dcc6502

Disassembler for 6502 processors.

Table of Contents

• Features
• Sample Output
• HOWTO: Compile
• Bug Fixes
• History

Features

• Simple command-line interface
• Single file, ANSI C source
• Annotation for IO addresses of Nintendo Entertainment System (NES) system registers
• Apple 2 / Atari style output via -a
• Cycle-counting output via -c
• Machine code display inline with the disassembly via -d
• Skip 'n' beginnign bytes of binary via -b #
• Assembly style output via -s

Sample Output

NES output: dcc6502 -b 4 -d -o 0x900 -m 10 hgrbyte.bin

; Source generated by DCC6502 version v2.4
; For more info about DCC6502, see https://github.com/Michaelangel007/dcc6502
; FILENAME: hgrbyte.bin, File Size: $023B (571)
;     -> Hex output enabled
;---------------------------------------------------------------------------
                ORG $0900       ;
$0900> A9 10:   LDA #$10        ;
$0902> 2C 54C0: BIT $C054       ;
$0905> 2C 50C0: BIT $C050       ;
$0908> 2C 5300: BIT $0053       ;

Apple 2 output: dcc6502 -b 4 -d -o 0x900 -m 10 -a hgrbyte.bin

; Source generated by DCC6502 version v2.4
; For more info about DCC6502, see https://github.com/Michaelangel007/dcc6502
; FILENAME: hgrbyte.bin, File Size: $023B (571)
;     -> Hex output enabled
;     -> Apple II output enabled
;---------------------------------------------------------------------------
                ORG $0900       ;
0900:A9 10      LDA #$10        ;
0902:2C 54 C0   BIT $C054       ;
0905:2C 50 C0   BIT $C050       ;
0908:2C 53 00   BIT $0053       ;

HOWTO Compile

Compile via the de-facto make:

    make clean && make all

The included makefile has a bunch of options:

Option	Effect
clean	Delete binary files
all	Build code and binary test files
help	Show makefile help options
illegal	Build and test illegal 6502 opcodes
install	Build and copy to /opt/local/bin/disasm6502
zero	Build and test zero-length file

NOTE: The binary is installed into /opt/local/bin/ as disasm6502 in order not to over-write any previous versions of dcc6502.

Bug Fixes

• Cycle Timing

  • http://nesdev.com/6502_cpu.txt
  • https://github.com/ramiropolla/mame-ap2k/tree/master/src/emu/cpu/m6502

  Dcc6502 has the following cycle timing bugs that have been fixed in this fork:

Instruction	Opcode	Bad	Fixed
ROL abs,X	3E	7	6
LSR abs,X	5E	7	6
ROR abs,X	7E	7	6
STA (zp),Y	91	5	6
STA abs,Y	99	4	5
STA abs,X	9D	4	5

• Instruction decoding changed from naive linear O(151) to fast O(1)
• Fixed off-by-one file length bug
  • Files no longer disassemble one past their length
  • Zero length files now work properly
• Fixed slow reading file one byte at a time to a single, fast, read
• Fixed buffer overflow memory access
• Miscellanous code cleanup to make it easy to read

History

The original 1.0 version of dcc6502 was written overnight on Christmas eve 1998. At the time, I (Tennessee Carmel-Veilleux) was a 16-year-old NES hacker learning 6502 assembly. Of course, as many teenagers are, I was a bit arrogant and really thought my code was pretty hot back then :) Fast-forward 15 years and I'm a grown-up engineer who is quite a bit more humble about his code. Looking back, I think the tool did the job, but obviously, 15 years of experience later, I would have made it quite a bit cleaner. The disassembler has floated online on miscalleanous NES development sites since 1998. I decided to put it on github starting at version 1.4 and I will be cleaning-up the code over until version 2.0.

This disassembler has made the rounds and has been used for a lot of different purposes by many different people over the years. Hopefully it will continue to be useful going forward.

In 2017 AppleWin debugger developer Michael was looking for a simple disassembler for future "Apple Games Disassembly Projects." After seeing that the foundation was "good enough" he got involved fixing the poor performance, design, user experience, and miscellaneous bugs. A testament to the good C foundation -- not the typical bloatd C++ crap that is over-engineered that passes for these days.