T430LCD

LCD Brightness, Aspect-Ratio and Pixel-Perfect Centering Control for the Lenovo ThinkPad T430 under Real MS-DOS

The tools can also work with other Ivy Bridge/Intel HD Graphics 4000 laptops. The complete utility set has been confirmed working on a Lenovo IdeaPad Yoga 13 with a Core i5-3427U and an HP EliteBook Folio 9470m with a Core i5-3427U.

Aspect ratio corrected DOOM:

Aspect ratio corrected Norton Commander:

Duke Nukem 3D in pixel perfect and centered 1024x768 mode on 1600x900 HD+ LCD:

T430LCD is an open-source collection of utilities that restores modern LCD functionality when running real MS-DOS on a Lenovo ThinkPad T430 with Intel HD Graphics 4000 (Ivy Bridge).

The project provides:

• Interactive LCD brightness control
• Automatic boot-time brightness initialization
• Automatic 4:3 aspect-ratio correction for legacy DOS video modes
• Pixel-perfect centered display mode based on the active Intel display-pipe source raster
• DPMI-compatible brightness and display-correction variants for memory-manager environments
• Reverse-engineering and diagnostic utilities
• Complete technical documentation

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Note

Current release: v2.4

Implemented

• ✔ LCD brightness control
• ✔ CONFIG.SYS brightness driver
• ✔ DPMI-compatible brightness control for EMM386/JEMM386 systems
• ✔ Automatic 4:3 aspect-ratio TSR
• ✔ Pixel-perfect centered /C policy
• ✔ FIR-91 sharp filtering with /AS and /S
• ✔ Runtime /A, /AS, /S and /C policy switching
• ✔ Built-in /? command help
• ✔ DPMI-compatible ASPECTD implementation
• ✔ Internal LCD support
• ✔ External VGA support
• ✔ External DVI support
• ✔ Reverse-engineering diagnostics
• ✔ Comprehensive documentation

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Features

Brightness

• BLCSET – Interactive LCD brightness control for plain DOS
• BLCSETD – DPMI-compatible version of BLCSET for systems using EMM386/JEMM386 and a resident 32-bit DPMI host such as HDPMI32
• BLCINIT – CONFIG.SYS device driver to set LCD brightness at boot time

Display fitting

• ASPECT – Plain-DOS TSR. With no argument it retains the historical /A behavior: centered 4:3 correction with Intel Medium 3×3 filtering. /AS uses the same 4:3 geometry with the hardware-verified FIR-91 sharp programmable filter, /S applies FIR-91 without changing the current fitter geometry, and /C selects pixel-perfect centered mode. /D deactivates, /E re-enables the selected policy, /U safely restores/deactivates before physically unloading, and /? shows a short command summary.
• ASPECTD – DPMI-compatible counterpart for systems using EMM386/JEMM386 and a resident DPMI host such as HDPMI32. It supports the same /A, /AS, /S, /C, /D, /E and /? model; /U remains a logical deactivation because the resident DPMI client cannot be safely destroyed later on the verified HDPMI32 path.

In /C mode the target is derived from Pipe A PIPESRC rather than from a hard-coded DOS resolution. This provides a true centered 1:1 source raster on the fixed internal LCD. Hardware testing also identified narrow legacy compatibility exceptions in /C: BIOS modes 00h/01h use 360×400 → 720×400 when that exact Pipe A source is observed, while modes 04h, 05h and 0Dh use 320×400 → 640×400. In both cases only the missing horizontal doubling is supplied.

