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80 lines
2.6 KiB
Plaintext
80 lines
2.6 KiB
Plaintext
Ribos
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=====
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This little demo is intended to be a well-commented example of how to
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program a raster interrupt in 6502 assembly language on a Commodore 64.
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This (r)aster (i)nterrupt changes the colour of a region of the
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(bo)rder of the C64 (s)creen; thus, RIBOS. Also, it's the name of a
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planet from Dr. Who, if that means anything.
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How to Run the Demo (using the VICE C64 emulator, x64)
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------------------------------------------------------
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0. Obtain VICE from http://www.viceteam.org/, install it,
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and run x64
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1. Mount this project's directory as drive 8:
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Make sure
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Peripheral settings > Device #8 > Enable IEC Device
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is checked, then select
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Peripheral settings > Device #8 > File system directory...
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and enter the path to the project directory.
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2. LOAD "RIBOS.PRG",8,1
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3. SYS 49152
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4. You should see the colour of the middle of the border change
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while you get a READY. prompt and can continue working.
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How to Assemble the Program (using the p65 assembler)
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-----------------------------------------------------
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0. Obtain p65 from http://hkn.berkeley.edu/~mcmartin/P65/
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(I used p65-Perl version 1.1) and install it somewhere
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on your path. If your Perl interpreter isn't located at
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/usr/bin/perl, change the first line of p65 appropriately.
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1. p65 -v -t -b ribos.p65 ribos.prg
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The switches aren't necessary, but they make it feel like
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p65 is doing something difficult and important. It also
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isn't necessary to add the '.prg' extension on the end of
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the binary object's filename, since it will appear as a
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PRG file to VICE anyway, but it's nice as a reminder when
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you're working in a modern operating system.
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2. Follow the steps under 'How to Run this Demo' to see that
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it worked.
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How it Works
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------------
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Read the source! I've tried to make it very well-commented,
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including what happens when you leave out some steps.
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I wrote this demo because it was a long time since I had done any C64
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programming, and, having just obtained a copy of the 'Commodore 64
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Programmer's Reference Guide,' I wanted to code something challenging,
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yet not too involved. I remembered raster interrupts as one of those
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quintessential C64 low-level graphics tricks, so I decided to try my
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hand at that. Looking around on the Internet, I found this page:
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http://everything2.com/index.pl?node_id=79254
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Although it's a fairly detailed description, it took me a couple of
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frustrating hours to implement it successfully - both the everything2
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article and the Reference Guide were pretty muddy on a couple of
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points. What I learned in the process is written into the comments.
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Happy raster-interrupting!
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-Chris Pressey
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April 10, 2007
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Vancouver, BC
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