Permission is granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to use, compile, modify, and make derivative works of the Software for non-commercial purposes only, subject to the following conditions:

1. The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
2. The Software may not be sold, offered for sale, licensed for a fee, or used in any commercial product or service without explicit prior written permission from the copyright holder.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND

commercial purposes please contact me.

currently undergoing a complete refactor, refer to discussions for context.

Currently being refactored, refer to discussions

A clean-room C implementation of the Amstrad PC1640 BIOS with hopefully same behavior.

Implementation notes

• The BIOS uses GNU-style IA-16 inline assembly where real 8086 instructions are required: reset entry, interrupt wrappers, port I/O, and boot transfer.
• Machine state that genuinely lives in RAM still has software mirrors in the BDA/private work area.

Layout

• src/ BIOS implementation modules (PIC, PIT, keyboard, video, floppy, IDE, etc).
• config/ ELKS-style Kconfig build system (Configure, Menuconfig, lxdialog).
• config.in Master configuration description (like Linux kernel Kconfig).
• scripts/ Build helpers (mkconfig.sh translates .config to C header + make fragment).
• tools/ ROM image tools, 86Box test harnesses, string extraction.
• build/ Output artifacts (ELF, ROM images, chip files).

Prerequisites

• ia16-elf-gcc cross compiler (expected at ~/somewhere). i recommend downloading elks and using elks toolchain as that is what i use.
• nasm assembler.
• python3 (for ROM image tools and Exomizer bootstrap only).i am going to drop the python code. was good for prototyping
• ncurses development headers (for make menuconfig).
• GNU make.

Quick start

make defconfig          # Generate default .config (stock PC1640 profile)
make                    # Build ROM image, chip files, and selftest image

Configuration

The build system uses an ELKS/Linux kernel-style Kconfig menu system. Configuration is stored in .config and translated into build/config_autogen.h (C defines) and build/config.mk (make variables) by scripts/mkconfig.sh.

make defconfig          # Restore stock PC1640 defaults
make config             # Text-mode line-by-line configuration
make menuconfig         # Interactive ncurses menu configuration

After running any configuration command, simply make to rebuild with the new settings. The build system automatically detects .config changes and regenerates the header and make fragment.

Configuration sections

Section	Key options
Machine Identity	Brand name, website, ROS release/issue numbers
Hardware	Base memory, Paradise PEGA1A, Amstrad mouse, RTC, math coprocessor
Peripheral Ports	COM1/COM2/LPT1/LPT2 I/O base addresses
Video	Fallback video equipment, text attribute, PC1640 switch block options
Option ROMs	Video and non-video option ROM scanning
Floppy Disk	Controller enable, drive types (360K/720K), INT 13h AH=08 compat
IDE Hard Disk (XTIDE)	XTIDE enable, I/O base, LBA translation, EDD extensions
RTC Defaults	Default date/time when battery is dead
POST Options	Pretty wait panel, Space Invaders sound effect
Debug	Port E9, COM1 debug output, video state tracing

Build targets

Run make help for a complete list. Key targets:

Configuration:
  defconfig      - Generate default .config
  config         - Text-mode configuration (like Linux "make config")
  menuconfig     - Ncurses menu configuration (like Linux "make menuconfig")

Build:
  all            - Build ROM image, chip files, and selftest (default)
  clean          - Remove build directory
  mrproper       - Remove build directory and .config

Testing (requires 86Box):
  86box-build    - Build 86Box debug version
  86box-run      - Run BIOS in 86Box with floppy image
  86box-selftest - Run self-test in headless 86Box
  86box-ide-smoke - Run IDE smoke test in 86Box

Build outputs

File	Description
build/bios.bin	16 KiB ROM image (compressed payload + decompressor stub)
build/bios.elf	ELF with debug symbols
build/bios.map	Linker map file
build/40044.v3	Even chip file (with mirror)
build/40043.v3	Odd chip file (with mirror)

The ROM is built in stages:

1. Compile all C sources to a single ELF
2. Extract raw binary payload (up to 32 KiB)
3. Compress with Exomizer (-P47) higher values seem to crash the decruncher. will look into that
4. Assemble NASM decompressor stub
5. Pack into 16 KiB ROM image with reset vector
6. Split into interleaved even/odd chip files

IDE support

Built-in XTIDE-compatible IDE driver provides INT 13h services for ATA hard drives connected via an 8-bit ISA IDE controller. Supports:

• Legacy CHS addressing
• LBA28 with translated CHS geometry
• INT 13h extensions (EDD) for direct LBA access
• Boot from IDE when floppy boot fails (configurable)

The IDE driver is compatible with XTIDE ISA adapters using the standard 8-bit data transfer protocol

**note at the moment due to optimization reasons, you can either have floppy or ide, not both, sorry!

PCem usage

Built ROMs install directly as build/40043.v3 and build/40044.v3. For local debugging, copy those ROMs into ~/.pcem/roms/pc1640/.

Default test media

• The stock 360 KiB smoke path uses test_media/ibm_dos_330_disk1_360k.img.
• The companion second disk is available as test_media/ibm_dos_330_disk2_360k.img.

Technical notes

• The ROM is linked as a 16 KiB in-socket image; the motherboard maps it at physical 0xFC000..0xFFFFF.
• Reset vector placement: linker script places .reset at image offset 0x3FF0, which corresponds to physical 0xFFFF0.
• Port I/O: src/io.c and src/bios_hw.h drive the XT/PC1640 ports directly with GNU-style inline assembly.
• Strings: tools/extract_strings.py regenerates src/bios_strings.inc from the original decompiled ROM so the clean BIOS source keeps the original text corpus.