AHCINT - SATA AHCI Driver for Windows NT/2000/XP and Windows 95/98/Me

An AHCI (Advanced Host Controller Interface) SATA storage controller driver for Windows NT family and the Windows 95/98/Me, targeting operating systems from Windows 95 and Windows NT 3.1 up through Windows XP x64 Edition / Server 2003 x64 — long before Microsoft shipped a native AHCI driver.

Overview

AHCINT is a SCSI miniport driver built on the classic ScsiPort framework (SCSIPORT.PDR on Windows 9x/Me, scsiport.sys on the NT family). It talks directly to AHCI HBA/port registers (command lists, PRDTs, FIS structures) and translates SCSI requests from the Windows storage stack into ATA/ATAPI commands, so SATA AHCI controllers can be used as boot and data devices on operating systems that predate AHCI entirely.

Why?

Because plenty of real hardware only exposes its SATA ports in AHCI mode, and 9x/Me/NT/2000/XP have no idea what that is.

Features

AHCI 1.0-class hardware support
- HBA generic registers (GHC, IS, PI, CAP, CAP2) and per-port registers (CLB, FB, IS, IE, CMD, TFD, SIG, SSTS, SCTL, SERR, CI)
- Command List / Command Header / PRDT / FIS-based command submission
- Port state machine handling: COMRESET via SCTL.DET, FRE/ST start-stop sequencing, Command List Override (CLO) fallback when a port won't idle
- BIOS/OS Handoff Control (BOHC) so the driver takes ownership cleanly from the firmware
SCSI-to-ATA Translation Layer (SATL)
- INQUIRY, REQUEST SENSE, TEST UNIT READY, SYNCHRONIZE CACHE, VERIFY, MEDIUM REMOVAL, READ CAPACITY(10), MODE SENSE(6)
- READ/WRITE(6), READ/WRITE(10) and READ/WRITE(16) on all targets
- 64-bit SCSI on every target: READ CAPACITY(16) (SERVICE ACTION IN), READ/WRITE/VERIFY(16), SYNCHRONIZE CACHE(16), MODE SENSE(10) long LBA block descriptor (LLBAA); READ CAPACITY(10) returns 0xFFFFFFFF for disks past 2 TB so the upper layer switches to READ CAPACITY(16)
- ATA disks report INQUIRY VERSION 05h (SPC-3 / SBC-2, as nvme9x does), advertising 16-byte CDB support; VPD pages 00h and 80h (serial number from IDENTIFY)
- 28-bit READ/WRITE DMA whenever the request fits; READ/WRITE DMA EXT only on devices whose IDENTIFY DEVICE reports the 48-bit Address feature set (word 83, bit 10)
- ATAPI (PACKET command) pass-through for CD/DVD-class devices, alongside plain ATA disk support
- Real ATAPI media status: TEST UNIT READY / MEDIUM REMOVAL are passed through to the drive, REQUEST SENSE returns the drive's own sense data, and MODE SENSE(6) is translated to ATAPI MODE SENSE(10) and back — so media changes and empty trays are reported correctly to the CD-ROM class driver
- IDENTIFY DEVICE / IDENTIFY PACKET DEVICE based device enumeration, with cached string extraction for INQUIRY vendor/product fields
- Logical sector sizes of 512, 1024, 2048 and 4096 bytes (IDENTIFY word 106 / words 117–118): READ CAPACITY(10)/(16) and MODE SENSE report the drive's own block length, READ CAPACITY(16) also the logical-per-physical exponent (512e drives); see Logical sector size
Multi-target support from one source tree
- Windows 95 / 98 / Me (x86) — SCSIPORT.PDR miniport (ahcint9x.mpd)
- Windows NT 3.1 / 3.50 / 3.51 / NT 4.0 (x86) — ahcint.sys (one binary for all four)
- Windows 2000 / XP / Server 2003 (x86) and Windows XP x64 Edition / Server 2003 x64 (amd64) — ahcint.sys
- Every target uses the same synchronous Fast Polling I/O path; the few real differences are #ifdefs (see One source tree)

Architecture

          Windows 9x/Me                         Windows NT/2000/XP

        Application Layer                       Application Layer
               ↓                                       ↓
     IOS (I/O Supervisor) layers                SCSI Class Driver
               ↓                                       ↓
          SCSIPORT.PDR                            ScsiPort.sys
               ↓                                       ↓
  ahcint9x.mpd ← This driver               ahcint.sys  ← This driver
               ↓                                       ↓
               └─── AHCI Controller (PCI, 01-06-01) ───┘
                                   ↓
                   SATA disk / ATAPI optical drive

