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Supported Assemblers

Regenerator 2000 can generate assembly code compatible with several popular 6502 assemblers. This page lists the supported assemblers and the typical commands used to assemble the generated output.

64tass

64tass is a multi-pass optimizing macro assembler for the 65xx series of processors. It is known for its speed and advanced features.

Command Line

To assemble a file generated for 64tass:

64tass -o output.prg input.asm
  • -o: Specify the output filename.

ACME

ACME is a cross-assembler that supports the 6502, 6510, 65816, and other processors. It has been a standard in the C64 scene for many years.

Command Line

To assemble a file generated for ACME:

acme -f cbm -o output.prg input.asm
  • -f cbm: Set the output format to CBM (includes load address).
  • -o: Specify the output filename.

KickAssembler

KickAssembler is a popular Java-based assembler that features a powerful scripting language. It requires a Java Runtime Environment (JRE).

Command Line

To assemble a file generated for KickAssembler:

java -jar kickass.jar input.asm

KickAssembler automatically produces a .prg file by default.

Environment Variable

Because KickAssembler is a .jar file (not a standalone binary), --verify needs to know its absolute path. Set the KICKASS_JAR environment variable to the full path of the jar:

export KICKASS_JAR="$HOME/bin/KickAss.jar"

Add the line above to your ~/.zshrc, ~/.bashrc, or equivalent to make it permanent.

setx KICKASS_JAR "C:\Tools\KickAssembler\KickAss.jar"

If KICKASS_JAR is not set, Regenerator 2000 falls back to KickAss.jar in the working directory.

ca65

ca65 is the macro assembler included with the cc65 compiler suite. It is a powerful tool often used for larger projects requiring linking.

Command Line

Regenerator 2000 generates a single assembly file that can be assembled and linked in one step using the cl65 utility (included with cc65).

cl65 -t c64 -C c64-asm.cfg -o output.prg input.asm
  • -t c64: Set the target platform to Commodore 64 (sets up default memory configuration).
  • -C c64-asm.cfg: Uses the default configuration file for C64 assembly.
  • -o: Specify the output filename.

As long as the origin is $0801, the generated assembler will work Ok.

This is because, the config file c64-asm.cfg assumes that the start address is at $0801:

FEATURES {
    STARTADDRESS: default = $0801;
}
SYMBOLS {
    __LOADADDR__: type = import;
}
MEMORY {
    ZP:       file = "", start = $0002,  size = $00FE,      define = yes;
    LOADADDR: file = %O, start = %S - 2, size = $0002;
    MAIN:     file = %O, start = %S,     size = $D000 - %S;
}
SEGMENTS {
    ZEROPAGE: load = ZP,       type = zp,  optional = yes;
    LOADADDR: load = LOADADDR, type = ro;
    EXEHDR:   load = MAIN,     type = ro,  optional = yes;
    CODE:     load = MAIN,     type = rw;
    RODATA:   load = MAIN,     type = ro,  optional = yes;
    DATA:     load = MAIN,     type = rw,  optional = yes;
    BSS:      load = MAIN,     type = bss, optional = yes, define = yes;
}

If you are disassembling a file that has another origin, you will need to create your own config file. Just copy-paste the c64-asm.cfg, and make the needed changes. See ld65 "Configuration Files" section in the cc65 documentation.

Assembler Comparison

Regenerator 2000 abstracts away many assembler-specific differences, but some features use different directives depending on the target.

Fill Directives

When a range of memory contains identical values (and exceeds the Fill run threshold in Document Settings), Regenerator 2000 emits a fill directive instead of individual bytes.

Assembler Directive Example syntax
64tass .fill .fill 10, $00
ACME !fill !fill 10, $00
ca65 .res .res 10, $00
KickAssembler .fill .fill 10, $00

Scope Directives

Scopes allow you to reuse label names (like loop or next) in different parts of the program without conflicts.

Assembler Start Directive End Directive Notes
64tass .block .endblock
ACME !zone Limited scope support
ca65 .proc .endproc
KickAssembler .namespace .endnamespace

Verifying Exports

Regenerator 2000 includes a roundtrip verification mode that exports your project to all four assemblers, assembles each output, and compares the result byte-for-byte against the original binary. This ensures your disassembly is accurate and complete.

Usage

regenerator2000 --verify my_project.regen2000proj

The --verify flag implies --headless (no TUI is started). Only .regen2000proj files are supported.

Requirements

All four assemblers must be installed and available in your PATH:

Assembler Binary / Command Notes
64tass 64tass Must be in PATH
ACME acme Must be in PATH
ca65 (cc65) cl65 Must be in PATH
KickAssembler java -jar ... Requires KICKASS_JAR env var (see above)

If an assembler is not found, it is skipped (not counted as a failure). At least one assembler must be available for verification to succeed.

Example Output

Roundtrip Export Verification
=============================
  ✓ 64tass — byte-identical (2049 bytes)
  ✓ ACME — byte-identical (2049 bytes)
  ✓ ca65 — byte-identical (2049 bytes)
  ✓ KickAssembler — byte-identical (2049 bytes)

✓ All roundtrip verifications passed.