Atari ST/STe and Falcon030 for MEGA65 (MegaST)

This is a port of the AtariST_MiSTer core (the "MiSTery" Atari ST/STe core by Till Harbaum, Gyorgy Szombathelyi, Jorge Cwik, Alexey Melnikov and others) to the MEGA65, using the MiSTer2MEGA65 framework.

Since 1.1.6 MegaST also contains an Atari Falcon030 (test version, R6 only). The MEGA65 version was engineered for MegaST: the SDRAM memory controller, the 68882 FPU on a RISC-V CPU inside the FPGA, the MEGA65 integration, the menu, machine switching and TOS handling, and many fixes. Its CPU and chipset come from the open-source Falcon_MiSTer and AP68030 projects.

MEGA65 port by Chris Freeman (@freemchr).

Status: the ST/STe is stable and running on real hardware; the Falcon030 is a test version. MegaST is developed and tested on a MEGA65 R6 and runs games and GEM programs from floppy and hard disk images; the Falcon030 boots EmuTOS, TOS 4.04 and FreeMiNT and runs several Falcon demos. Download the core from Releases; see below for what has been tested on the MEGA65. Please report problems and successes in the issues.

Latest version: 1.5 (November 4, 2026): on the Falcon, EmuTOS with "Hard disks on SCSI" now also works with slow SD cards (installing and copying no longer stop with "Your output device is not receiving data"); see VERSIONS.md. 1.4 (November 2, 2026) brought the first, too short, fix for this. VERSIONS.md. 1.3 (November 1, 2026): Space on the "TOS:" line removes a chosen TOS; for the Falcon a faster turbo with the caches off, cartridges refused cleanly, and FASTRAM.PRG (extras/ in the zip) gives TOS 4.04 the Fast RAM. 1.2 (October 27, 2026) brought the menu look in the style of the Atari GEM desktop, the Falcon option "Hard disks on SCSI" and a ready IDE hard disk image. 1.1.6 (October 25, 2026) added the Atari Falcon030 (test, R6 only), see New in 1.1.6 below. Updating from a version older than 1.1.6: copy the new atarist/fccfg and atarist/fcmount from the zip, otherwise the menu settings are not saved. 1.1.5 made the Viking 1280x1024 card work, shown sharp at 1:1 on HDMI. Since 1.1 (October 16, 2026) the MEGA65's internal floppy drive works as the ST's drive A: (read only, issue #15, see Real floppy drive). Core files for the R3/R3A and R6 (from 1.1.4 on there are no separate R4 and R5 files; if you have one of these boards, please open an issue). All versions up to 0.4.10 damage hard disk images when writing (issue #11): if you wrote to an image with one of them, restore it from a backup.

New in 1.1.6: the Atari Falcon030

MegaST is now an Atari ST/STe and an Atari Falcon030. Choose the machine in the menu (Help → "Machine" → "Falcon030"). The Falcon is a test version and needs the SDRAM of the R6 (the R3/R3A core stays an ST). It runs EmuTOS and Atari's TOS 4.04, Falcon demos and programs, and boots FreeMiNT from an IDE hard disk image. Details in Falcon030 (test); please report what works and what does not in the issues.

The menu is split per machine. Every machine has its own settings page, and things that belong together are grouped:

 MegaST
 <floppy, hard disk, TOS and cartridge lines>
 Machine                 >   Atari ST, Atari STe, Mega STe, STEroids, Falcon030
 ST/STe settings         >   memory, blitter, mono monitor, borders, Viking card, stereo YM
 Falcon030 settings      >   monitor (VGA/RGB/TV/mono), CPU 32 MHz, 4 MB ST-RAM, Fast RAM
 Drives & images         >   write protection, floppy swap, real floppy drive, remembering images
 Controllers & ports     >   mice, joysticks, joypads, PMOD ports, Cubase dongles, keyboard
 HDMI / VGA              >   video modes, scanlines, 15 kHz
 CRT emulation, Zoom-in, Audio improvements
 Reset                       resets the machine that runs (was "Reset Atari ST")

How the TOS works with two machines. The ST and the Falcon need different TOS versions, so each machine has its own:

	Atari ST / STe	Falcon030
Loaded at power on and after switching to it	atarist/tos.img	atarist/tosfalc.img
In the zip	EmuTOS (256 KB)	EmuTOS for the Falcon (512 KB)
TOS it can run	192 KB (1.00–1.04) or 256 KB (1.06–2.06), EmuTOS	512 KB (TOS 4.0x), EmuTOS 512 KB
A TOS chosen with "TOS:"	remembered for the ST	remembered for the Falcon

• Choosing a TOS with "TOS:" loads it for the machine that runs and restarts it. With fcmount on the SD card it is remembered for that machine and comes back at the next power on.
• Switching the machine (ST ↔ Falcon030) closes the menu, loads the new machine's TOS (the one remembered for it, otherwise its .img file from the table) and starts it. Switching back gives the old machine its own TOS again: for example ST with TOS 2.06 → Falcon with TOS 4.04 → ST with TOS 2.06.
• A TOS the machine cannot run is refused with a message, and the file browser stays open: a 512 KB TOS on the ST, or an ST TOS on the Falcon.
• To go back to the .img file of the table, select the "TOS:" line and press Space: the chosen TOS is removed and forgotten, the menu closes and the machine restarts with tos.img (ST) or tosfalc.img (Falcon). Choosing that file with "TOS:" does the same. With "Remember TOS/cartridge" off ("Drives & images") the machines always start with these files.

New settings files. The menu is larger, so 1.1.6 keeps the settings in atarist/fccfg (119 bytes) and the remembered images in atarist/fcmount (1792 bytes). Copy both from the zip (and tosfalc.img and fcnvram for the Falcon). The old stcfg and stmount are no longer read; leave them on the card, so going back to 1.1.5 keeps its settings.

Support: MegaST is free and open source. If you enjoy it, you can support its development via Buy Me a Coffee or GitHub Sponsors.

