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.