T430LCD User Guide

1. Introduction

T430LCD addresses practical LCD/display problems under real DOS on physical Intel hardware:

restoring a preferred LCD brightness automatically at boot
preventing legacy 4:3 DOS modes from being stretched across a widescreen LCD
providing a pixel-perfect centered display mode for users who prefer the active source raster without additional fitter scaling

The primary development and validation platform is a physical Lenovo ThinkPad T430 with Intel HD Graphics 4000.

T430LCD v2.4 gives ASPECT and ASPECTD four explicit display policies:

/A — centered 4:3 aspect-ratio correction using Intel Medium 3×3 filtering
/AS — the same centered 4:3 geometry using the FIR-91 sharp programmable filter
/S — FIR-91 sharp filtering only, preserving the current fitter geometry
/C — pixel-perfect centered mode based on the active Intel display-pipe source raster

With no argument, ASPECT and ASPECTD retain the historical behavior and use /A.

The utilities use two MMIO access paths:

BLCSET and ASPECT use the direct plain-DOS protected-mode backend.
BLCSETD and ASPECTD use a 32-bit DPMI host and are intended for memory-manager environments such as the tested JEMM386/HDPMI32 configuration.

BLCINIT runs during CONFIG.SYS processing and is intended to set brightness before a memory manager is loaded.

2. Requirements

Verified hardware

Primary verified platform:

Lenovo ThinkPad T430
Intel HD Graphics 4000
internal 1600×900 LCD
external analog VGA output
external digital/DVI output

The complete T430LCD utility set has also been confirmed working on:

Lenovo IdeaPad Yoga 13 — Intel Core i5-3427U / Intel HD Graphics 4000 — internal 1600×900 LCD
HP EliteBook Folio 9470m — Intel Core i5-3427U / Intel HD Graphics 4000 — internal 1366×768 LCD

ASPECT has additionally been confirmed on:

Dell Inspiron E5550 — Intel HD Graphics 5500 (Broadwell) — internal 1920×1080 LCD — ASPECT confirmed; BLCSET does not work

These are community hardware confirmations. The Yoga 13 and EliteBook reports cover the complete utility set. The Dell Broadwell report is ASPECT-specific and should not be interpreted as brightness support because BLCSET was reported not to work. The detailed v2.3 /C regression matrix is from the primary ThinkPad T430.

Confirmed /A geometry includes:

System	Fixed-raster destination	Corrected 4:3 window	Position
ThinkPad T430	1600×900	1200×900	X=200, Y=0
IdeaPad Yoga 13	1600×900	1200×900	X=200, Y=0
EliteBook Folio 9470m	1366×768	1024×768	X=171, Y=0
Dell Inspiron E5550 / Intel HD 5500	1920×1080	1440×1080	X=240, Y=0

Software

Required for the direct plain-DOS tools:

real DOS on physical hardware
HIMEM/XMS
no active EMM386/JEMM386 virtual-8086 environment while running BLCSET or ASPECT

Required for the DPMI tools:

real DOS on physical hardware
a 32-bit DPMI host
the verified memory-manager configuration uses JEMM386/JEMMEX with resident HDPMI32

Borland TASM/TLINK are required only when building from source.

Not currently supported:

Windows DOS boxes or NTVDM
emulators without compatible physical Intel hardware access

Recommended plain-DOS baseline:

DEVICE=C:\DOS\HIMEM.SYS
DOS=HIGH

3. Installation layout

A convenient layout is:

C:\T430LCD\
    BLCSET.COM
    BLCSETD.COM
    BLCINIT.SYS
    ASPECT.COM
    ASPECTD.COM

You only need the variants appropriate for the configuration you actually use.

Diagnostics may be kept in:

C:\T430LCD\DIAG\
    FITREAD.COM
    PFDIAG.COM
    PFSNAP.COM

4. Brightness control

BLCSET

BLCSET is the interactive brightness utility for plain DOS.

Syntax:

BLCSET hexadecimal-value

Example:

BLCSET 0800

The value is hexadecimal. The primary tested T430 reported a maximum of 1155h.

Example values:

BLCSET 0040
BLCSET 0400
BLCSET 0800
BLCSET 1155

BLCSET locates Intel BAR0, detects the maximum PWM value, clamps the request, writes the active duty register, and verifies the readback.

Do not run BLCSET from an EMM386/JEMM386 virtual-8086 environment because its direct CR0/LGDT protected-mode transition is intentionally a plain-DOS path.

BLCSET is not a generic Intel-generation brightness utility. In particular, it was reported not to work on the Broadwell Dell Inspiron E5550 / Intel HD Graphics 5500 system on which ASPECT itself does work.

