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67f1a62596
Version 2.0, full emulation of 6502 op-codes, fully tested and functional. Extended description in ReadMe file. Bin2Hex tool to convert binary images to memory definition format. Microchess, EhBasic added.
263 lines
8.5 KiB
Plaintext
263 lines
8.5 KiB
Plaintext
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Project: MKBasic (VM6502).
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Author: Copyright (C) Marek Karcz 2016. All rights reserved.
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Free for personal and non-commercial use.
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Code can be distributed and included in derivative work under
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condition that the original copyright notice is preserved.
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For use in commercial product, please contact me to obtain
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permission and discuss possible fees, at: makarcz@yahoo.com
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This software is provided with no warranty.
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Purpose:
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MOS 6502 emulator, Virtual CPU/Machine and potentially retro-style 8-bit
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computer emulator.
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MOS-6502-compatible virtual computer featuring BASIC interpreter, machine code
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monitor, input/output device emulation etc.
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Program works in DOS/shell console (text mode) only.
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Makefile are included to build under Windows 32/64 (mingw compiler required)
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and under Linux Ubuntu or Ubuntu based.
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To build under Windows 32/64:
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* Install MINGW64 under C:\mingw-w64\x86_64-5.3.0 folder.
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* Run mingw terminal.
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* Change current directory to that of this project.
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* Run: makeming.bat
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To build under Linux:
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* Make sure C++11 compliant version of GCC compiler is installed.
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* Change current directory to that of this project.
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* Run: make clean all
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Program passed following tests:
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* 6502 functional test by Klaus Dormann
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* AllSuiteA.asm from project hmc-6502
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1. Credits/attributions:
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Parts of this project is based on or contains 3-rd party work:
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- Tiny Basic.
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- Enhanced Basic by Lee Davison.
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- Microchess by Peter Jennings (http://www.benlo.com/microchess/index.html).
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- 6502 functional test by Klaus Dormann.
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- All Suite test from project hmc-6502.
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2. Format of the memory image definition file.
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Program can load raw binary image of MOS 6502 opcodes.
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Binary image is always loaded from address $0000 and can be up to 64 kB long,
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so the code must be properly located inside that image.
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Depending on your favorite 6502 assembler, you may need to use proper command
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line arguments or configuration to achieve properly formatted binary file.
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E.g.: if using CL65 from CC65 package, create configuration file that defines
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memory segments that your 6502 code uses, then all of the segments (except the
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last one) must have attribute 'fill' set to 'yes' so the unsused areas are
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filled with 0-s.
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Two CFG files, one for microchess and one for All Suite from hmc-6502 project
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are supplied with this project and assembler source code adapted to be
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compiled with CL65.
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Other assemblers may need a different approach or may not be able to generate
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binary images that are required for this emulator.
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Program can also load memory image definition file (plain text), which is
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a format developed especially for this project.
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The format of the plain text memory image definition file is described below:
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; comments
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ADDR
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address
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data
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ORG
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address
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data
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IOADDR
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address
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ROMBEGIN
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address
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ROMEND
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address
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ENROM
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ENIO
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EXEC
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address
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Where:
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ADDR - label indicating that starting and run address will follow in
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the next line
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ORG - label indicating that the address counter will change to the
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value provided in next line
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IOADDR - label indicating that character I/O emulation trap address will
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follow in the next line
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ROMBEGIN - label indicating that the emulated read-only memory start address
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will follow in the next line
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ROMEND - label indicating that the emulated read-only memory end address
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will follow in the next line
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ENROM - enable read-only memory emulation
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ENIO - enable character I/O emulation
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EXEC - label indicating that the auto-execute address will follow
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in the next line
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address - decimal or hexadecimal (prefix $) address in memory
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E.g:
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ADDR
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$0200
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or
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ADDR
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512
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changes the default start address (256) to 512.
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ORG
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49152
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moves address counter to address 49152, following data will be
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loaded from that address forward
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data - the multi-line stream of decimal of hexadecimal ($xx) values
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of size unsigned char (byte: 0-255) separated with spaces
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or commas.