Key Components

src\ahcimain.c – Driver entry, PCI discovery (with bus-scan fallback), adapter/port initialization, HwStartIo, HwInterrupt, HwResetBus, DMA resource allocation; on 9X also HwAdapterState, the _MapPhysToLinear ABAR mapping and the VMM debug-print helper
src\ahcisatl.c – SCSI command dispatch, SCSI↔ATA/ATAPI translation, 28/48-bit command selection, INQUIRY/READ CAPACITY/MODE SENSE synthesis, sense handling, PRDT construction, the Fast Polling command engine
src\ahcint.h – Target switches (AHCI_W9X, AHCI_NT4), AHCI register layout, command/FIS structures, device extension, shared constants
*src\9X* – build.bat, NMAKE makefile (includes the DDK's MASTER.MK) and ahcint9x.lnk for Windows 9x/Me
*src\NT* – build.bat for NT 3.1/3.50/3.51/4.0
*src\2KXP* – sources / makefile / ahcint.rc for the DDK build utility (2000/XP/2003, x86 and amd64)
ahcint.inf / txtsetup.oem / oemsetup.inf / AHCINT9X.INF – Installation files (in bin\) (see Installation)

All targets compile the same three files in src\; the per-target folders only hold build files.

Feature matrix by target

	95/98/Me (x86)	NT 3.1/3.50/3.51/4.0 (x86)	2000/XP/2003 (x86) and XP x64/2003 x64 (amd64)
Build folder (sources are shared in `src\`)	`src\9X`	`src\NT`	`src\2KXP`
Target define	`AHCI_W9X` (implies `AHCI_NT4`)	`AHCI_NT4`	none
Driver binary	`ahcint9x.mpd` (`SCSIPORT.PDR` miniport)	`ahcint.sys`	`ahcint.sys`
I/O model	Synchronous Fast Polling — `HwStartIo` polls `PxCI`/`PxIS`/`PxTFD` every 10 µs, up to the SRB's `TimeOutValue` minus 1 s (see Command timeout)	Same	Same
Interrupt usage	None — `PxIE` = 0 and `GHC.IE` off; `HwInterrupt` only acknowledges stray status	Same; on NT 3.1 no interrupt is connected at all	Same
Max AHCI ports	8 (build-time, see Build-time limits)	8 (build-time)	8 (build-time)
Max AHCI controllers	8 (build-time, see Build-time limits)	8 (build-time)	8 (build-time)
PCI detection	Class code `01-06-01` plus known AMD/Intel device IDs; the bus:slot `SCSIPORT.PDR` hands in first, then a PCI bus-scan fallback	Same, bus:slot from ScsiPort first, then bus-scan fallback; NT 3.1 (no PCI support in its HAL) reads config space through ports `CF8h`/`CFCh`	Same, PnP-assigned bus:slot first, then bus-scan fallback
ABAR (MMIO) mapping	VMM `_MapPhysToLinear`, non-cached (KB Q169584 workaround)	`ScsiPortGetDeviceBase`	`ScsiPortGetDeviceBase`
ATA read/write commands	READ/WRITE DMA (28-bit) when the request ends below LBA 2^28 and moves ≤ 256 sectors; READ/WRITE DMA EXT only if IDENTIFY reports 48-bit support	Same	Same
READ/WRITE(16), READ CAPACITY(16), INQUIRY VERSION 05h (SPC-3)	Yes	Yes	Yes
Addressable capacity	2^48 sectors (ATA limit) via READ CAPACITY(16); what the OS class driver can use is up to the OS	Same	Same
REQUEST SENSE	Yes — ATA errors (e.g. LBA out of range, UNC) are reported here; ATAPI asks the drive	Same	Yes
Auto-sense on error (`SRB_STATUS_AUTOSENSE_VALID`)	No — class driver issues REQUEST SENSE	No — class driver issues REQUEST SENSE	Yes — ATA errors mapped from `PxTFD`, ATAPI sense fetched from the drive
ATAPI (PACKET) support	Yes	Yes	Yes
ATAPI MODE SENSE(6)→(10) translation	Yes	Yes	Yes
64-bit addressing (S64A)	No — 32-bit DMA only	No — 32-bit DMA only	Yes — 64-bit DMA when `CAP.S64A` is set (ABAR itself is read as a 32-bit BAR)
Hot-plug / late device detection	No	No	No
PRDT entries per command	64 (33 at most in use: 32 physical breaks)	64	64
DMA arena size	64 KB (shared across ports)	64 KB (shared across ports)	64 KB (shared across ports)
Max transfer size per I/O	~128 KB	~128 KB	~128 KB
Debug output	VMM `_Debug_Printf_Service` (`DEBUG=1` builds), prefix `[ahcint9x]`	`DbgPrint`, prefix `[AHCINT]`	`DbgPrint`, prefix `[AHCINT]`