BLCSETD

BLCSETD provides the same interactive PWM duty control through DPMI.

Syntax:

BLCSETD hexadecimal-value

Examples:

BLCSETD 0040
BLCSETD 0800
BLCSETD 1155

BLCSETD preserves BLCSET's verified hardware policy:

BAR0 is discovered through PCI BIOS.
BAR0+48250h is read for CPU PWM control state.
BAR0+48254h is read for the current duty.
the upper 16 bits of BAR0+C8254h provide the detected maximum.
the requested duty is clamped to that maximum.
only BAR0+48254h is written.
its upper 16 bits are preserved.
the low 16-bit duty is read back and verified.

BLCSETD maps only the two 4 KiB MMIO pages required by the brightness path and releases its DPMI selectors and mappings before terminating.

BLCSETD has been verified with JEMM386/HDPMI32 on the ThinkPad T430.

5. BLCINIT

CONFIG.SYS syntax

DEVICE=C:\T430LCD\BLCINIT.SYS hexadecimal-value

Example:

DEVICE=C:\DOS\HIMEM.SYS
DEVICE=C:\T430LCD\BLCINIT.SYS 0800

BLCINIT sets brightness once during boot and then finishes initialization. It avoids repeatedly pressing the ThinkPad brightness hotkey, which may conflict with application shortcuts such as Norton Commander file-order controls.

BLCINIT is normally loaded before EMM386/JEMM386, so no DPMI-specific BLCINIT variant is needed.

6. ASPECT

ASPECT is the real-mode TSR for plain DOS.

Install with the default aspect policy

ASPECT

No argument is equivalent to selecting /A at installation.

Select aspect-ratio correction

ASPECT /A

/A selects the existing centered 4:3 correction algorithm. When ASPECT is already resident, /A switches the current policy back to aspect correction.

For a fixed-raster 1600×900 destination the calculated target is 1200×900 at X=200,Y=0. For 1366×768 it is 1024×768 at X=171,Y=0. A community Broadwell report confirms the same dynamic calculation on a 1920×1080 Dell Inspiron E5550 / Intel HD 5500, producing 1440×1080 at X=240,Y=0.

Like v2.3, v2.4 has no native-resolution VBE bypass. A successful native VBE mode is treated like any other compatible mode. Therefore a native 1600×900 VBE mode can be shown as 1200×900 centered when /A is selected.

Select sharp 4:3 aspect correction

ASPECT /AS

/AS uses the same dynamic centered 4:3 target geometry as /A, but programs the hardware-verified Ivy Bridge PF0 coefficient tables with the FIR-91 kernel and selects the programmable-filter mode. FIR-91 is a symmetric 3-tap kernel using approximately 4.4921875% / 91.015625% / 4.4921875% for every phase. The result is visibly sharper than the normal Intel Medium 3×3 filter while retaining the same aspect-corrected window size and position.

Select sharp filtering without changing geometry

ASPECT /S

/S programs the same FIR-91 filter but preserves the current PF_A_POS and PF_A_SIZE. This is useful when the BIOS or another display path has already chosen the desired geometry and only the scaling filter should change. The current size is rewritten unchanged only to latch the filter change.

Leaving /AS or /S for /A, /C, /D or /U restores the Intel Medium 3×3 filter. Filter/coefficient writes are verified by readback; a failure safety-locks further writes.

Select pixel-perfect centered mode

ASPECT /C

/C selects pixel-perfect centered mode. For a compatible fixed-raster output, ASPECT reads Pipe A PIPESRC at BAR0+6001Ch, decodes the source dimensions and centers that raster directly inside the detected fitter destination:

source width  = upper 16 bits + 1
source height = lower 16 bits + 1
X = (fixed width  - source width)  / 2
Y = (fixed height - source height) / 2

No extra even rounding is applied in /C. If one unused pixel remains because of an odd difference, it is left on the right or bottom side so that the source dimensions remain exact.

Examples on the 1600×900 T430 fixed-raster panel are:

Source raster	`/C` target	Position
720×400	720×400	X=440, Y=250
640×400	640×400	X=480, Y=250
640×480	640×480	X=480, Y=210
800×600	800×600	X=400, Y=150
1024×768	1024×768	X=288, Y=66
1600×900	1600×900	X=0, Y=0

The native 1600×900 case therefore becomes naturally pixel-perfect/full-screen in /C; no native-VBE special case is required.

Legacy CGA/EGA 320-wide exception

Hardware testing found one deliberately narrow exception to direct PIPESRC centering. Standard BIOS modes:

04h  CGA 320×200 4-color
05h  CGA 320×200 4-color
0Dh  EGA 320×200 16-color

can reach Pipe A in a 320×400 form where vertical doubling is already present but the horizontal doubling needed for correct centered display is absent.

