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294 lines
9.7 KiB
Markdown
294 lines
9.7 KiB
Markdown
SYMON - A 6502 System Simulator
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===============================
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**NOTE: THIS SOFTWARE IS UNDER ACTIVE DEVELOPMENT. Feedback is welcome!**
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**Version:** 0.9.9.1
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**Last Updated:** 27 July, 2014
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Copyright (c) 2014 Seth J. Morabito <web@loomcom.com>
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Portions Copyright (c) 2014 Maik Merten <maikmerten@googlemail.com>
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See the file COPYING for license.
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![Symon Simulator in Action] (https://github.com/sethm/symon/raw/master/screenshots/full.jpg)
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## 1.0 About
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Symon is a general purpose simulator for systems based on the MOS
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Technologies 6502 microprocessor and compatibles. Symon is implemented
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in Java. Its core goals are accuracy, ease of development, clear
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documentation, and extensive test suites for validating correctness.
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Symon simulates a complete system with a 1 MHz NMOS 6502, 32KB of RAM,
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16KB of ROM, a MOS 6551 or Motorola 6850 ACIA, a MOS 6522 VIA, and an
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experimental 6545 CRTC.
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Symon has extensive unit tests to verify correctness, and fully passes
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Klaus Dormann's 6502 Functional Test Suite as of version 0.8.2
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(See [this thread on the 6502.org Forums] (http://forum.6502.org/viewtopic.php?f=2&t=2241)
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for more information about this functional test suite).
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## 2.0 Requirements
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- Java 1.7 or higher
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- Maven 2.0.x or higher (for building from source)
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- JUnit 4 or higher (for testing)
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## 3.0 Features
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Symon can simulate multiple 6502 based architectures. At present, two
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machines are implemented: Symon (the default), and MULTICOMP.
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### 3.1 Memory Maps
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#### 3.1.1 Symon Memory Map
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- `$0000`--`$7FFF`: 32KB RAM
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- `$8000`--`$800F`: 6522 VIA
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- `$8800`--`$8803`: MOS 6551 ACIA (Serial Console)
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- `$9000`--`$9001`: MOS 6545 CRTC
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- `$C000`--`$FFFF`: 16KB ROM
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The CRT Controller uses memory address `$7000` as the start of Video
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memory.
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#### 3.1.2 MULTICOMP Memory Map
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- `$0000`--`$DFFF`: 56KB RAM
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- `$E000`--`$FFFF`: 8KB ROM
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- `$FFD0`--`$FFD1`: Motorola 6850 ACIA
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### 3.2 Serial Console and CPU Status
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![Serial Console] (https://github.com/sethm/symon/raw/master/screenshots/console.png)
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The main window of the simulator acts as the primary Input/Output
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system through a virtual serial terminal. The terminal is attached to
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a simulated ACIA, including a programmable baud rate generator that
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tries to approximate the correct "feel" of the programmed baud rate.
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(The sample Enhanced BASIC ROM image is programmed for 9600 baud)
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It also provides CPU status. Contents of the accumulator, index
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registers, processor status flags, disassembly of the instruction
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register, and stack pointer are all displayed.
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![Font Selection] (https://github.com/sethm/symon/raw/master/screenshots/font_selection.png)
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The console supports font sizes from 10 to 20 points.
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### 3.3 ROM Loading
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![ROM Loading] (https://github.com/sethm/symon/raw/master/screenshots/load_rom.png)
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Symon can load any appropriately sized ROM image. The Symon
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architecture expects as 16KB (16384 byte) ROM image, while the
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MULTICOMP architecture expects an 8KB (8192 byte) ROM image. Images
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are loaded via the "Load ROM..." action in the "File" menu. The
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selected ROM file will be loaded into memory at the correct ROM base
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address.
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### 3.4 Memory Window
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![Memory Window] (https://github.com/sethm/symon/raw/master/screenshots/memory_window.png)
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Memory contents can be viewed (and edited) one page at a time through the Memory Window.
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### 3.5 Trace Log
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![Trace Log] (https://github.com/sethm/symon/raw/master/screenshots/trace_log.png)
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The last 20,000 execution steps are disassembled and logged to the Trace Log Window.
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### 3.6 NEW - Experimental 6545 CRTC Video
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![Composite Video] (https://github.com/sethm/symon/raw/master/screenshots/video_window.png)
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This feature is highly experimental. It's possible to open a video window from the "View" menu.
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This window simulates the output of a MOS 6545 CRT Controller located at address `$9000` and
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`$9001`.
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By default, the 40 x 25 character display uses video memory located at base address `$7000`.
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This means that the memory from address `$7000` (28672 decimal) to `$73E8` (29672 decimal)
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is directly mapped to video.
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- Address Register (at address `$9000`)
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- R1: Horizontal Displayed Columns
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- R6: Vertical Displayed Rows
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- R9: Scan Lines per Row
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- R10: Cursor Start Scan Line and Cursor Control Mode
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- R11: Cursor End Scan Line
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- R12: Display Start Address (High Byte)
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- R13: Display Start Address (Low Byte)
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- R14: Cursor Position (High Byte)
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- R15: Cursor Position (Low Byte)
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Although the simulation is pretty good, there are a few key differences between
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the simulated 6545 and a real 6545:
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- The simulated 6545 supports only the straight binary addressing mode of the real 6545,
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and not the Row/Column addressing mode.
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- The simulated 6545 has full 16 bit addressing, where the real 6545 has only
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a 14-bit address bus.