Diagnostic Utilities

Brightness:

• BLCPWM
• OPREGPM

Display fitting:

• FITREAD
• PFDIAG
• PFSNAP

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Supported Hardware

The current project has been verified on:

Hardware	Internal LCD	Status
Lenovo ThinkPad T430	1600×900	✅ Fully verified primary platform; v2.4 /A, /AS, /S and /C development/testing platform
Lenovo IdeaPad Yoga 13, Core i5-3427U / Intel HD 4000	1600×900	✅ Complete utility set confirmed working
HP EliteBook Folio 9470m, Core i5-3427U / Intel HD 4000	1366×768	✅ Complete utility set confirmed working
Dell Inspiron E5550 / Intel HD Graphics 5500 (Broadwell)	1920×1080	✅ ASPECT confirmed; BLCSET does not work
Intel HD Graphics 4000 (Ivy Bridge)	—	✅ Verified on the systems above
External VGA monitor on T430	—	✅ Verified
External DVI monitor on T430	—	✅ Verified

The ThinkPad T430 remains the primary fully documented and officially supported platform. The IdeaPad Yoga 13 and EliteBook Folio 9470m are community-confirmed compatible with the complete T430LCD utility set. ASPECT has additionally been confirmed on a Broadwell Dell Inspiron E5550 with Intel HD Graphics 5500, but BLCSET does not work on that system. The detailed v2.3 centered-mode regression matrix is from the T430.

Confirmed /A internal-LCD geometry:

• ThinkPad T430, 1600×900 → 1200×900, centered at X=200, Y=0
• IdeaPad Yoga 13, 1600×900 → 1200×900, centered at X=200, Y=0
• EliteBook Folio 9470m, 1366×768 → 1024×768, centered at X=171, Y=0
• Dell Inspiron E5550 / Intel HD Graphics 5500, 1920×1080 → 1440×1080, centered at X=240, Y=0 (ASPECT confirmed)

The v2.4 /C implementation was additionally tested on the T430 with standard VGA, CGA/EGA legacy modes, VESA modes and non-standard VGA-register-compatible modes. The 640×200 and 640×350 CGA/EGA-family modes worked without special handling; the 320-wide legacy BIOS modes 04h, 05h and 0Dh use the narrow 320×400 → 640×400 horizontal-only correction described above.

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Repository Layout

T430LCD/
│
├── TOOLS/      End-user utilities
├── DIAG/       Reverse-engineering diagnostics
├── INCL/       Shared include files
├── BIN/        Optional compiled binaries
└── docs/       Project documentation

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Documentation

• User Guide
• Reverse Engineering
• Intel Registers
• Design Notes
• Development History
• Contributing
• Coding Conventions
• Hardware Tests

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Building

Requirements:

• Borland Turbo Assembler (TASM)
• Borland TLINK

Build everything:

BUILDALL

Clean generated files:

CLEANALL

Every utility also contains its own BUILD.BAT and CLEAN.BAT.

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Design Philosophy

• Perform read-only diagnostics before modifying hardware.
• Modify only the smallest verified register set.
• Keep hardware-sensitive code explicit and easy to audit.
• Validate every change on real hardware.
• Preserve diagnostic output needed for useful hardware reports.
• Preserve all reverse-engineering tools and documentation.

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Compatibility

Verified with:

• MS-DOS
• PC DOS
• FreeDOS

Brightness-tool compatibility:

• BLCSET is intended for plain DOS where its direct protected-mode MMIO path is available.
• BLCSETD provides the same interactive PWM duty control through DPMI and has been verified with JEMM386/HDPMI32.
• BLCINIT remains suitable for CONFIG.SYS use before EMM386/JEMM386 is loaded.

Display-correction TSR compatibility:

• ASPECT is intended for plain DOS without EMM386/JEMM386. No argument defaults to /A. /A selects 4:3 correction with Medium 3×3 filtering, /AS selects the same geometry with FIR-91 sharp filtering, /S selects FIR-91 filtering without changing geometry, /C selects pixel-perfect centering, /D deactivates, /E re-enables the selected policy, /U first performs the safe /D restore/deactivation path before physical unload, and /? prints help.
• ASPECTD provides the same policy model in DPMI environments and has been verified with JEMM386/HDPMI32. /U remains equivalent to /D and does not physically remove the resident DPMI client.