Known Limitations

No NCQ (Native Command Queuing) — PxSACT is defined but never used; every port issues one command at a time via slot 0
No interrupt-driven completion — every target completes commands by Fast Polling; no MSI/MSI-X support
A slow command keeps the CPU that issued it busy polling for as long as it takes, up to the SRB timeout (see Command timeout)
~128 KB maximum transfer size per request (32 physical breaks), well short of AHCI's theoretical per-PRDT 4 MB limit
No hot-plug support on any target; devices are detected once, at HwInitialize
No power management (no device sleep/spin-down handling, no S3/S4 resume path beyond what ScsiPort provides)
Single-queue-depth design — no per-port command queuing beyond the one in-flight command AHCINT itself tracks
Disks past 2 TB need an upper layer that issues 16-byte CDBs (e.g. LBA64HLP.VXD on Windows 9x); the driver answers them on every target
Logical sectors larger than 4096 bytes are not taken (the port is left unusable); CHS-only devices (no LBA) are not addressable (SATA requires LBA)
A disk with logical sectors larger than 512 bytes works as a data disk only: BIOS INT 13h and the boot loaders read 512-byte sectors, so the system cannot boot from it
SYNCHRONIZE CACHE and VERIFY are completed without issuing an ATA command
9X and NT builds do not fill auto-sense; the OS-era class drivers issue their own REQUEST SENSE
Windows 95 RTM: see the SCSIPORT.PDR note below

Building from source

Requirements

Windows 95 / 98 / Me (x86):
- A Windows 9x build machine (the build script is written for the Windows 9x COMMAND.COM batch interpreter)
- Windows 95 DDK — expected at C:\DDK (provides MASTER.MK, BLOCK\INC, INC32, BLOCK\LIB\scsiport.lib)
- Win32 SDK for Windows NT 4.0 / Windows 95 — expected at C:\MSTOOLS
- Microsoft Macro Assembler (MASM) 6.11 — expected at C:\MASM611 (BIN\ML.EXE, BIN\NMAKE.EXE)
- Microsoft Visual C++ 2.0 — expected at C:\MSVC20 (BIN\CL.EXE, BIN\LINK.EXE, BIN\NMAKE.EXE)
Windows NT 3.1 / 3.50 / 3.51 / NT 4.0 (x86): Windows NT 4.0 DDK + Visual C++ 4.0 (MSVC 4.0)
Windows 2000 / XP (x86): Windows Server 2003 SP1 DDK ("WDK 6001", build 3790.1830)
Windows XP x64 / Server 2003 x64 (amd64): A DDK/WDK with an amd64 ("WNET") cross-compiler — Windows Server 2003 SP1 DDK ("WDK 6001", build 3790.1830), Windows Server 2003 R2 DDK, or the Windows 7 WDK (WinDDK 7600.16385.1)

Build Instructions

For Windows 95 / 98 / Me (x86)

build.bat expects a copy of the repository's src folder in C:\AHCINT (shared sources in C:\AHCINT, build files in C:\AHCINT\9X), and ahcint9x.lnk links against C:\DDK\BLOCK\LIB\scsiport.lib. If your tools live elsewhere, edit the SET lines at the top of build.bat (MASM_ROOT, C16_ROOT, C32_ROOT, SDKROOT, DDKROOT, AHCI_ROOT) and the library path in ahcint9x.lnk.

REM Copy the src folder (shared sources + 9X build files) to C:\AHCINT
mkdir C:\AHCINT
mkdir C:\AHCINT\9X
copy <path-to-AHCINT>\src\*.* C:\AHCINT
copy <path-to-AHCINT>\src\9X\*.* C:\AHCINT\9X

C:
cd \AHCINT\9X

REM Optional: debug build (debug output through VMM, see Debugging)
REM set DEBUG=1

REM Build
build.bat

build.bat sets MASTER_MAKE=1 and the tool roots, puts MASM 6.11 and Visual C++ 2.0 on PATH, creates TMP/TEMP (default C:\WINDOWS\TEMP) if they are missing, warns if any expected tool is not found, and then runs nmake in C:\AHCINT\9X. The makefile pulls in the DDK's MASTER.MK (BUILD_BITS=32, BUILD_TYPE=block), compiles ..\ahcimain.c and ..\ahcisatl.c with -DAHCI_W9X, and links them with ahcint9x.lnk.

Output: C:\AHCINT\9X\ahcint9x.mpd (plus ahcint9x.map). Run nmake clean to remove build output.

