Case study

gyx-decomp: Casio ES PLUS GYX firmware decompilation

gyx-decomp is a decompilation of the Casio ES PLUS GYX scientific calculator firmware, which runs on ROHM nX-U8/100 microcontrollers. Code Casio wrote in C is recovered as ANSI C that the CCU8 compiler turns into matching assembly, Casio assembly is disassembled and reworked for RASU8, and MCU startup code is recreated from files for other U8 parts. A build script compiles, links with RLU8, converts to Intel HEX and binary, and a features file switches modes and functions to build custom ROMs. Notes cover the memory model, compiler options, segment naming and link order.

Targets: Firmware
Category: Independent reconstruction cases
Relationship: Independent reconstruction project
Sources reviewed: 2026-11-09

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Requirements & limits

Prerequisites: Building needs Windows with the LAPIS U8/U16 Development Tools (CCU8 and the MACU8 Assembler Package), the bundled ML610904.DCL device file, and Python with the intelhex library for binary conversion.
Limits: The diagnostic test-select menu of GY454X VerF and GY455X VerF and the extra conversions of Japanese models are missing, and not all feature toggles are implemented.
Limits: Assembly comments, readable C and the RLU8 link order are still being worked on.
License: No licence file in the repository.

Cite

BibTeX

@misc{gyx-decomp-case,
  title = {{gyx-decomp: Casio ES PLUS GYX firmware decompilation}},
  howpublished = {\url{https://codeberg.org/gwetm/gyx-decomp}},
  url = {https://codeberg.org/gwetm/gyx-decomp},
  urldate = {2026-11-09},
  note = {Awesome REA entry: \url{https://awesomerea.org/resources/gyx-decomp-case/}}
}

Plain text

gyx-decomp: Casio ES PLUS GYX firmware decompilation. https://codeberg.org/gwetm/gyx-decomp (accessed 2026-11-09). Awesome REA entry: https://awesomerea.org/resources/gyx-decomp-case/

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