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symon/README.md
Seth Morabito 795ccfde5d CPU bug fixes and Simulator enhancements. 
Bug Fixes:

- Fixed several bugs in the CPU that caused processor status flags to
  be set incorrectly.  Instructions affected were: STA, STX, STY, CMP,
  CPX, CPY, BIT.

- Made some internal-use-only methods on the CPU class private.

- Fixed incorrect disassembly of (Indirect,X) and (Indirect),Y
  instructions. Although this didn't affect behavior, it certainly
  caused me some confusion in debugging.

- Added missing "BCS" instruction to instruction table.

Enhancements:

- Now includes a full version of Lee Davison's Enhanced 6502 BASIC
  bundled as source code and a ROM image. Get that REAL COMPUTER
  EXPERIENCE!(tm)

- If a file named "rom.bin" exists in the same directory where the
  simulator is executed, it will be loaded at addresses $d000-$ffff.

- Gave the CPU an idle loop to make simulated timing a little more
  realistic (but this is still an area needing major improvement)

- Changed the CPU's toString() method to give better debugging output.

- Added a small typeahead buffer to the Console.

- Better exception messaging.

Misc:

- Bumped version to 0.5, updated README.
2012-10-21 20:05:05 -07:00

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SYMON - A 6502 System Simulator

NOTE: THIS IS BETA QUALITY SOFTWARE UNDER ACTIVE DEVELOPMENT. Feedback is welcome!

Version: 0.5 Last Updated: 21 October, 2012

Copyright (c) 2008-2012 Seth J. Morabito <web@loomcom.com>

See the file COPYING for license.

1.0 About

Symon is a general purpose simulator for systems based on the NMOS Mostek 6502 microprocessor and compatibles. Symon is implemented in Java. Its core goals are accuracy, ease of development, clear documentation, and extensive test suites for validating correctness.

The initial goal is to simulate a system with an NMOS 6502 or CMOS 65C02 central processor; one or more 6522 VIAs; and one or more 6551 ACIAs. More functionality may be considered as time goes on.

2.0 Requirements

  • Java 1.5 or higher
  • Maven 2.0.x or higher (for building from source)
  • JUnit 4 or higher (for testing)

3.0 Usage

3.1 Building

To build Symon with Apache Maven, just type:

$ mvn package

Maven will build Symon, run unit tests, and produce a jar file in the 'target' directory containing the compiled simulator.

Symon is meant to be invoked directly from the jar file. To run with Java 1.5 or greater, just type:

$ java -jar symon-0.3-jar-with-dependencies.jar

When Symon is running, you should be presented with a simple graphical interface.

3.2 Loading A Program

Programs in the form of raw binary object files can be loaded directly into memory with the "Load" button.

Right now, all programs are loaded starting at addres $0300. After loading, the simulated CPU's reset vector is loaded with the values $00, $03, and the CPU is reset.

There are two very simple sample program in the "samples" directory, for testing.

  • 'echo.prg' will echo back anything typed at the console.

  • 'hello.prg' will continuously print "Hello, 6502 World!" to the console.

The sample directory also contains a ROM image of Lee Davison's Ehanced 6502 BASIC. For instructions on loading the rom, please see the README file in that directory.

3.3 ROM files

Any 12KB file named 'rom.bin' that exists in the same directory where Symon is launched will be loaded at address $d000. If the file is larger than 12KB, loading will fail. This functionality will be improved in a future release!

3.4 Running

After loading a program or ROM image, clicking "Run" will start the simulator running at address $0300.

4.0 To Do

  • Better debugging tools from the UI, including memory inspection, disassembly, breakpoints, and execution tracing.

  • Better ROM loading (and re-loading)

  • More accurate timing.

  • Interrupt handling!

  • UI needs a ton more polish.

  • More extensive testing.

  • Clean up JavaDoc.

  • Busses are defined by start address and length. Devices are defined by start address and end address. They should both use start/end address.

  • Implement CMOS 65C02 instructions and NMOS / CMOS mode flag.

  • Allow a flag to disable breaking to monitor on BRK.

  • Allow displaying ACIA status and dumping ACIA buffers, for debugging.

5.0 Licensing

Symon is free software. It is distributed under the MIT License. Please see the file 'COPYING' for full details of the license.