For those BIOS mode numbers only, and only when PIPESRC decodes to exactly 320×400, /C changes the target to 640×400. Only the width is doubled. The same guarded principle is used for 40×25 text modes 00h and 01h: if and only if Pipe A reports exactly 360×400, the target becomes 720×400.

This is intentionally not a generic 320-wide rule. Other 320×200 VGA modes worked without it, and a non-standard VGA-register-compatible 320×400×256 Fractint mode also worked correctly and remains untouched. Standard 640×200 and 640×350 legacy modes likewise worked without special handling.

Short command help

ASPECT /?

The DPMI counterpart accepts ASPECTD /? and prints the corresponding short command summary.

Runtime policy switching

/A, /AS, /S and /C can be selected while ASPECT is resident. Immediate application is allowed only when ASPECT can prove that the fitter is either:

at the saved installation fixed-raster state, or
exactly at ASPECT's own last-applied position and size.

If neither condition is true, the selected policy is remembered but the current output is not overwritten; ASPECT waits for a later compatible BIOS mode set.

Deactivate without unloading

ASPECT /D

/D disables future correction while leaving the TSR resident. If the current PF_A_POS and PF_A_SIZE exactly match ASPECT's own last-applied state, ASPECT restores the installation-time fitter position and size. If the current fitter state belongs to another BIOS/output state, it is left untouched.

Re-enable

ASPECT /E

/E re-enables whichever policy (/A, /AS, /S or /C) is currently selected. If the current fitter state is compatible, the target is applied immediately; otherwise ASPECT waits for a later compatible mode set.

Physical unload

ASPECT /U

/U is the true physical unload command, but v2.3 first executes the same resident restore/deactivation operation used by /D while the MMIO engine and hooks are still available. Only after that operation reports a safe normal result does ASPECT restore interrupt vectors and free its memory.

If the restore/deactivation path reports a fitter verification failure, safety lock, busy state or control-protocol error, /U refuses to unload rather than discard a TSR whose display state may be uncertain.

ASPECT still unloads only when it is the newest handler on both INT 10h and INT 2Fh. If another TSR hooked either interrupt afterward, ASPECT refuses to unload to avoid breaking the chain.

AUTOEXEC.BAT example

@ECHO OFF
C:\T430LCD\ASPECT.COM
PATH C:\DOS;C:\UTIL

Fixed-raster safety rule

After a watched BIOS mode change, ASPECT applies the selected policy only when the post-BIOS PF_A_SIZE equals the fixed-raster size captured at installation. This avoids disturbing external/mode-timed output paths whose fitter size changes with the mode.

For live /A↔/C switching, ASPECT also accepts the exact last-applied state as owned state.

For /A and /C, ASPECT retains the established PF_A_POS → PF_A_SIZE geometry path. /AS and /S additionally program the verified PF0 coefficient tables and change only the filter-selector bits of PF_A_CTL; unrelated control bits are preserved. PF_A_VSCALE and PF_A_HSCALE are never modified. Pipe A PIPESRC is read only.

Mode changes watched

INT 10h AH=00h
INT 10h AX=4F02h

A failed VBE 4F02h call never triggers a fitting update.

7. ASPECTD

ASPECTD is the DPMI counterpart of ASPECT for systems using a resident 32-bit DPMI host.

Commands:

ASPECTD
ASPECTD /A
ASPECTD /AS
ASPECTD /S
ASPECTD /C
ASPECTD /D
ASPECTD /E
ASPECTD /U
ASPECTD /?

No argument defaults to /A; when already resident, the no-argument form reports resident state.

/A, /AS, /S, /C, /D, /E and /? have the same policy semantics as ASPECT. The display policy can be switched at runtime using the same ownership and verification rules.

For ASPECTD, /U and /D are logical deactivation commands. The DPMI client and interrupt hooks remain resident because the verified HDPMI32 environment does not provide a documented safe way to destroy this resident client context later.

ASPECTD uses two retained 4 KiB DPMI MMIO mappings:

the Fitter A page at BAR0+68000h for PF_A_POS and PF_A_SIZE
the Pipe A page at BAR0+60000h for the read-only PIPESRC value used by /C

The second mapping is retained even if ASPECTD starts in /A, so later runtime switching to /C does not require a new resident mapping operation.

A fitter write/readback failure permanently disables further ASPECTD writes until reboot.

