From: Jason Self <j@jxself.org>
Date: Fri, 31 Jul 2015 22:38:19 +0000 (-0700)
Subject: Adding initial work on Z-machine
X-Git-Url: https://jxself.org/git/?p=substrate.git;a=commitdiff_plain;h=ae0396abd3b3b68a03f678ca409e8528165c9383

Adding initial work on Z-machine
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diff --git a/documentation/z-machine.md b/documentation/z-machine.md
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+# Introduction
+This document covers the Z-machine, a virtual machine that was 
+developed in 1979 and used by Infocom for its text-based games. The 
+name came from their their first adventure, Zork.
+
+## Format
+This document is written using CommonMark, a markup language. More 
+information about CommonMark can be found at <http://commonmark.org>.
+
+## Copyright And Licensing
+Permission is granted to copy, distribute and/or modify this document 
+under the terms of the GNU Affero General Public License as published 
+by the Free Software Foundation ("FSF"), either version 3 of the 
+License, or (at your option) any later version published by the FSF.
+
+You should have received a copy of the GNU Affero General Public 
+License along with this document. If not see 
+<https://gnu.org/licenses/>.
+
+# Memory Map
+The Z-machine's memory map is made up of byte addresses that run from 
+0 on up. These addresses are then divided into the three regions of 
+dynamic, static and high.
+
+Dynamic memory starts at $00000 and must contain at least 64 bits 
+(with the first 64 known as the "header"). This portion then runs up 
+to the address before the word at $0e. It can be read or written with 
+either direct commands (GET, GETB, PUT, PUTB) or indirect (MOVE, 
+REMOVE). Because of this ease of access, it is legal for games to 
+alter the tables stored here and above the header.
+
+Immediately following the dynamic memory is static. This memory must 
+end by the last byte of the story file or by $0ffff, whichever comes 
+first. Unlike dynamic, it is illegal for games to write or attempt to 
+write to this memory. It can be read using GET and GETB. It is also 
+not defined anywhere, even in the header.
+
+Finally, high memory begins at what is known as the "high memory 
+mark," or the word at $04 in the header. Since it continues until the 
+end of the story file, it has the potential to overlap with the static 
+but never the dynamic. Unlike both the static and dynamic, it cannot 
+be accessed directly in any form by a game program. Its contents are 
+routines that can be called and strings that can be printed with 
+PRINT.