Tested on a MEGA65 R6

Area	Result
TOS 1.04, boot to the desktop	works
TOS 2.06 (STe) and EmuTOS 1.4, boot and hard disk	work (tester reports)
TOS 1.62 (STe, 1 MB)	works (tester report, issue #21)
TOS 1.00, 1.02, 1.06	boot to the desktop in simulation, not tried on hardware yet
Floppy disks: loading, changing disks, reset with a disk inserted, saving	works
Hard disk: 4 GB .vhd image (MiSTer image), boot, reading files, launching programs	works
Hard disk: writing files	broken up to 0.4.10, works since 0.4.11 (tester report, issue #11)
Remembered disk images restored at power-on	broken in 0.4.12/0.4.13, works since 0.4.14 (tester reports, issues #11, #12)
MEGA65 keyboard, all keys (A fixed in 0.4.7), numeric keypad via MEGA	works
Atari ST mouse, in port 1 or port 2	works; right button as a short click only (see Usage, issue #17)
Amiga mouse (optical, incl. right button), in port 1 or port 2	works
mouSTer USB adapter, firmware 3.23.5313, Amiga or 1351 mode (see Usage)	works (tester report, issue #17)
Joystick, with debouncing for bouncing and worn switches (Suncom TAC-2)	works
Menu settings saved on the SD card (fccfg)	works
VGA scanlines, full borders	works
HDMI picture centred, not cut off on the right (576p, 720x480, 640x480)	works (since 1.0)
Internal floppy drive as A: (original Jim Power disk: boot, game)	works (since 1.1); R3-R5 not tested with the drive
Internal floppy drive with EmuTOS (drive A: on the desktop)	works since 1.1.1 (no drive icons in 1.1, issue #24); R3-R5 not tested with the drive
Games: Golden Axe, Great Giana Sisters, Turrican	work
Games: Buggy Boy, Goldrunner, Goldrunner II, The Hitchhiker's Guide to the Galaxy, Lemmings	work (tester report, issue #21)
Viking card with mist_vhi.prg (TOS 1.04/2.06): sharp 1280x1024 desktop on HDMI, MEGA65 menu, switching off	works (since 1.1.5, R6)
Cartridges, PMOD serial/MIDI/printer, Cubase dongles, mono monitor	not tested yet
1351 mouse	works (tester report on the R3, issue #22)
HDMI "DVI mode (no sound)" with a DVI monitor	works (tester report, issue #4)
R3 and R3A boards (CORE-R3.xpr, 512 KB)	work, including hard disk images (tester reports, issues #2, #22)
R4/R5 boards (CORE-R4.xpr, CORE-R5.xpr)	not tested yet

Falcon030 (test, R6):

Area	Result
EmuTOS for the Falcon (tosfalc.img), boot to the desktop	works
Atari TOS 4.04, boot to the desktop	works (since 1.1.6)
Switching ST ↔ Falcon030 in the menu, each machine with its own TOS	works (since 1.1.6)
HDMI picture with "Monitor: VGA (31 kHz)"	works
Falcon demos and programs	several work (tested on the R6)
FreeMiNT 1.19 from an IDE image (HDDRIVER): kernel, drivers, text shell, TOS desktop (GEM=ROM)	works
FreeMiNT with the XaAES desktop	white screen, being worked on
Fast RAM, 32 MHz turbo, real floppy drive, joypads, serial/MIDI, RGB/TV/mono monitor types	not tested yet

Screenshots

TOS 1.04 desktop	EmuTOS 1.4 (included in the release zip)

(Frames from the simulation of the core, i.e. the exact picture the core generates, before the HDMI scaling. Falcon030 screenshots will follow.)

Features

MegaST contains two machines; choose one under "Machine" in the menu.

Atari ST / STe / Mega STe (all boards)

• Atari ST, STe, Mega STe (16 MHz) and "STEroids" modes
• 512 KB, 1 MB, 2 MB, 4 MB, 8 MB and 14 MB of ST RAM (R3/R3A: 512 KB)
• Blitter (always on in STe mode, optional in ST mode)
• All TOS versions: 192k TOS (1.00 - 1.04), 256k TOS (1.06, 1.62, 2.06) and EmuTOS; tos.img is loaded at power on, another TOS image can be loaded from the menu
• Two ACSI hard disks (.hd/.img/.vhd images, read/write, directly on the SD card, up to 4 GB)
• ROM cartridges (raw .img or .stc, up to 128 kB), Cubase 2 and Cubase 3 dongle
• Viking/SM194 compatible 1280x1024 monochrome card (HDMI: 1:1 at 1280x1024, VGA: 640x512 grey scale; not on the R3/R3A)
• Color (low/medium resolution, 50/60 Hz) and monochrome (SM124, 71 Hz or 60 Hz) monitor, normal or full borders (overscan)
• YM2149 (mono or stereo) and STe DMA sound
• Real IKBD (HD6301) with the MEGA65 keyboard mapped directly into the ST keyboard matrix
• Mega ST real time clock (RP5C15), set from the MEGA65's real time clock
• STe enhanced joystick ports (fire button only)

Atari Falcon030 (test version, R6 only, see Falcon030 (test))

• 68030 with caches and PMMU at 16 MHz, or 32 MHz (turbo); 68882 FPU
• VIDEL graphics: ST modes and Falcon modes with 2 to 256 colours and True Color; monitor type VGA, RGB, TV or mono
• DSP56001, DMA sound, sound matrix and YM2149
• 14 MB (or 4 MB) ST-RAM, optionally 48 MB Fast RAM (TT-RAM)
• EmuTOS (tosfalc.img, in the release zip) or Atari TOS 4.0x
• Two IDE hard disks (.hd/.img/.vhd, up to 4 GB); FreeMiNT boots
• Enhanced joystick ports (Jaguar style joypads and paddles), NVRAM saved on the SD card