8. Memory managers and DPMI

Plain-DOS backend

BLCSET and ASPECT use a direct protected-mode transition:

A20 is controlled through XMS.
a runtime GDT is installed.
the program enters 16-bit protected mode.
a flat selector accesses graphics MMIO.
the program returns to real mode.

This path must not be entered from EMM386/JEMM386 virtual-8086 mode.

DPMI backend

BLCSETD and ASPECTD avoid direct CR0/LGDT switching and use DPMI physical-memory mapping and selectors instead.

The ASPECTD development path was verified with a configuration of this form:

JEMMEX.EXE
HDPMI32.EXE -R
JEMMEX.EXE NOVCPI
VSBHDA.EXE
ASPECTD

The important points are that HDPMI32 is made resident before VCPI is disabled and that ASPECTD uses the resident DPMI host. BLCSETD can then use the same DPMI environment for one-shot brightness changes.

DPMI was preferred over a VCPI-only design because compatibility with VSBHDA was an explicit project goal.

9. Diagnostics

FITREAD

Reads Intel OpRegion panel-fitting fields.

PFDIAG

Reads all three Ivy Bridge panel-fitter blocks.

PFSNAP

Install:

PFSNAP /I

Clear:

PFSNAP /C

Run a graphics program, return to DOS, then dump:

PFSNAP /D

PFSNAP records requested BIOS modes, before/after state, fitter A/B/C registers, pipe timing registers, source sizes, and skipped VM86 captures.

Its Pipe A source measurements were important to the v2.3 /C design. For example, mode 13h was observed as a 640×400 PIPESRC, demonstrating that the Intel legacy VGA path can internally expand a lower logical VGA resolution before the panel fitter.

10. Troubleshooting

Immediate reboot or protection fault

With the current verified builds, an immediate reboot should not be expected.

For the direct tools, first check that EMM386/JEMM386 is not active and that you are using the final hardware-verified source. The direct CR0/LGDT transition is a plain-DOS path.

For a memory-manager configuration, use BLCSETD or ASPECTD with a resident 32-bit DPMI host instead of the direct variants.

Unsupported hardware or an obsolete experimental build can also cause failures.

BLCSETD or ASPECTD reports no DPMI host

Load a supported 32-bit DPMI host first. The verified configuration uses resident HDPMI32.

ASPECT reports that output is already 4:3

In /A this is expected for output paths whose installation-time fitter destination is already exactly 4:3. No correction hook is required for that policy.

/C is independent of the 4:3 test and can still be useful on a fixed-raster output because it centers the actual pipe source.

External display becomes garbled

Use the final conservative v2.3 ASPECT/ASPECTD builds. Older experimental builds applied startup-derived sizes more broadly and could disturb mode-dependent external outputs.

ASPECT /U refuses to unload

Possible reasons include:

another TSR owns INT 10h or INT 2Fh after ASPECT
the pre-unload /D restore/deactivation operation could not be completed safely
ASPECT is safety-locked after a fitter write/readback failure

Correct the later TSR chain or reboot as appropriate.

ASPECTD /U does not remove the TSR

This is expected. ASPECTD /U is a logical deactivation command, equivalent to /D; the DPMI client remains resident.

XMS MMIO test returns repeatable garbage

XMS function 0Bh handle-zero offsets are packed real-mode far pointers, not arbitrary 32-bit physical addresses. This mechanism cannot access MMIO near F0000000h.

11. Tested software and modes

Confirmed during development on the primary T430 include:

Plain-DOS ASPECT:

MS-DOS text mode
standard VGA programs
Duke Nukem 3D
Descent
v2.3 /C testing across VGA/VBE modes and the legacy CGA/EGA cases documented above

DPMI ASPECTD with JEMM386/HDPMI32:

Duke Nukem 3D
DOOM
/A and /C runtime policy control

Other confirmed use:

Norton Commander coexistence with boot-time brightness initialization
BLCSETD brightness adjustment with JEMM386/HDPMI32

12. Reporting results

Include:

Computer model:
CPU:
Integrated GPU:
Internal panel resolution:
Connection type:
DOS version:
HIMEM version:
EMM386/JEMM386 configuration:
DPMI host and version:
Utility and command:
Exact output:
Visible result:

For ASPECT/ASPECTD reports, include the detected output resolution and selected target window/position lines. For diagnostic reports, include complete output rather than selected lines.

13. License and attribution

T430LCD is licensed under the MIT License.

Zoltán Bacskó performed hardware investigation, compilation, testing, validation, and maintenance. OpenAI ChatGPT generated and refined implementation code, debugging analysis, refactoring, and documentation. Supported behavior is based on physical-hardware testing rather than emulator-only assumptions.

FilesExpand file tree

UserGuide.md

Latest commit

History