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z486MEGA65 v0.1-preview

z486MEGA65 v0.1-preview Pre-release
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@TiwazM TiwazM released this 04 Nov 00:21
v0.1-preview
849fc65

The first preview of z486, nand2mario's 486DX2-class PC from z486_MiSTer, on the MEGA65 R6.

It boots DOS and Windows 3.11 and runs games from the CD era. This is a preview, so expect some rough edges.

Features

PC

  • z486 486DX2-class CPU at 64 MHz, with L1 caches and an x87 FPU
  • 256 KB L2 cache in block RAM, as on a 486 board
  • 64 MB RAM (the R6's SDRAM)
  • Turbo switch: CAPS LOCK slows the CPU to 33 MHz for games that run too fast

Video

  • Tseng ET4000 SVGA, up to 1024x768 in 256 colours (Windows 3.11 included)
  • HDMI out at 720p, 480p, 800x600, 1024x768, 1280x1024, or the PC's own native resolution
  • Scaling filters (Sharp, Smooth, Pixels) and optional scanlines (25 % or 50 %)
  • No tearing when the PC's 70 Hz text mode goes out at 60 Hz

Sound

  • Sound Blaster 16 with OPL3 FM music
  • CD audio, played in hardware and mixed through the Sound Blaster's CD volume

Disks

  • IDE hard disk from an image file on the SD card
  • Floppy drives A: and B: from image files, swapped from the menu
  • ATAPI CD-ROM drive:
    • ISO images, raw BIN images, and BIN/CUE discs, including multiple files, WAVE audio, pregaps and mixed sector sizes
    • Up to 99 tracks, with CD audio
    • Works with DOS CD-ROM drivers and MSCDEX, and Windows' Media Player
  • Disc and disk images mount automatically at start-up, or from the menu at any time

Input

  • The MEGA65 keyboard as a PC keyboard, with symbols as on the keycaps. MEGA works as an Fn key for Page Up/Down, Home/End and Delete.
  • PS/2 mouse on joystick port 1:
    • Commodore 1351, or a mouSTer in C64 mode: both buttons, detected automatically
    • Amiga mouse, or a mouSTer in Amiga mode: F13 is the right button
    • z486_MiSTer's system BIOS gets a sync check for the mouse as it loads, so the pointer can't get stuck jumping between the screen edges
  • Game port joystick on port 2 with up to three buttons. The second fire button can be on pin 9 (C64GS style) or pin 5, set in the menu.

Core

  • Menu on HELP: disks, HDMI mode, filter, scanlines, joystick, reset; settings are saved to the SD card
  • The reset button and Ctrl+Alt+Del restart the PC cleanly

Tested

On an R6: MS-DOS, FreeDOS, Windows 3.11 (SVGA, Media Player CD audio), DOOM, SimCity 2000, Wing Commander III, King's Quest VI, Phantasmagoria, The 7th Guest, Ultima Underworld 1 and 2, Day of the Tentacle (CD talkie), The Secret of Monkey Island (CD, with its CD music), and Quake (slowly: about 6 fps in timedemo demo1).

Tips:

  • Ultima Underworld 2: SET BLASTER=A220 I5 D1 T4 before it starts, and its Sound Blaster Pro option. With its Sound Blaster option it hangs.
  • Wing Commander III: start it without EMM386 (HIMEM.SYS only). With EMM386, a video can hang the game on a black screen.
  • TIE Fighter finds the joystick when the stick is held to the upper left while it starts (as on ao486 on MiSTer).

Getting started

  1. Copy z486-R6-v0.1-preview.cor to the SD card and flash it with MEGAFLASH. It shows as "z486", version v0.1-preview. The .bit is the same core, for loading over JTAG.
  2. Put the BIOS files on the SD card. They're not included here: they come with z486_MiSTer in verilator/, the same files MiSTer users put in games/Z486.
/z486/boot0.rom    the system BIOS (required)
/z486/boot1.rom    the VGA BIOS (required)
/z486/hdd.img      optional: the hard disk at start-up (a raw disk image)
/z486/cdrom.cue    optional: the CD-ROM's disc at start-up (its files in /z486)
/z486/cdrom.iso    optional: the same as an ISO image
/z486/floppy.img   optional: drive A: at start-up
  1. Press HELP for the menu, to mount images and pick the HDMI mode.

Known limits

  • A 486 at 64 MHz with a microcoded FPU: Pentium-era 3D games are slow.
  • No scroll wheel. With an Amiga mouse, the right button is F13: the MEGA65 can't read pin 9.
  • Some games don't detect the joystick.
  • HDMI runs at 60 Hz while the PC draws at 70 Hz, so fast animation can judder (King's Quest VI's intro).
  • With a system BIOS other than z486_MiSTer's boot0.rom, the mouse pointer can get stuck jumping between the screen edges: load the mouse driver again (ctmouse).
  • The MEGA65's own floppy drive isn't used.
  • CD music while a game loads from the hard disk hasn't been tried on the board yet.
  • After flashing this version, the menu settings return to their defaults once.

Credits

  • z486 and z486_MiSTer by nand2mario. z486_MiSTer's chipset builds on ao486 by Aleksander Osman and its MiSTer port by Alexey Melnikov.
  • MiSTer2MEGA65 by sy2002 and MJoergen; Megamiga's fork and pc10-iii by Johan Smolinski.
  • PCXT-EGA-MEGA65 by silent-command.

The bitstream contains z486's recovered CPU microcode, which is not covered by z486's Apache licence (see z486's LICENSE-SCOPE.md).

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