For Windows NT 3.1 / 3.50 / 3.51 / NT 4.0 (x86)

cd <path-to-AHCINT>\src\NT
build.bat

build.bat sets MSVCDIR (default C:\MSDEV) and DDKDIR (default C:\NT4DDK) — edit them if your tools live elsewhere — then compiles ..\ahcimain.c and ..\ahcisatl.c with -DAHCI_NT4 and links against scsiport.lib and ntoskrnl.lib.

Output: src\NT\ahcint.sys, for Windows NT 3.1 and later (-subsystem:native,3.50; the NT 3.1 loader does not check the subsystem version). The NT build imports only functions NT 3.1's SCSIPORT.SYS exports, so it must not call ScsiPortSetBusDataByOffset.

For Windows 2000 / XP (x86)

REM Set up build environment
Start Menu → Windows Server 2003 DDK → Build Environments → Windows 2000/XP Free Build Environment
REM (runs setenv.bat, configuring PATH/INCLUDE/LIB/DDKBUILDENV for the target)

REM Navigate to driver directory
cd <path-to-AHCINT>\src\2KXP

REM Build
build -cZ

sources compiles the shared ..\ahcimain.c and ..\ahcisatl.c (no target define). -c forces a clean rebuild and -Z prints full build output to the console. Output: obj\i386\ahcint.sys (checked) or obji386\ahcint.sys (free), depending on the environment chosen. Use the checked environment for a debug build (asserts enabled, unoptimized), free for release.

For Windows XP x64 / Server 2003 x64 (amd64)

The x64 driver is built from the same src\2KXP folder as the x86 driver; only the build environment differs.

REM Set up build environment
Start Menu → Windows Server 2003 (WNET) DDK/WDK → Build Environments → x64 Free Build Environment
REM (runs setenv.bat ... WNET AMD64, configuring the amd64 cross-tools and libraries)

REM Navigate to driver directory
cd <path-to-AHCINT>\src\2KXP

REM Build
build -cZ

Output: ahcint.sys under the amd64 output directory (objfre_wnet_amd64\amd64\ or equivalent, depending on the exact DDK/WDK version). ahcint.rc supplies version-resource information for this target.

The 2000/XP and x64 builds should first be verified in the checked build environment before being rebuilt and shipped from the free build environment.

Installation

Installation Media

Prebuilt binaries and install files live under bin\:

bin\
├── 9X\
│   ├── AHCINT9X.INF          (Windows 95/98/Me install file)
│   └── AHCINT9X.MPD          (SCSIPORT.PDR miniport)
├── NT\
│   ├── oemsetup.inf
│   ├── ahcint.sys
│   └── floppy\               (NT 3.50/3.51/4.0 driver disk)
│       ├── disk1             (tag file)
│       ├── oemsetup.inf
│       ├── txtsetup.oem
│       └── ahcint.sys
└── 2KXP\
    ├── ahcint.inf            (one INF for x86 and x64)
    ├── ahcint.sys            (x86 binary)
    ├── i386\
    │   └── ahcint.sys        (x86 binary)
    ├── amd64\
    │   └── ahcint.sys        (x64 binary)
    ├── floppy_i386\          (F6 disk, 2000/XP/2003 x86)
    │   ├── disk1             (tag file)
    │   ├── txtsetup.oem
    │   ├── ahcint.inf
    │   ├── ahcint.sys
    │   └── i386\ahcint.sys
    └── floppy_amd64\         (F6 disk, XP x64/2003 x64)
        ├── disk1             (tag file)
        ├── txtsetup.oem
        ├── ahcint.inf
        ├── ahcint.sys
        └── amd64\ahcint.sys

All three INF/OEM files match the controller by PCI class code (PCI\CC_010601, Mass Storage - SATA - AHCI).

Installing

Windows 95 / 98 / Me

Windows 9x/Me setup itself runs through the BIOS (INT 13h), so there is no F6-style driver step — install AHCINT9x once Windows is up. Because AHCINT9X.INF matches PCI\CC_010601, Windows may offer the controller in the New Hardware Found wizard on its own; otherwise install it manually:

Open Control Panel → Add New Hardware, let the wizard continue, and choose to select the hardware from a list.
Pick SCSI controllers, click Have Disk, and point it at bin\9X\ (AHCINT9X.INF).
Select AHCINT9x SATA AHCI Storage Controller and reboot. AHCINT9X.MPD is copied to WINDOWS\SYSTEM\IOSUBSYS.

If the protected-mode driver fails to load, Windows 9x falls back to MS-DOS compatibility mode for the affected disks (check Device Manager → Performance and BOOTLOG.TXT).