Both machines

• Each machine has its own TOS, remembered separately (TOS)
• Two floppy drives (.st images, read/write), can be swapped (boot from B:); blank disk images can be created with tools/make_st_disk.py
• The MEGA65's internal 3.5" drive as drive A: (real DD disks, read only)
• The MEGA65 keyboard, with the numeric keypad via the MEGA key and an optional "as printed" layout
• Atari ST mouse, Amiga mouse, Commodore 1351 mouse or mouSTer USB adapter in MEGA65 joystick port 1 or 2 (menu "Controllers & ports"), joystick in the other port
• Serial port (RS232), MIDI and parallel (printer) port on the MEGA65's PMOD headers (the Falcon: serial and MIDI)
• HDMI (720p/576p/480p/600p) and VGA output: 31 kHz (optionally with scanlines) or 15 kHz RGB (optionally with composite sync, e.g. for SCART), zoom-in without the border
• Menu settings and mounted images remembered on the SD card

Requirements

• MEGA65 R3, R3A, R4, R5 or R6 board. On the R4-R6 the ST RAM is in the SDRAM (up to 14 MB). The R3/R3A has no SDRAM, and its HyperRAM is too slow for the ST's cycle exact memory timing, so its own core (MegaST-R3-...cor) keeps the ST RAM in the FPGA's block RAM: 512 KB ST RAM, no Viking card, no STEroids mode and no Falcon030; everything else is the same. The Falcon030 needs the SDRAM (R6; the R4/R5 have it too but are not tested).
• SD card with a folder /atarist containing
  • tos.img: the TOS of the ST (mandatory). The release zip contains the free EmuTOS as tos.img; a TOS ROM dump of your own Atari also works.
  • tosfalc.img: the TOS of the Falcon030 (512 KB; EmuTOS for the Falcon in the release zip, or your own TOS 4.0x), and fcnvram, the Falcon's NVRAM (in the release zip).
  • your floppy disk images (.st), hard disk images (.hd, .img, .vhd) and cartridges (.stc, .img)
  • fccfg, an empty settings file, if you want the menu settings to be saved (in the release zip, or cd M2M/tools && ./make_config.sh fccfg auto). Without it, the menu works but its settings are not saved. The file must have exactly as many bytes as the menu has lines (OPTM_SIZE in CORE/vhdl/config.vhd, currently 119). Up to 1.1.5 the file was stcfg (104 bytes); 1.1.6 does not read it, so copy fccfg from the zip (the settings start from the defaults once).
  • fcmount, if the core shall remember the mounted floppy and hard disk images and the TOS and cartridge chosen in the menu (in the release zip; up to 1.1.5 stmount). It must have exactly 1792 bytes, all 0x00 or all 0xFF (e.g. python3 -c "open('fcmount','wb').write(bytes(1792))").

Usage

• Press Help to open the on-screen menu: mount disks, choose the machine, the video output and more. Every line and setting is explained in The menu below. "Reset" resets the machine that runs (like the reset button of the MEGA65, the RAM is kept).

• With /atarist/fcmount on the SD card (see Requirements), the core remembers the images you mounted and the TOS and cartridge you chose, and loads them again at the next start, before the ST boots (so a hard disk is found and the right TOS starts). To unmount (eject) a drive, select its line in the menu and press Space; this also forgets it. A drive that still has unsaved writes stays mounted until they are written to the SD card (a few seconds). A long press of the reset button restarts the core like a power cycle, so the remembered images come back; unmount them in the menu if you want empty drives. An image that is no longer on the SD card is skipped. In "Drives & images", "Remember floppies" and "Remember TOS/cartridge" (both on by default) decide whether the floppies and the TOS and cartridge come back at the next start; when off, the drives start empty and tos.img is used. Hard disks are always remembered.

• Keyboard mapping (the MEGA65 has a C64 style layout, symbols are mapped by position):

  MEGA65	Atari ST
  F1, F3, F5, F7, F9	F1, F3, F5, F7, F9
  Shift + F1 .. F9	F2, F4, F6, F8, F10
  MEGA + F1 .. F9 (with or without Shift, since 1.0)	Shift + F1 .. F10 (F11 .. F20 in GFA-Basic, STOS)
  F11, Run/Stop	Undo
  F13	Help
  Inst/Del	Backspace
  Arrow up (↑)	Delete
  No Scroll	Insert
  Clr/Home	Clr/Home
  Ctrl, Alt, Esc, Tab	Control, Alternate, Esc, Tab
  Caps Lock	Caps Lock
  + - £	- = \
  @ * ←	[ ] `
  : ; =	; ' ISO key (<>)

• Numeric keypad: hold the MEGA key. MEGA + 0..9, +, -, *, /, . and Return are the keypad keys, MEGA + Shift + 8 / 9 are the keypad keys ( and ).

• Keyboard "as printed" (0.4.8, "Controllers & ports" → "Keyboard", issue #6): digits and symbols give the character printed on the MEGA65 key instead of the ST key at the same position, e.g. Shift + 2 is ", + is +, @ is @, : is :. The ST's own layout depends on the language of the TOS, so choose "As printed, US TOS" or "As printed, UK TOS" (the EmuTOS in the release zip is UK). Other TOS languages: use "ST keys (positional)", the default. Characters that are not printed on the MEGA65:

  MEGA65	Atari ST
  Shift + : / ;	[ / ]
  Shift + @ / *	{ / }
  £, Shift + £	\, |
  Shift + -	_
  ←, Shift + ←	`, ~

  Keys without a shifted symbol on the MEGA65 (0, +, =, ↑) give the same character with Shift.

• Mouse: an Atari ST mouse works out of the box. For an Amiga mouse (or a mouSTer in Amiga mode) or a Commodore 1351 mouse, select it first in the menu: "Controllers & ports" → "Mouse type" → Amiga / 1351. With the wrong mouse type, an Amiga mouse only jitters in small steps. "Mouse port" selects the MEGA65 port the mouse is plugged into (default: port 1); the joystick goes into the other port. The right button is read from pin 9, which has no pull-up on the MEGA65, so an open pin looks like a pressed button. The core therefore ignores the right button until it has seen pin 9 released. An adapter that leaves pin 9 open (or a joystick in the mouse port) gets no right button, but it no longer holds it down.

