# 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.

- Type: Case study
- Targets: Firmware
- Category: Independent reconstruction cases
- Relationship: Independent reconstruction project
- Sources reviewed: 2026-11-09
- Added to the catalog: 2026-11-10
- Original resource: <https://codeberg.org/gwetm/gyx-decomp>
- Primary source: <https://codeberg.org/gwetm/gyx-decomp/src/commit/c8a8e72fad3a1f127db5dc9ee1ed7e19aefdb4fe/README.md>
- Catalog page: <https://awesomerea.org/resources/gyx-decomp-case/>
- Record JSON: <https://awesomerea.org/resources/gyx-decomp-case/record.json>
- Chinese version: [简体中文](https://awesomerea.org/zh/resources/gyx-decomp-case/index.md)

## 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.

## Primary sources

1. <https://codeberg.org/gwetm/gyx-decomp/src/commit/c8a8e72fad3a1f127db5dc9ee1ed7e19aefdb4fe/README.md>
2. <https://codeberg.org/gwetm/gyx-decomp/src/commit/c8a8e72fad3a1f127db5dc9ee1ed7e19aefdb4fe/build.bat>
3. <https://codeberg.org/gwetm/gyx-decomp/src/commit/c8a8e72fad3a1f127db5dc9ee1ed7e19aefdb4fe/CONTRIBUTING.md>
4. <https://codeberg.org/gwetm/gyx-decomp/src/commit/c8a8e72fad3a1f127db5dc9ee1ed7e19aefdb4fe/src/features/features.inc>
5. <https://codeberg.org/gwetm/gyx-decomp/src/commit/c8a8e72fad3a1f127db5dc9ee1ed7e19aefdb4fe/src/main.c>

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## About this entry

The description was reviewed against primary sources.
Original editorial content: MIT. Linked projects, papers and assets retain their own rights and licenses.