Windows 95 RTM users: if the controller shows a yellow exclamation mark in Device Manager, the original Windows 95 SCSIPORT.PDR is the problem. Either install the AMDK6 Update, or extract SCSIPORT.PDR from that update and copy it to WINDOWS\SYSTEM\IOSUBSYS yourself — rename the existing SCSIPORT.PDR there to SCSIPORT.BKP first so you keep a backup.

GUI-mode setup (Windows 2000/XP/XP x64/Server 2003)

Use bin\2KXP\ahcint.inf with "Have Disk" during a manual driver install. The same INF serves both architectures: it copies i386\ahcint.sys on x86 and amd64\ahcint.sys on x64. The device shows up as AHCINT SATA AHCI Storage Controller (x86) or AHCINT SATA AHCI Storage Controller (x64), and the driver installs as service AHCINT under LoadOrderGroup = SCSI Miniport.

Text-mode (F6) setup — Windows 2000/XP/XP x64/Server 2003

Copy the contents of bin\2KXP\floppy_i386\ (x86) or bin\2KXP\floppy_amd64\ (x64) onto a floppy disk (or a virtual floppy image for VM installs), press F6 at the start of text-mode setup, and select AHCINT SATA AHCI Storage Controller (ages2001) — or AHCINT SATA AHCI Storage Controller x64 (ages2001) on x64. Required whenever the install disk itself sits behind the AHCI controller.

Windows NT 3.1 / 3.50 / 3.51 / NT 4.0

NT uses the older OEM Setup mechanism (oemsetup.inf) rather than a standard .inf/.cat pair. Use "Have Disk" during setup (GUI-mode) or the equivalent F6 OEM prompt (text-mode), point it at bin\NT\floppy\, and select AHCINT SATA AHCI Storage Controller (ages2001).

boot.ini on Windows NT 3.1: both ARC paths work. multi(0)disk(0)rdisk(0)partition(1)\WINNT makes NTLDR read through the BIOS (INT 13h), so the BIOS has to boot from the AHCI disk. scsi(0)disk(0)rdisk(0)partition(1)\WINNT (disk(n) = AHCI port number) makes NTLDR drive the controller itself through NTBOOTDD.SYS, a copy of ahcint.sys in the root of the system partition; this works with NT 3.1's own NTLDR and with the Windows 2000 NTLDR/NTDETECT.COM.

Booting Windows NT 3.1 from an AHCI disk: NT 3.1's scsidisk (SCSI disk class driver) must be a boot driver (Start = 0), otherwise NTLDR does not load it and the system stops with 0x7B INACCESSIBLE_BOOT_DEVICE. Text-mode setup sets this when it installs onto a SCSI disk; when moving an existing installation onto the AHCI controller, set HKLM\SYSTEM\CurrentControlSet\Services\scsidisk\Start to 0 first (and AHCINT's own Start to 0).

Configuration

Registry values set at install time on the NT family (ahcint.inf service section, txtsetup.oem [Config.scsi.AHCINT], oemsetup.inf):

Tag – boot-load ordering tag: 40 on 2000/XP/x64, 33 on NT 3.1/3.50/3.51/4.0
Group – SCSI Miniport
Type / Start / ErrorControl – 1 (SERVICE_KERNEL_DRIVER) / 0 (boot start) / 1 (normal)
Event log – IoLogMsg.dll registered as the event message file (TypesSupported = 7)
2000/XP/x64 only – Parameters\PnpInterface\5 = 1 (PnP on the PCI bus). Set by ahcint.inf; when it is missing, the driver creates it itself at load (see Windows 2000/XP/x64 specifics)

On Windows 9x/Me, AHCINT9X.INF registers the controller with DevLoader = *IOS and PortDriver = AHCINT9X.MPD (plus DontLoadIfConflict = Y); there are no extra settings to configure.

Build-time limits

The port and controller limits are compile-time constants in src\ahcint.h. The defaults are 8 and 8; change them and rebuild if your hardware needs more.

#define MAX_SUPPORTED_PORTS             8       /* AHCI ports per controller */
#define AHCI_MAX_CONTROLLERS            8       /* AHCI controllers per system */

MAX_SUPPORTED_PORTS is a port number limit, not a port count: ports are addressed by their index in the HBA's PI (Ports Implemented) register, and every port whose index is MAX_SUPPORTED_PORTS or higher is ignored, even if the controller has fewer ports in total. A chipset that implements only ports 0, 1, 8 and 9 needs a value of at least 10 to see all four. Each port becomes one SCSI target ID (port 0 = target 0, and so on). AHCI allows at most 32 ports, so the useful range is 1–32.