• Right button of an Atari ST mouse: the Atari mouse does not pull pin 9 up either (on the ST the mainboard does). Its button only grounds the pin, and after a release the open line takes about 10-13 seconds to float back up (measured on an R6; 2-6 seconds on a tester's board). The core can not see the release, so with Mouse type = Atari a right click counts as a short click (200 ms): right-click menus work, but holding the right button (dragging, drawing) does not, and a second right click only counts once the line has floated back up (about 10 seconds later).

• mouSTer (USB mouse adapter): the mouSTer emulates a real mouse so closely that its right button has the same pull-up problem: it sticks after the first click. With mouSTer firmware 3.23.5313 or newer, these two setups work (tester report, issue #17):

  Core "Mouse type"	mouSTer INI
  Amiga	[mouster] mode=auto (or mouse), [mouse] type=amiga, activepotlines=true
  1351	[mouster] mode=mouse, [mouse] type=c1351, activepotlines=false

  With activepotlines=true the mouSTer drives the right button line itself (the same setting the MEGA65 Amiga core needs).

The menu

Help opens and closes the menu. Cursor up/down moves, Return selects or toggles, Space on a drive line ejects the image. A line with > opens a submenu; "Back to main menu" (or Help) leaves it. Settings marked ✓ are on; they are saved in /atarist/fccfg (see Requirements).

Main menu

Line	What it does
TOS:	loads a TOS image for the machine that runs and restarts it (see TOS); Space removes it
Floppy A:, Floppy B:	mounts a .st floppy image
Hard disk 0:, Hard disk 1:	mounts a hard disk image (ACSI on the ST; on the Falcon IDE master/slave, or SCSI ID 0/1 with "Hard disks on SCSI")
Cartridge:	loads a cartridge image (ST/STe only); Space removes it
Machine:	the machine, see below
ST/STe settings, Falcon030 settings, Drives & images, Controllers & ports, HDMI:, VGA:	submenus, see below
HDMI: CRT emulation	a CRT-like picture on HDMI (scaler filter); off by default
Zoom-in (hide border)	shows only the graphics area without the border; off by default
Audio improvements	filters the sound; off by default
Reset	resets the machine that runs (warm reset, the RAM and the mounted images are kept)
About & Help	version and keys

Machine (one of them)

Choice
Atari ST (default), Atari STe, Mega STe (16 MHz), STEroids (turbo)	the ST family; changing between them restarts the ST with a cold boot
Falcon030	the Falcon (test, R6 only). Switching between the ST family and the Falcon closes the menu, loads the TOS of the new machine and starts it

ST/STe settings (only for the ST family)

Setting	Default	What it does
Memory: 512 KB / 1 MB / 2 MB / 4 MB / 8 MB / 14 MB	1 MB	ST RAM; a change restarts the ST (R3/R3A: always 512 KB)
Blitter (Atari ST)	off	the blitter in the Atari ST mode (the STe modes always have it)
Mono monitor (SM124)	off	the monochrome monitor (640x400, 71 Hz) instead of colour
Mono: 60 Hz, not 71 Hz	off	the mono picture at about 60 Hz, for monitors and HDMI (Video)
Full borders (overscan)	off	shows the full border area
Viking 1280x1024 card	off	the Viking/SM194 card; a change resets the ST (Viking/SM194 card)
Stereo YM sound	off	the three YM2149 channels spread over left and right instead of mono

Falcon030 settings (only for the Falcon)

Setting	Default	What it does
Monitor: VGA (31 kHz) / RGB (15 kHz) / TV (15 kHz) / Mono (SM124)	VGA	the monitor the Falcon believes is connected; it decides which video modes TOS and programs offer. The picture goes to HDMI and VGA with every setting, so keep VGA if you use HDMI
CPU at 32 MHz (turbo)	off	the 68030 at 32 MHz instead of 16 MHz: about 1.6 times as fast for programs that use the 68030's caches (GEM, most Falcon software); programs that switch the caches off (many older games and demos) about 1.1 times as fast (since 1.3; before, slightly slower than at 16 MHz). Tools that read the Falcon's bus control register still show 16 MHz (a real Falcon only has 8 and 16 MHz)
ST-RAM 4 MB (not 14 MB)	off	4 MB ST-RAM instead of 14 MB
Fast RAM 48 MB (TT-RAM)	off	48 MB Fast RAM at $01000000. EmuTOS uses it by itself; Atari's TOS 4.04 needs FASTRAM.PRG in the AUTO folder (extras/FASTRAM.PRG in the zip, source in tools/fastram/), as a real Falcon needs the driver of its accelerator card
Hard disks on SCSI	off	the hard disks are SCSI ID 0 and 1 (the Falcon's SCSI port) instead of IDE master and slave, for drivers that know the Falcon's SCSI but not IDE. EmuTOS and HDDRIVER work with both. Drivers that only know ACSI (the ST's hard disk port), such as older ICD PRO versions, do not start on the Falcon either way, as on a real Falcon. Takes effect with a reset

Drives & images (both machines)

Setting	Default	What it does
Write protect floppies	off	the floppy images are write protected
Swap floppy A: and B:	off	exchanges the drives, e.g. to boot from the disk in B:
Real floppy drive as A:	off	drive A: is the MEGA65's internal drive (read only, Real floppy drive)
Floppy read assist	✓ on	cleans up the internal drive's signal and re-reads bad sectors
Remember floppies	✓ on	the floppy images come back at the next start (needs fcmount)
Remember TOS/cartridge	✓ on	the chosen TOS (per machine) and cartridge come back at the next start; off: tos.img / tosfalc.img

Hard disks are always remembered.