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External Links

• Latest Releases: https://github.com/Falcosoft/T430LCD/releases
• Repository: https://github.com/Falcosoft/T430LCD
• VOGONS discussion: https://www.vogons.org/viewtopic.php?t=111978

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License

Released under the MIT License.

See LICENSE.

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Development and attribution

This project was developed through an interactive collaboration:

• Zoltán Bacskó: problem definition, hardware investigation, compilation, testing on physical hardware, validation, and project maintenance.
• OpenAI ChatGPT (GPT-5.6): software implementation, debugging analysis, source-code generation, refactoring, and documentation drafting.

The code did not emerge as a one-shot generation. It was refined through repeated experiments on real Ivy Bridge hardware.

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Version History

v2.4

Major additions since v2.3:

• Added /AS, which keeps the proven /A 4:3 geometry but replaces Intel Medium 3×3 filtering with the hardware-verified FIR-91 programmable sharp filter.
• Added /S, which applies the same FIR-91 filter while preserving the current fitter position and size.
• Added /? short command help to ASPECT and ASPECTD.
• Added verified programming of the Ivy Bridge PF0 horizontal and vertical coefficient tables at 680A0h/680A4h and 680B0h/680B4h.
• FIR-91 uses the symmetric 4.4921875% / 91.015625% / 4.4921875% kernel for all phases.
• Sharp-mode table writes and filter-selector changes are read back and verified; any verification failure disables further writes for safety.
• Leaving /AS or /S restores Intel Medium 3×3 filtering while preserving unrelated PF_A_CTL bits.
• Refined the old PF_A_CTL rule: arbitrary/full-register rewrites remain unsafe, but v2.4 deliberately changes only the verified filter-selector bits required for /AS and /S. PF_A_VSCALE and PF_A_HSCALE remain untouched.
• Added the /C 40×25 text-mode compatibility fix: BIOS modes 00h/01h use 360×400 → 720×400 only when that exact Pipe A source geometry is observed.
• Reduced ASPECT resident memory by reusing the otherwise-unused PSP area below 0100h as the private interrupt stack and by replacing large literal FIR tables with compact generated templates.

v2.3

Major additions since v2.2:

• Added /A as the explicit 4:3 policy selector to both ASPECT and ASPECTD.
• Added /C pixel-perfect centered mode based on Pipe A PIPESRC.
• Added safe live switching between /A and /C when the current fitter state is owned by the TSR or is the saved fixed raster.
• Removed the old native-resolution VBE bypass. /A now consistently applies the 4:3 policy to successful native VBE modes; /C naturally preserves a native source at 1:1 full screen.
• Added the hardware-verified horizontal-only compatibility correction for legacy BIOS modes 04h, 05h and 0Dh when PIPESRC is exactly 320×400.
• Updated ASPECTD to keep a second read-only DPMI MMIO mapping for the Pipe A source page.
• Changed ASPECT /U to execute the safe /D restore/deactivation operation before physical unload.
• Shortened normal TSR status text while retaining detected output resolution and selected target window/position diagnostics.

v2.2

Major additions since v2.1:

• BLCSETD DPMI-compatible interactive LCD brightness control
• Added /D and /E runtime control to ASPECT while retaining /U as true physical unload
• Refactored ASPECT to reduce its resident memory footprint
• Extended JEMM386/HDPMI32 support to interactive brightness adjustment

v2.1

Major additions since v2.0:

• ASPECTD DPMI-compatible automatic aspect-ratio TSR
• JEMM386/HDPMI32 support for automatic aspect-ratio correction in protected-mode DOS environments

v2.0

Major additions since v1.0:

• BLCINIT CONFIG.SYS brightness driver
• ASPECT automatic aspect-ratio TSR
• Complete reverse-engineering diagnostic suite
• Comprehensive documentation
• Modular repository organization
• DOS-native build system
• Project coding conventions

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Contributions, hardware test reports, bug reports, and suggestions are always welcome.