This article was posted to the Usenet group alt.hackers in
1995; any technical information is probably outdated.
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Re: First Test Posting...
Article: 7843 of alt.hackers From: brain@msen.com (Jim Brain) Newsgroups: alt.hackers Subject: Re: First Test Posting... Date: 19 May 1995 16:04:22 -0400 Organization: Brain Innovations, Inc. Lines: 45 Sender: brain@garnet.msen.com Approved: brain@commodore-64.com Message-ID: kIBllmoZj8oJ079yn@msen.com Reply-To: brain@mail.msen.com NNTP-Posting-Host: garnet.msen.com Status: RO
In article <3phkql$2n7@news1.wolfe.net>, chrome@Wolfe.NET (Chrome) wrote: > Just a test post to see if my theory is right :) > > ObHack: Back in the 'Old Days' wrote up an 80 column screen driver for > Atari 8-bitters. Lovely slow bitmapped screens. Yeah, but I can better that: ObHack: 80 column bitmap screen drivers on 64 usually use a 4*8 grid for chars, and plot each on the bitmap. Works fine, except when scrolling, when one needs to move the screen all up by 8 lines. Well, there are two solutions on the Commodore 64: Use Ram Expansion Unit to do memory moves. Just stauff the 8k pixmap in REU at 1 byte/sec, and then pull it out 320 bytes higher in memory Line move in 16000 microseconds (.016 seconds). Better than 16*8000 microseconds for lda sta move of screen. Wrote this, but can't take credit for thinking of it first. Use character sets. Sure, a character set is only 256 chars, and there are 100 chars on a 64 screen, but you can flip char sets at any time, so... maps screen to be 2abcdefghijkl... THen, after 240 chars (6 lines), flip to next char set. Do this 5 times. Now, scrolling requires moving only the 1000 chars on the screen. Plotting is harder, but not by much. Very timing intensive, and must be very quick code. Did this one too, but can't take credit for it either. Jim > > -- > | chrome@wolfe.net My opinions are my own | > | http://www.wolfe.net/~chrome Noone else seems to want them | > | >>R.A.T. #1, Co-founder of the Institute of Reality Avoidance Therapy<< | > | ...don't ask me/I'm just improvising/my illusion of careless flight... | -- Jim Brain, Embedded Systems Designer, Brain Innovations. brain@msen.com Dabbling in VR, Old Commodore Computers, and Good Times! "The above views DO reflect my employer, since I am my employer" - Jim Brain
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