing, filling, raster bitmaps being moved in whole, etc. the bitplane system is better because you can optimize things and only change certain bitplanes. However, for line drawing (esp non vertical/hoizontal), object graphics, and other mostly single pixel manipulations the chunky pixel is better from the CPUs point of view. Take for instance a WritePixel() function. It might have to access one bitplane, or it might have to access all. Plus, since there are several bits per byte, it must read and write each plane. With Chunky pixel mode, it only writes one byte and its done. (Assuming an even byte bit count per pixel). If you do some simple profiling and best/worse/average case scenarios, you'll see that the more bitplanes you have (ie: 12,18,24 bit systems), the worse bitplanes are versus chunky pixels. Finally, Commodore themselves have "endorsed" chunky pixels since that's what the 2610 uses (assuming it ships before computers become sentient and dont need it anymore :-)). As for the discussion on CHIP architechures, simply modifing CHIP RAM to use VRAMs and Denise to take her DMA from the serial shift lines would drastically speed up drawing, since the CPU and Blitter would get massivlely increased available bandwidth (esp in higer res/color modes). > John West (stealing Andrew's account) > ten green fish sitting on a wall (or was that pink fish?) > -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Mark Gooderum Only... \ Good Cheer !!! Academic Computing Services /// \___________________________ University of Kansas /// /| __ _ Bix: mgooderum \\\ /// /__| |\/| | | _ /_\ makes it Bitnet: MARKV@UKANVAX \/\/ / | | | | |__| / \ possible... Internet: markv@kuhub.cc.ukans.edu ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~