Raising it has these consequences, all in src\ahcint.h and src\ahcimain.c:

DMA arena – every port takes 4 KB of the uncached DMA arena (command list 1 KB, received-FIS area 256 bytes, command table 2 KB, bounce buffer 512 bytes, plus alignment). The default RawBuffer[65536] in AHCI_DMA_RESOURCES holds 15 ports safely. For 16 or more ports, enlarge it to at least (MAX_SUPPORTED_PORTS + 1) * 4096 bytes (the extra 4 KB covers alignment), for example UCHAR RawBuffer[(MAX_SUPPORTED_PORTS + 1) * 4096];. The driver does not check this at run time: too small an arena overruns the uncached extension.
ABAR range – the driver maps, and on NT 3.x/4.0 claims, only the registers it uses: 100h + 80h * MAX_SUPPORTED_PORTS bytes (500h by default; 1100h for 32 ports). HBAs are often only 4 KB apart, so a fixed larger range would collide with the next controller's ABAR and ScsiPort would reject that controller.
Initiator ID – ScsiPort reserves one target ID for the HBA itself and does not scan it. AhciFindAdapter sets ConfigInfo->InitiatorBusId[0] to MAX_SUPPORTED_PORTS, one past the last port, so it follows the limit automatically and never hides a port.
Device extension – HW_DEVICE_EXTENSION grows by about 550 bytes per port (the Ports[] array, including a 512-byte copy of IDENTIFY data). This is ordinary non-paged memory and not a practical concern.
Uncached memory – a larger arena means a larger physically contiguous ScsiPortGetUncachedExtension allocation per controller (128 KB + 4 KB for 32 ports). This is usually fine on NT and 2000/XP; on Windows 9x with little RAM a large contiguous allocation can fail, and HwFindAdapter then returns SP_RETURN_ERROR.
OS limits – ConfigInfo->MaximumNumberOfTargets is set from MAX_SUPPORTED_PORTS. Values above 8 have not been tested on the 9x and NT 3.5x/4.0 targets; check that the OS's ScsiPort scans that many targets per bus.

AHCI_MAX_CONTROLLERS sizes the table that records which PCI bus:slot each driver instance has claimed, so that two instances never drive the same HBA. Each entry is 12 bytes; raising it costs nothing measurable. If there are more AHCI controllers than entries, the extra controllers are not recorded, and the PCI-scan fallback in AhciFindAdapter may then hand an already-driven HBA to a second instance, so keep this value at or above the number of AHCI controllers in the machine. A checked or DEBUG=1 build logs ClaimDevice: table full when this happens.

After changing either value, rebuild every target you ship (src\9X, src\NT, src\2KXP); they all compile the same ahcint.h.

Debugging

The NT, 2000/XP and x64 variants log via DbgPrint (through the AHCI_DBG macro), visible through a kernel debugger (e.g. WinDbg / i386kd, depending on target OS) or DebugView once a debugger port is attached. Debug output is prefixed [AHCINT].

The 9X variant prints through the VMM's _Debug_Printf_Service (the same approach as SweetLow's nvme9x), so messages are fully formatted and go wherever Windows 9x debug output goes: WDEB386 on a serial port, SoftICE, or DebugView for Windows 9x. The calls are only compiled into DEBUG=1 builds (set DEBUG=1 before build.bat); release builds carry no debug code. Messages are prefixed [ahcint9x].

In code, all targets use one macro with double parentheses (no variadic macros needed for VC++ 2.0 / MSVC 4.0):

AHCI_DBG((AHCI_PFX "Port %lu: TFD=%08lX\n", port, tfd));

Technical Notes

I/O Model

All targets (Fast Polling): every command, ATA or ATAPI, is issued from HwStartIo and polled every 10 µs on PxCI/PxIS/PxTFD (see Command timeout), then completed before HwStartIo returns. PxIE stays 0, so completion never depends on an interrupt being delivered — this also covers text-mode Setup, where the HAL has not assigned an IRQ. The loop exits as soon as PxIS/PxTFD report an error, so an empty CD tray answers NOT READY at once; the port is then stopped and restarted as the AHCI spec requires.

ATA command selection

AhciParseIdentify reads IDENTIFY DEVICE once per disk. 48-bit addressing is used only when word 83 is valid (bits 15:14 = 01), has bit 10 (48-bit Address feature set) set, and words 100–103 hold a capacity — the same rule as Linux's ata_id_has_lba48(). Capacity then comes from words 100–103, otherwise from words 60–61.

Each read/write is checked against that capacity (out of range → CHECK CONDITION, ILLEGAL REQUEST / LBA OUT OF RANGE) and sent as READ/WRITE DMA (28-bit) when it ends below LBA 2^28 and moves at most 256 sectors; only otherwise, and only on a 48-bit device, as READ/WRITE DMA EXT. A zero transfer length in READ/WRITE(10)/(16) completes without touching the disk (ATA would read a count of 0 as 256 / 65536 sectors).