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E.g.:
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$00 $00 $00 $00
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$00 $00 $00 $00
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or
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$00,$00,$00,$00
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or
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0 0 0 0
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or
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0,0,0,0
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0 0 0 0
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Each described above element of the memory image definition file is optional.
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3. Character I/O emulation.
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Emulator has ability to simulate a 80x25 text output display device and
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rudimentary character I/O functions. The emulation is implemented by the means
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of trapping memory locations defined to be designated I/O emulation addresses.
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The default memory location is $E000 and also by default, the character I/O
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is disabled. It can be enabled from the debug console with 'I' command:
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I hexaddr
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E.g.:
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I E000
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or
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I FE00
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or by putting optional statements in the memory image dedinition file:
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ENIO
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or
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IOADDR
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address
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ENIO
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Where:
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address - decimal or hexadecimal (with prefix '$') address in memory
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$0000 - $FFFF.
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The same address is used for both, input and output operations.
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Reading from IOADDR inside the 6502 code invokes a blocking character
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input function from user's DOS/shell session.
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After user enters the character, the memory location contains the character
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code and also emulated CPU Acc register contains the same code.
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Reading from IOADDR+1 inside 6502 code invokes a non-blocking character
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input function from user's DOS/shell session.
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This function is different than blocking one in one respect.
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This function will return value 0 in the memory location and Acc register
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if there was no key pressed by the user (no character waiting in buffer).
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If there was a key typed, the function will act as the blocking counterpart.
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Writing to IOADDR inside the 6502 code will result in character code
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being put in the IOADDR memory location and also written to the character
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output buffer of the emulated display device. That character is not
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immediately transferred to the user's DOS/shell session. It is written to the
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emulated display's text memory instead. Depending on the mode in which
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emulator is currently working (continuous or step-by-step code execution),
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the emulated display device contents may or may not be updated on the user's
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screen in real time fashion. Remember that this is a DOS/shell console
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application. The user's console is shared among various functions of the
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program. In step-by-step mode, if the character I/O emulation is enabled, the
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current contents of the emulated display device can be displayed with
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corresponding debug console command: 'T'.
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4. ROM (read-only memory) emulation.
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This facility provides very basic means for memory mapping of the read-only
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area. This may be required by some 6502 programs that check for non-writable
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memory to establish the bounds of memory that can be used for data and code.
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One good example is Tiny Basic.
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By default the ROM emulation is disabled and the memory range of ROM is
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defined as $D000 - $DFFF.
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ROM emulation can be enabled (and the memory range defined) using debug
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console's command 'K':
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K [rombegin] [romend] - to enable
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or
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K - to disable
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The ROM emulation can also be defined and enabled in the memory image
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definition file with following statements:
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ROMBEGIN
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address
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ROMEND
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address
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ENROM
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5. Additional comments and remarks.
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IOADDR is permitted to be located in the emulated ROM memory range.
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The writing to IOADDR is trapped first before checking ROM range and writing
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to it is permitted when character I/O emulation and ROM are enabled at the
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same time. It is a good idea in fact to put the IOADDR inside ROM range,
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otherwise memory scanning routines like the one in Tiny Basic may trigger
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unexpected character input because of the reading from IOADDR during the scan.
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If you experience unexpected character input prompt while emulating
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6502 code, this may be the case. Reconfigure your IOADDR to be inside ROM in
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such case and try again.
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6. Warranty and License Agreement.
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This software is provided with No Warranty.
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I (The Author) will not be held responsible for any damage to computer
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systems, data or user's health resulting from using this software.
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Please use responsibly.
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This software is provided in hope that it will be be useful and free of
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charge for non-commercial and educational use.
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Distribution of this software in non-commercial and educational derivative
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work is permitted under condition that original copyright notices and
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comments are preserved. Some 3-rd party work included with this project
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may require separate application for permission from their respective
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authors/copyright owners.
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