Controllers & ports

Setting	Default	What it does
Mouse type: Atari mouse / joystick, Amiga mouse, C64 1351 mouse	Atari	the mouse in the mouse port (Usage)
Mouse port: Port 1, joystick port 2 / Port 2, joystick port 1	port 1	which MEGA65 port has the mouse
STe joypads	off	the MEGA65 joysticks on the enhanced joystick ports (STe, Falcon)
PMOD: RS232/MIDI/printer	off	serial, MIDI and printer port on the PMOD headers (PMOD headers)
Cubase dongle	off	a Cubase 2/3 dongle in the cartridge port (ST)
Keyboard: ST keys (positional) / As printed, US TOS / As printed, UK TOS	positional	the keyboard layout (Usage)

HDMI: 720p 50 Hz (default), 720p 60 Hz, 576p 50 Hz 4:3 or 5:4, 640x480, 720x480, 800x600, and "DVI mode (no sound)" for DVI monitors. VGA: 31 kHz (default), 15 kHz (RGB, SCART), 15 kHz with CSync, and scanlines 25/50/75 %. See Video.

Using disk images

The menu and the file browser

• Help opens and closes the menu. Cursor up/down moves, Return selects.
• Selecting "Floppy A:", "Floppy B:", "Hard disk 0:", "Hard disk 1:", "TOS:" or "Cartridge:" opens the file browser in /atarist. Cursor up/down selects a file, cursor left/right turns the page, Return opens a folder or mounts the file, Run/Stop cancels. F1 / F3 switch between the internal and the external SD card.
• The browser only shows the file types the core can use: .st (floppy), .hd, .img, .vhd (hard disk), .img, .rom (TOS), .stc, .img (cartridge).
• The menu shows the name of the mounted image next to the drive. To unmount (eject) a drive, select its line and press Space. The same on the "Cartridge:" line removes the cartridge: the ST restarts without it. On the "TOS:" line it removes the chosen TOS: the machine restarts with tos.img (ST) or tosfalc.img (Falcon).
• Cartridges are for the ST/STe. While the Falcon030 is selected, the menu refuses a cartridge image, and the Falcon does not see a cartridge that is still loaded for the ST. ST cartridges crashed the Falcon, and no Falcon cartridges are known (issue #27).
• With /atarist/fcmount on the SD card (in the release zip), the mounted images and the chosen TOS and cartridge are remembered and loaded again at the next start ("Remember floppies" and "Remember TOS/cartridge" in "Drives & images" switch this off for the floppies or the TOS).

Floppy disk images

1. Copy the .st image into /atarist on the SD card (or into a subfolder).
2. Press Help, select "Floppy A:" and choose the image.
3. To boot from it (most games): select "Reset" in the menu, or switch the MEGA65 off and on with fcmount on the SD card. A disk mounted while the ST is running is seen like a real disk change, e.g. to open it on the desktop.
4. Disk changes: when a game asks for disk 2, mount disk 2 on "Floppy A:" (no reset).
5. Saving: the ST writes into a copy in memory; about 2 seconds after the last write the core writes the image back to the SD card. The drive LED is yellow until that is done: don't switch off or remove the SD card while it is yellow. "Write protect floppies" (Drives & images) protects the images; "Swap floppy A: and B:" boots from the disk in B:.
6. New empty disk (e.g. for game saves): python3 tools/make_st_disk.py blank.st on your computer (see Floppy disks).

Hard disk images

1. Copy the image (.hd, .img or .vhd, up to 4 GB) into /atarist on the SD card.
2. Press Help, select "Hard disk 0:" and choose the image. Large images show "Scanning disk image..." for a moment.
3. Reset the ST ("Reset" in the menu). TOS only looks for hard disks when it starts, so a hard disk mounted while the desktop is shown does not appear without a reset. With fcmount the image is mounted at power on before the ST starts, so no reset is needed.
4. With EmuTOS, drive C: appears on the desktop by itself. With Atari TOS, the hard disk driver on the image (HDDRIVER, AHDI, ICD, ...) starts first and adds drive C:. If there is no C: icon, add it once with "Options" → "Install Disk Drive" (TOS 1.x) or "Install Icon" (TOS 2.06), then "Save Desktop".
5. Hard disk writes go straight to the SD card (no delay). The drive LED is red while the ST accesses the hard disk.

More about images, drivers and Hatari images: Hard disks.

FAQ

My image is not in the file browser. Only .st, .hd, .img, .vhd, .rom and .stc files are shown. .msa and .stx floppy images and .zip files are not supported: unzip them on your computer and convert .msa to .st (e.g. with Hatari's hmsa tool: hmsa game.msa writes game.st). .stx (Pasti, copy protected originals) cannot be converted.

The hard disk is mounted, but there is no drive C:. Reset the ST after mounting (see above). With Atari TOS the image needs a bootable hard disk driver, and a C: icon on the desktop. A quick test: boot the EmuTOS from the release zip. If EmuTOS shows C:, the image works and the problem is the driver or the desktop setup. (0.4.12 and 0.4.13 ejected a hard disk image restored at power-on again inside the core, so TOS did not see it; fixed in 0.4.14, issues #11 and #12.)

The game does not start from the floppy. Mount the disk on "Floppy A:" and reset the ST. Some games need a real Atari TOS (TOS 1.02 or 1.04 for the ST, see TOS), some need 512 KB or 1 MB of memory or the ST (not STe) machine type. A few images in circulation are defective, see Game notes.

Are my saves on the floppy kept? Yes, if the image is not write protected: wait until the drive LED is no longer yellow before switching off.

How do I get empty drives at the next start? Unmount the drives with Space in the menu. Without /atarist/fcmount on the SD card, all drives start empty anyway.

Some games of a hard disk game collection don't start. Most hard disk versions of games need 1 MB of ST RAM or more (512 KB is often not enough, e.g. on the R3/R3A), and some only work with certain TOS versions. If a game fails, try more RAM and another TOS, and compare with Hatari using the same image and TOS.

Can I use a folder of my PC as drive C: like in Hatari? No, that is an emulator feature ("GEMDOS drive"). The core needs a hard disk image, like a real ST.