LBAs are kept as two ULONGs (AHCI_LBA), so no __int64 arithmetic — and none of the _aulldiv/_allshl CRT helpers the 9x build does not link — is needed.

Logical sector size

ATA disks may use logical sectors larger than 512 bytes ("4Kn" drives use 4096). AhciParseIdentify reads word 106: when it is valid (bits 15:14 = 01) and bit 12 is set, words 117–118 give the logical sector size in words. 512, 1024, 2048 and 4096 bytes are taken; anything else leaves the port unusable instead of guessing. All ATA LBAs and sector counts are in logical sectors, so the SATL only has to report the right block length (READ CAPACITY(10)/(16), MODE SENSE block descriptor) and size each transfer as count × sector size. When bit 13 is set, bits 3:0 (logical sectors per physical sector) go into READ CAPACITY(16) byte 13, so 512e drives report their 4 KB physical sectors.

What the operating system does with such a disk is up to its class and file system drivers. Tested with QEMU patched to emulate ATA disks with large logical sectors (see TESTS.TXT):

OS	1024 bytes	2048 bytes	4096 bytes
Windows NT 3.1	FAT, NTFS	NTFS (FAT formats but does not mount)	NTFS (FAT formats but does not mount; NT 3.1's FORMAT.COM faults at the end of an NTFS format, the volume is fine)
Windows NT 4.0 SP6	FAT, NTFS	FAT, NTFS	FAT, NTFS
Windows 2000	FAT, NTFS	FAT, NTFS	FAT, NTFS
Windows 95	FAT	FAT	Not usable: Windows 95 reads the MBR and boot sector, then fails every access to the drive ("General failure") without sending a read

Windows 9x specifics

ABAR mapping: ScsiPortGetDeviceBase can fail to return a usable linear address for a memory-mapped PCI BAR on Windows 95 (Microsoft KB Q169584). The 9X build maps the ABAR with the VMM's _MapPhysToLinear service instead, as non-cached (MPL_NonCached), so register polling always sees live hardware state.
HwAdapterState: SCSIPORT.PDR calls this for PCI miniports during Plug and Play state changes; the 9X build provides it (a no-op that returns TRUE), because leaving it NULL makes SCSIPORT.PDR report "Init Failure" for the miniport.
PCI discovery: like the NT targets, the bus:slot SCSIPORT.PDR hands in is tried first, then the PCI bus-scan fallback.

Windows NT 3.1 specifics

NT 3.1's ScsiPort and HAL predate PCI support in non-PnP miniports. The NT build handles this at run time, so the same ahcint.sys runs on NT 3.1, 3.50, 3.51 and 4.0:

HW_INITIALIZATION_DATA size: NT 3.1's ScsiPortInitialize accepts only its own 40h-byte structure and fails anything else before calling HwFindAdapter. DriverEntry first calls it with the NT 3.50–4.0 size on PCIBus; if that fails without HwFindAdapter ever being called, it retries with the 40h-byte layout on the ISA bus.
PCI configuration space: NT 3.1's HalGetBusData only knows CMOS and EISA data, so ScsiPortGetBusData(PCIConfiguration) returns nothing. The driver then uses configuration mechanism #1 (ports CF8h/CFCh) for the bus scan. ScsiPortSetBusDataByOffset does not exist on NT 3.1, so on the whole NT build the PCI command register is written through the same ports, and only when the BIOS left memory space or bus mastering off.
PORT_CONFIGURATION_INFORMATION: 58h bytes on NT 3.1, without SlotNumber and MaximumNumberOfTargets (the access ranges follow right after it). The driver checks ConfigInfo->Length before touching those fields.
DMA: NT 3.1's HAL gives an ISA bus master map registers below 16 MB in every case (it ignores Dma32BitAddresses), so with more RAM every transfer is bounced, and the copy-back overwrites the data the SATL itself writes into the request (INQUIRY, READ CAPACITY, ...): scsidisk sees garbage and the boot ends in 0x7B. Before taking the uncached extension the driver therefore reports Eisa as the interface type; the HAL gives a scatter/gather master on EISA no map registers, and the HBA sees real physical addresses. Tested up to 3 GB RAM.
Interrupt: on the ISA bus a PCI INTx line means nothing, so no interrupt is reported (level 0) and ScsiPort connects none — Fast Polling does not need one.
Several controllers: each HBA asks to be called again (*Again = TRUE); the next call scans for the next unclaimed HBA.