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- The simulation is done at a whole-frame level, meaning that lots of
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6545 programming tricks that were achieved by updating the frame address
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during vertical and horizontal sync times are not achievable. There is no way
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(for example) to change the Display Start Address (R12 and R13) while a
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frame is being drawn.
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For more information on the 6545 CRTC and its programming model, please see the following resources
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- [CRTC 6545/6845 Information (André Fachat)] (http://6502.org/users/andre/hwinfo/crtc/index.html)
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- [CRTC Operation (André Fachat)] (http://www.6502.org/users/andre/hwinfo/crtc/crtc.html)
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- [MOS 6545 Datasheet (PDF)] (http://www.6502.org/users/andre/hwinfo/crtc/crtc.html)
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#### 3.6.1 Example BASIC Program to test Video
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This program will fill the video screen with all printable characters.
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10 J = 0
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20 FOR I = 28672 TO 29672
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30 POKE I,J
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40 IF J < 255 THEN J = J + 1 ELSE J = 0
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50 NEXT I
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60 END
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## 4.0 Usage
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### 4.1 Building
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To build Symon with Apache Maven, just type:
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$ mvn package
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Maven will build Symon, run unit tests, and produce a jar file in the
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`target` directory containing the compiled simulator.
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Symon is meant to be invoked directly from the jar file. To run with
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Java 1.5 or greater, just type:
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$ java -jar symon-0.9.1.0.jar
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When Symon is running, you should be presented with a simple graphical
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interface.
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### 4.2 ROM images
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The simulator requires a ROM image loaded into memory to work
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properly. Without a ROM in memory, the simulator will not be able to
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reset, since the reset vector for the 6502 is located in the ROM
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address space.
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By default, any file named `rom.bin` that exists in the same directory
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where Symon is launched will be loaded as a ROM image. ROM images can
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also be swapped out at run-time with the "Load ROM Image..." in the
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File menu.
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The "samples" directory contains a ROM image for the Symon
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architecture named 'ehbasic.rom', containing Lee Davison's Enhanced
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6502 BASIC. This serves as a good starting point for exploration.
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*Note*: Presently, EhBASIC only works with the Symon machine
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architecture, not with MULTICOMP.
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### 4.3 Loading A Program
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In addition to ROM images, programs in the form of raw binary object files can
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be loaded directly into memory from "Load Program..." in the File menu.
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Programs are loaded starting at addres $0300. After loading the program, the
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simulated CPU's reset vector is loaded with the values $00, $03, and the CPU is
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reset.
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There are two very simple sample program in the "samples" directory,
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for testing.
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- 'echo.prg' will echo back anything typed at the console.
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- 'hello.prg' will continuously print "Hello, 6502 World!" to the console.
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### 4.4 Running
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After loading a program or ROM image, clicking "Run" will start the simulator
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running.
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## 5.0 Revision History
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- **0.9.9.1:** 27 July, 2014 - Pressing 'Control' while clicking
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'Reset' now performs a memory clear.
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- **0.9.9:** 26 July, 2014 - MULTICOMP and multi-machine support
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contributed by Maik Merten <maikmerten@googlemail.com>
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- **0.9.1:** 26 January, 2014 - Support for IRQ and NMI handling.
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- **0.9.0:** 29 December, 2013 - First pass at a 6545 CRTC simulation.
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- **0.8.5:** 30 March, 2013 - ASCII display for memory window.
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Allows user to select a step count from a drop-down box.
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- **0.8.4:** 4 March, 2013 - Fix for ZPX, ZPY display in the trace log
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(change contributed by jsissom)
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- **0.8.3:** 12 January, 2013 - Added tool-tip text. Memory is no longer
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cleared when resetting. Fixed swapped register labels.
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- **0.8.2:** 01 January, 2013 - Fully passes Klaus Dormann's 6502 Functional Test suite!
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- **0.8.1:** 30 December, 2012
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- **0.8.0:** 29 December, 2012
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- **0.7.0:** 9 December, 2012
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- **0.6:** 5 November, 2012
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- **0.5:** 21 October, 2012 - Able to run Enhanced BASIC for the first time.
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- **0.3:** 14 October, 2012
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- **0.2:** 22 April, 2012
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- **0.1:** 20 January, 2010
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## 6.0 To Do
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- Feedback (in the form of dialogs, status bar, etc).
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- Better debugging tools from the UI, including breakpoints
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and disassembly.
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- UI needs a ton more polish.
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- More extensive testing.
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- Clean up JavaDoc.
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- Implement CMOS 65C02 instructions and NMOS / CMOS mode flag.
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- Allow displaying ACIA status and dumping ACIA buffers, for
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debugging.
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- Symbolic debugging.
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## 7.0 Acknowledgements
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This project would not have been possible without the following resources:
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- [Graham Edgecombe's JTerminal project] (https://github.com/grahamedgecombe/jterminal),
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which forms the core of Symon's console.
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- [Andrew Jacobs' 6502 Pages] (http://www.obelisk.demon.co.uk/6502/), for
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wonderfully detailed information about the 6502
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- [Neil Parker's "The 6502/65C02/65C816 Instruction Set Decoded"] (http://www.llx.com/~nparker/a2/opcodes.html),
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for information about how instructions are coded
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## 8.0 Licensing
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Symon is free software. It is distributed under the MIT License.
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Please see the file 'COPYING' for full details of the license.
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