TOS

Each machine has its own TOS: /atarist/tos.img for the ST family and /atarist/tosfalc.img for the Falcon030 are loaded at power on and when you switch to that machine. "TOS:" in the menu loads another TOS image (.img or .rom) for the machine that runs and restarts it (cold boot). With /atarist/fcmount on the SD card (in the release zip), this choice is remembered for that machine and loaded again at the next start and after switching back to it. Without fcmount, tos.img / tosfalc.img are used again after a power cycle. How this works with the two machines, in a table: New in 1.1.6.

Machine	TOS
Atari ST	192k TOS 1.00 - 1.04, 256k TOS 1.06 - 2.06, EmuTOS
Atari STe, Mega STe, STEroids	TOS 1.06 or newer (1.62, 2.06), EmuTOS
Falcon030	512k TOS 4.0x (4.04 tested), EmuTOS for the Falcon (512 KB)

A TOS of the wrong size for the machine is refused with a message.

Mega STe speed: like a real Mega STE, the Mega STe mode starts at 8 MHz with the cache off; TOS 2.06 does not switch it. Set 16 MHz and the cache in the XControl "General" panel (or with a speed utility). "STEroids" always runs at full speed and has no speed setting; tools that only know the real Atari models cannot measure it.

Which TOS? EmuTOS is in the release zip only because it is free and may be distributed (Atari's TOS may not). It is fine for GEM programs and for a first test, but some games crash with it. For games, use a real Atari TOS: TOS 1.02 or 1.04 for the ST (some games only run reliably with TOS 1.02), TOS 1.62 or 2.06 for the STe. Use a ROM image dumped from your own Atari.

TOS 1.06 and 1.62 start slowly: after a cold boot without a hard disk, the screen stays white for about 14 seconds (measured in the simulator) before the desktop appears. The TOS boot code waits for a hard disk on the ACSI bus; the ST has not hung.

Changing the memory size or the machine type: since 0.4.8 the ST restarts with a cold boot by itself (issue #7). In 0.4.7 and older it did not boot after such a change, because TOS keeps the old memory layout in RAM and trusts it at the next reset: load a TOS with "TOS" in the menu (or switch the MEGA65 off and on) after the change.

Real time clock

The ST has the clock chip of the Mega ST (Ricoh RP5C15 at $FFFC21), which TOS 1.02 and newer and EmuTOS use automatically. It shows the time of the MEGA65's real time clock: set the clock in the MEGA65 configuration utility. Setting the time on the ST (e.g. in the control panel) does not change the MEGA65 clock and is overwritten by it.

Hard disks

On the ST the hard disks are ACSI targets 0 and 1; on the Falcon030 they are the IDE master and slave (the Falcon has no ACSI port; HDDRIVER and EmuTOS work with IDE images, see Falcon030 (test)). With "Falcon030 settings" → "Hard disks on SCSI" they are SCSI ID 0 and 1 instead, for drivers that know the Falcon's SCSI but not IDE. A disk prepared on the ST with a driver that only knows ACSI, such as an older ICD PRO, does not boot on the Falcon (also not on a real one): TOS 4.04 starts its boot code, which then reads the disk over ACSI, finds no ACSI port and gives up without a message. Use EmuTOS, which reads such a disk by itself, or HDDRIVER. The images are raw disk images (as used by Hatari, MiSTer and MiST; .hd, .img or .vhd like on MiSTer, but not a Microsoft "dynamic" VHD), e.g. with a DOS (MBR) or Atari (AHDI) partition table. Images can be almost 4 GB large (the limit of FAT32); disks larger than 1 GB need a driver with ICD commands (EmuTOS, HDDRIVER). EmuTOS finds the partitions automatically; with Atari TOS you need a hard disk driver (AHDI, HDDRIVER, ...), e.g. on a boot floppy or on the hard disk itself.

Speed: the core reads and writes the images directly on the SD card, slower than a real hard disk (writing is the slowest part). Drivers wait long enough, with one exception: EmuTOS on the Falcon with "Hard disks on SCSI" gives up when a transfer takes longer than it would on a real disk, and shows "Your output device is not receiving data". The EmuTOS in the zip (tosfalc.img, from 1.5) allows at least 10 seconds per transfer; a copy of EmuTOS from the EmuTOS website does not, so with it use IDE (the default) instead of SCSI. A tester measured about 31 seconds for copying 1 MB (read and write, about 33 KB/s each way) on SCSI, IDE and with TOS 4.04 and the ICD driver alike.

A ready image for the Falcon: extras/falcon128.img in the zip is a blank 128 MB IDE image with four FAT16 partitions of 32 MB (C: to F:, "TOS & Windows compatible", no byte swapping). Copy it into /atarist, choose it as "Hard disk 0:" and reset: EmuTOS shows C: to F: by itself (it has no driver, so TOS 4.04 does not see it). To copy files onto it from a PC: on Linux sudo mount -o loop,offset=32768 falcon128.img /mnt (C:); on Windows a tool such as OSFMount. tools/make_falcon_hd.py makes other sizes (python3 make_falcon_hd.py --size 64 my.img).

How to use a hard disk image: see Hard disk images above.

Images that work in Hatari do not always work here:

• Hatari often uses a PC folder as drive C: ("GEMDOS drive"). That needs no driver and no image at all, so it works with any TOS. A real ST, and MegaST, needs a hard disk image with a driver.
• Hatari also emulates IDE and SCSI disks. The ST and STe only have ACSI; the image must be prepared for an ACSI disk (HDDRIVER and AHDI images usually are).
• An image without a bootable driver (e.g. created by Hatari's atari-hd-image tool, which writes a DOS partition table and no driver) works with EmuTOS, but with Atari TOS only together with a driver from a boot floppy.

A first test: if EmuTOS shows drive C: for the image, the image and the ACSI disk work, and any problem with Atari TOS is in the driver setup.

