PCXT_MiSTer/README.md

IBM PC/XT for MiSTer FPGA

PCXT port for MiSTer by @spark2k06.

Discussion and evolution of the core in the following misterfpga forum section:

https://misterfpga.org/viewforum.php?f=40

Description

The purpose of this core is to implement a PCXT as reliable as possible. For this purpose, the MCL86 core from @MicroCoreLabs and KFPC-XT from @kitune-san are used.

The Graphics Gremlin project from TubeTimeUS (@schlae) has also been integrated in this first stage.

JTOPL by Jose Tejada (@jotego) was integrated for AdLib sound.

Key features

• 8088 CPU with these speed settings: 4.77 MHz, 7.16 MHz, 9.54 MHz cycle accurate, and PC/AT 286 at 3.5MHz equivalent (max. speed)
• Support for IBM PCXT 5160 and clones (CGA graphics)
• Main memory 640Kb + 384Kb UMB memory
• Simulated Composite Video (CGA)
• Simultaneous video Hercules Graphics Card, F11 -> Swap Video Output with CGA
• Enable/Disable of CGA and Hercules I/O ports
• 1st Graphics Card selection from System & BIOS
• EMS memory up to 2Mb
• XTIDE support
• Audio: Adlib, C/MS & speaker
• Joystick support
• Mouse support into COM1 serial port, this works like any Microsoft mouse... you just need a driver to configure it, like CTMOUSE 1.9 (available into hdd folder)
• 2nd SD card support

Build configuration (config.tcl)

The default configuration focuses on broad PC/XT compatibility:

• System/ROM set to PCXT
• CGA + HGC enabled for widest video support
• OPL2 enabled for common DOS FM audio
• CMS enabled
• EMS + A000 UMB enabled for expanded memory
• Tandy-specific video/audio/keyboard by default

This default maximizes software compatibility while keeping the feature set coherent for a PC/XT target. You can edit config.tcl to enable or disable any macro and rebuild for a different profile.

Resource profile

Video options dominate resource usage. CGA uses 282/553 RAM blocks and HGC/MDA uses 270/553, so the default PCXT profile (CGA+HGC) is heavier than either single video build. Enabling all features reaches 553/553. The device budget is 553 RAM blocks and 5,662,720 block memory bits.

Columns are separate builds: Base (all features off), single-feature builds, CGA+TandyVideo (CGA + Tandy video, included for comparison), and All (everything enabled). Values are from recent synthesis runs and can be regenerated by rebuilding with different config.tcl settings.

Resource	Max	Base	CGA	CGA+TandyVideo	HGC/MDA	TandyAudio	TandyKBD	OPL2	CMS	EMS	A000_UMB	All
ALMs	110,000	12,551	14,229	14,442	13,546	12,802	12,549	13,266	13,505	12,599	12,648	17,605
Registers	~220,000	17,861	19,755	20,081	19,680	17,974	17,883	18,509	18,815	17,776	17,739	24,311
Block memory bits	5,662,720	945,035	2,124,705	3,042,209	2,026,404	945,035	945,035	952,077	945,035	945,035	945,035	4,313,183
RAM blocks (M10K)	553	138	282	394	270	138	138	147	138	138	138	553
DSP blocks	112	33	35	35	33	33	33	34	37	33	33	40

Default configuration (current config.tcl and output_files/PCXT.fit.summary) resource usage, shown as percent of the Max column above:

Resource	Used	% of Max
ALMs	17,111	15.6%
Registers	23,913	10.9%
Block memory bits	3,397,414	60.0%
RAM blocks (M10K)	449	81.2%
DSP blocks	40	35.7%

Quick Start

• Copy the contents of games/PCXT to your MiSTer SD Card and uncompress hd_image.zip. It contains a FreeDOS image ( http://www.freedos.org/ )
• Select the core from Computers/PCXT.
• Press WinKey + F12 on your keyboard.
  • Model: IBM PCXT.
  • CPU Speed: PC/AT 3.5MHz (Max speed)
  • FDD & HDD -> HDD Image: FreeDOS_HD.img
  • BIOS -> PCXT BIOS: pcxt_micro8088.rom
• Choose Reset & apply settings.

ROM Instructions

ROMs should be provided initially from the BIOS section of the OSD menu. The core has a single BIOS slot; on subsequent boots it is not necessary to provide them unless you want to use others. Original and copyrighted ROMs can be generated on the fly using the python scripts available in the SW folder of this repository:

• make_rom_with_ibm5160.py: A valid ROM is created for the PCXT core (pcxt.rom) based on the original IBM 5160 ROM, requires the XTIDE BIOS at address EC00h to work with HD images.
• make_rom_with_jukost.py: A valid ROM is created for the PCXT core (pcxt.rom) based on the original Juko ST ROM, and with the XTIDE BIOS embedded at address F000h.

From the same BIOS section of the OSD it is possible to specify an XTIDE ROM of up to 16Kb to work at address EC00h. It is also provided in this repository.

Other Open Source ROMs are available in the same folder:

• pcxt_pcxt31.rom: This ROM already has the XTIDE BIOS embedded at address F000h. (Source Code)
• pcxt_micro8088.rom: This ROM already has the XTIDE BIOS embedded at address F000h. (Source Code)
• ide_xtl.rom: This ROM corresponds to the XTIDE BIOS, it must be maintained for some scripts to work, it can also be upgraded to a newer version. (Source Code)

Note: Not all ROMs work with MDA video: (IBM5160, Yuko ST and pcxt31 works)

Other BIOSes

• https://github.com/640-KB/GLaBIOS

Mounting the FDD image

The floppy disk image size must be compatible with the BIOS, for example:

• On IBM 5160 only 360Kb images work well.
• On Micro8088 only 720Kb and 1.44Mb images work properly.
• Other BIOS may not be compatible, such as OpenXT by Ja'akov Miles and Jon Petroski.

It is possible to use images smaller than the size supported by the BIOS, but only pre-formatted images, as it will not be possible to format them from MS-Dos.

Developers

Any contribution and pull request, please carry it out on the prerelease branch. Periodically they will be reviewed, moved and merged into the main branch, together with the corresponding release.

Thank you!