Windows 2000/XP/x64 specifics

Text-mode setup (F6): the setup kernel boots with a bare AHCINT service key; the [Config.scsi.AHCINT] values of txtsetup.oem are written only to the installed system. Without Parameters\PnpInterface\5, the XP x64 / Server 2003 x64 ScsiPort fails IRP_MN_START_DEVICE before HwFindAdapter is called, so setup stops with STOP 0x7B (the x86 ScsiPort tolerates the missing value). DriverEntry therefore creates Parameters\PnpInterface\5 = 1 under its service key when the PnpInterface key does not exist yet, before ScsiPortInitialize. An existing key is left as it is. Both F6 txtsetup.oem files also set the value in [Config.scsi.AHCINT], so a system installed through F6 gets it from setup as well.

Command timeout

A command is polled until the SRB's TimeOutValue minus one second (10 s when the SRB carries none, at most 60 s); commands the driver issues on its own (ATAPI REQUEST SENSE, MODE SENSE translation) get 3 s. Earlier builds used a fixed 3 s for everything, which was wrong both ways:

Too short: one write can legitimately take several seconds — disk spin-up, a dynamically expanding VHD growing under a benchmark's large test file, host cache flushes in a VM. The driver then gave up, stopped the port while the HBA was still transferring and failed the request, so long runs such as CrystalDiskMark could not finish (in QEMU the emulator itself crashed on the mid-transfer stop). Disk class drivers use a 10 s TimeOutValue, so a write now has 9 s.
Too long for short SRBs: ScsiPort runs its own one-second request timer. On a multiprocessor system that timer fires on another CPU while HwStartIo is still polling; if the poll outlasts the SRB's TimeOutValue, ScsiPort starts its own timeout handling (bus reset) for a request the miniport is about to complete. Ending the poll one second early keeps the miniport's timeout ahead of ScsiPort's.

When a command does time out, the port restart issues a COMRESET if the command engine will not stop or the device still reports BSY/DRQ, and sets PxCMD.ST again only after BSY/DRQ have cleared (AHCI 1.3, 10.4.2 and 10.3.1).

One source tree

src\ahcimain.c, src\ahcisatl.c and src\ahcint.h build every target. The build files set the target:

Define	Target	What it changes
`AHCI_W9X`	Windows 95/98/Me	ABAR mapped with VMM `_MapPhysToLinear` (KB Q169584); `HwAdapterState`; debug output via VMM `_Debug_Printf_Service`; implies `AHCI_NT4`
`AHCI_NT4`	NT 3.1/3.50/3.51/4.0 (and 9x)	No HBA reset (links taken over as the BIOS left them); ATAPI packets always carry the DMA bit; no `Dma64BitAddresses` in `PORT_CONFIGURATION_INFORMATION`; access range and INTx reported to ScsiPort by the miniport; no auto-sense (the class driver issues REQUEST SENSE)
`AHCI_NT31_COMPAT`	NT build only (set by `ahcint.h` for `AHCI_NT4` without `AHCI_W9X`)	Windows NT 3.1 support in the same binary, see Windows NT 3.1 specifics
none	2000/XP/2003 x86 and x64	HBA reset (`GHC.HR`) at init; 64-bit DMA when `CAP.S64A`; PnP-assigned interrupt; auto-sense

The 2000/XP x86 and XP x64/Server 2003 x64 drivers differ only in the build environment; there are no architecture-specific code paths.

Memory Allocation

DMA arena – 64 KB (RawBuffer), shared across all ports for command lists, FIS receive buffers, command tables, and bounce buffers; 4 KB per port, enough for 15 ports (see Build-time limits)
PRDT – up to 64 entries per command; ScsiPort is told 32 physical breaks and 128 KB per I/O, so an unaligned 128 KB buffer (33 pages) still fits
Bounce buffer – 512 bytes per port in the DMA arena, used for IDENTIFY and for the ATAPI REQUEST SENSE / MODE SENSE commands the driver issues itself

License

USE AT YOUR OWN RISK. This driver talks directly to storage controller hardware on operating systems no longer supported or patched by Microsoft. Not recommended for any system holding data you can't afford to lose.

Acknowledgments

The AHCI 1.x and ATA/ATAPI-8 specifications
Windows 95 DDK and Windows NT4/2000/XP DDK documentation

Special Thanks

infuscomus for porting driver to x64
Dietmar for Fast Polling idea
DominBear for nvme2k project
SweetLow for nvme9x (Windows 9x VMM debug output and _MapPhysToLinear technique)
UniATA project
Windows 2000 Dev Community
Testers
And everyone which supports it

Name		Name	Last commit message	Last commit date
bin		bin
src		src
.gitattributes		.gitattributes
LICENSE		LICENSE
README.md		README.md
TESTS.TXT		TESTS.TXT

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