The images are not loaded into RAM: every sector is read from and written to the SD card directly (write-through). The FAT32 library of the framework can only seek from the start of a file, following the cluster chain; the firmware therefore remembers the cluster of every 2 MB of an image (4 MB for images larger than 1 GB, 8 MB above 2 GB) and seeks from there or from the current position (see M2M/rom/vd_fastseek.asm), so random access is fast in large images, too.

Floppy disks

The floppy disk images (.st, 360 kB to 1.44 MB) are loaded into the HyperRAM and written back to the SD card when the ST writes to them. "Swap floppy A: and B:" in "Drives & images" exchanges the drives, e.g. to boot from the disk in B:.

To create an empty, formatted disk (e.g. a save disk for a game), run python3 tools/make_st_disk.py blank.st on your computer (options: --size 360|720|800|1440, --label NAME) and copy the image into /atarist on the SD card. (The FDC emulation cannot format a disk, so formatting a disk image in TOS does not work.)

Real floppy drive

Since 1.1 the ST can use the MEGA65's internal 3.5" drive as drive A:. Switch on "Real floppy drive as A:" in "Drives & images" and choose "Reset". Drive A: is then the disk in the MEGA65's drive. Since 1.6 drive B: can still be a floppy image (mount it as "Floppy B:"), e.g. to copy a real disk to an image (issue #33; ST only, on the Falcon B: is not used while the real drive is on). Without an image B: is a missing drive, as on an ST with one drive. With EmuTOS this needs 1.1.1 or newer (1.1 showed no drive icons, issue #24). Up to 1.1.1 a reset took 5 to 10 seconds longer while the real drive was on (TOS waited for the missing drive B:); fixed in 1.1.2. With no disk in the drive, TOS still waits a moment for drive A:. Original ST disks are read as on a real ST: the core has a complete WD1772 floppy controller (WF1772IP by Wolfgang Förster), so copy protections and formats with 10 or 11 sectors and more than 80 tracks work.

• Read only: the core never writes to the disk. Programs that save to the disk (high scores, save games) get an error.
• DD disks only (the 720 KB type). HD disks are not supported.
• "Floppy read assist" (Drives & images, on by default): the MEGA65 drive's speed varies within each turn of the disk, more than an Atari drive's, and the WD1772 then misreads a sector now and then. Some loaders hang on such an error. With read assist the core cleans up the timing of the drive's signal and re-reads a sector that failed its checksum (up to 15 more turns) before the ST gets it. Switch it off only to compare.
• Weak disks: a disk that reads fine in a PC drive can still have weak spots. If a disk does not load, try it in a real ST or make a fresh copy (e.g. with a Greaseweazle) and report it in issue #15, with the board, the disk and the program.

Game notes

Tester reports about single games and disk images. Please report others in the issues, with the name and MD5 of the image.

Game / image	Note
Road Blasters (1988)(U.S. Gold).st (TOSEC, MD5 f3afdf00840c7e91b48d6b3daf8a4daf)	Defective image, also misbehaves in Hatari: no joystick control, and after a reset a long write back to the SD card (issues #8, #9). Use a different dump.
Gauntlet	Works; press Insert (MEGA65 No Scroll) to start the game (issue #9).

Video

• Falcon030: the VIDEL picture goes to HDMI and VGA like the ST's; its resolutions and colour depths are chosen in TOS or by programs, and the menu's "Monitor" setting only decides which modes are offered (see Falcon030 settings).
• HDMI: the image is scaled by ascal (4:3, with the border). "Zoom-in (hide border)" shows only the graphics area (320x200, 640x200 or 640x400) and uses the full width of 16:9 modes. The border is black on VGA in this mode.
• DVI monitors (HDMI-to-DVI cable or adapter): if the picture is garbled, enable "DVI mode (no sound)" in the HDMI settings. It switches off the HDMI audio and info packets that DVI monitors cannot decode. If the menu is unreadable on the DVI monitor, change the setting while a VGA monitor is connected (the setting is saved), or try a lower HDMI mode such as 800x600.
• VGA: the color modes are 15 kHz modes. By default they are doubled to 31 kHz for VGA monitors ("VGA: 31 kHz"), optionally with scanlines (25%, 50%, 75%). "15 kHz (RGB, SCART)" outputs the original 15 kHz signal for CRTs and TVs, "15 kHz with CSync" puts composite sync on the HSync pin (for MiSTer style VGA-to-SCART cables). The monochrome mode is output unchanged with the original SM124 timing (640x400, 71.2 Hz, 35.7 kHz), so the VGA monitor must accept that mode. "Mono 60 Hz" adds blank lines to get ~60 Hz (same 35.7 kHz line rate).
• HDMI and the 71 Hz mono mode: the HDMI output always runs at the HDMI mode's rate (50 or 60 Hz). ascal writes the 71 Hz frames into its frame buffer and reads them at the output rate, so some frames are dropped (about 1 in 6 at 60 Hz). Since 1.1.3 the frame buffer has 16 bits per pixel and three buffers: no flicker at 720p and no tear line. For smooth motion, enable "Mono 60 Hz" and use a 60 Hz HDMI mode.

Viking/SM194 card

Enable "Viking 1280x1024 card" in "ST/STe settings" and load a Viking driver. The card uses $C00000, so the ST RAM must be 8 MB or less (with more, the menu item has no effect); in the STEroids mode the card is at $E80000 and all 14 MB can be used. The MiST driver works: put mist_vhi.prg from mist-board/tools/mist_vhi into the AUTO folder, or boot from mist_vhi.st. It finds the card at either address. As soon as the driver accesses the card, the video output switches to the card. Switching the menu item on or off resets the ST (with the card off, the driver reports "No video memory found" and the ST starts as usual).

On HDMI, the picture is shown 1:1 at 1280x1024: while the Viking desktop is on screen, the HDMI output switches to 1280x1024 @ 60 Hz (108 MHz pixel clock, the VESA mode of 5:4 PC monitors) and back to the HDMI mode of the menu when the card is switched off. This mode is not a TV mode: PC monitors show it, many TVs do not. On VGA, 2x2 pixels are averaged into one of five grey levels: 640x512 @ 60 Hz, 31 kHz.

Falcon030 (test)

The Falcon030 is a test version. It boots EmuTOS and Atari's TOS 4.04, runs many Falcon programs and demos and starts FreeMiNT from a hard disk image, but it has seen much less testing than the ST. Please report what works and what does not in the issues.

The MEGA65 version was engineered for MegaST: the SDRAM memory controller, the 68882 FPU on a RISC-V CPU inside the FPGA, the MEGA65 integration, the menu, machine switching and TOS handling, and many fixes. Its CPU and chipset come from the open-source Falcon_MiSTer and AP68030 projects.

R6 only (it needs the SDRAM; not on the R3/R3A). Choose Machine: Falcon030 in the menu. Switching between the ST and the Falcon closes the menu, loads the TOS of the new machine and starts it.

TOS: the Falcon needs a Falcon TOS, the ST an ST TOS, and each machine has its own. At power on and after switching the machine in the menu, the core loads atarist/tos.img for the ST and atarist/tosfalc.img for the Falcon (EmuTOS for the Falcon, 512 KB, in the zip; from 1.4 with a longer time limit for hard disks on SCSI, see Hard disks and tools/emutos_scsi_timeout.py; the EmuTOS source is at emutos.sourceforge.io). A TOS loaded with the menu item "TOS:" replaces it for the machine that runs, and with fcmount on the SD card it is remembered for that machine: switching from the ST with TOS 2.06 to the Falcon and back gives the ST TOS 2.06 again. A TOS the machine cannot run is refused when you choose it (the ST cannot use a 512 KB TOS, the Falcon needs one). Without tosfalc.img the Falcon gets tos.img and does not start (the menu still works). Atari's TOS 4.04 works: copy your own TOS 4.04 image (512 KB) to the SD card and choose it with "TOS:" while the Falcon runs.

Hard disks under TOS 4.04: unlike EmuTOS, TOS 4.04 has no hard disk driver of its own. A disk works when a driver on it starts at boot. The HDDRIVER demo images from hddriver.net (hddrdemo130_ide.img on IDE, hddrdemo130_scsi.img with "Hard disks on SCSI") boot to the desktop with drive C: in the simulation; the demo only works with its own small images. For your own images use a full driver such as HDDRIVER. falcon128.img has no driver, so it works with EmuTOS only.

FreeMiNT: a FreeMiNT 1.19 installation on an IDE hard disk image (with HDDRIVER) boots: the kernel, its drivers, the network setup and the text shell work, and with GEM=ROM in mint.cnf TOS 4.04's own desktop runs under FreeMiNT. The XaAES desktop does not start yet: the screen turns white right after XaAES has loaded its kernel module (also without NVDI and without the video mode change); the MEGA65 menu still works. This is being worked on; until then use GEM=ROM. Reports with other FreeMiNT setups are welcome.

What it has

• 68030 with its caches and PMMU, 16 MHz like a real Falcon or 32 MHz ("CPU at 32 MHz (turbo)"; the turbo helps most with the caches on, see the menu reference)
• 68882 FPU (it runs on a small RISC-V CPU in the FPGA, so FPU-heavy programs are slower than on a real Falcon)
• VIDEL graphics: the ST modes and the Falcon modes with 2 to 256 colours and True Color; monitor type VGA, RGB, TV or mono (SM124). The "Monitor" setting is the monitor the Falcon believes is connected, not the MEGA65 output you use: it decides which video modes TOS and programs offer. The picture goes to HDMI and to the VGA connector with every setting, so "VGA (31 kHz)", the default, also works with an HDMI TV or monitor only (tested on an R6 over HDMI).
• DSP56001, DMA sound, the sound matrix and the YM2149
• 14 MB ST-RAM (or 4 MB) and optionally 48 MB of Fast RAM (TT-RAM) at $01000000
• Two floppy drives (.st images) and the MEGA65's internal drive as A:. Atari's TOS 4.04 uses drive A: only (B: is a second name for A:, as on a real Falcon); EmuTOS uses both
• Two IDE hard disks: "Hard disk 0:" is the IDE master, "Hard disk 1:" the slave (up to 4 GB), or SCSI ID 0 and 1 with "Hard disks on SCSI"
• Enhanced joystick ports (Jaguar style joypads and paddles via "STe joypads")
• Serial port and MIDI on the PMOD headers
• The NVRAM (boot video mode, language, boot drive) is saved on the SD card as /atarist/fcnvram

The settings are in the menu under "Falcon030 settings". Because the Falcon's menu is larger, the core keeps its settings and remembered images in /atarist/fccfg and /atarist/fcmount. Copy both from the zip: without fccfg the settings are not saved. The files stcfg and stmount of older versions stay untouched.

Not working or not tested yet

• Programs for a 68060 accelerator (CT60/CT63): the Falcon has a 68030
• FreeMiNT's XaAES desktop: white screen, see above (FreeMiNT with GEM=ROM works)
• Hard disk drivers other than EmuTOS's own and HDDRIVER (for example AHDI): not tested yet. ACSI-only drivers such as older ICD PRO versions cannot start on the Falcon (see the FAQ on hard disks)
• Microphone input: the MEGA65 has no audio input

PMOD headers (serial port, MIDI, printer)

When "PMOD: RS232/MIDI/printer" is enabled in the "Controllers & ports" menu, the PMOD headers are powered and used as follows (3.3V TTL levels, all inputs have pull-ups):

Pin	Signal	Pin	Signal
PMOD1 lo[0]	RS232 CTS (in)	PMOD1 hi[0]	MIDI OUT (out)
PMOD1 lo[1]	RS232 TXD (out)	PMOD1 hi[1]	MIDI IN (in)
PMOD1 lo[2]	RS232 RXD (in)	PMOD1 hi[2]	printer STROBE (out)
PMOD1 lo[3]	RS232 RTS (out)	PMOD1 hi[3]	printer BUSY (in)
PMOD2 lo[0..3]	printer D0..D3 (in/out)	PMOD2 hi[0..3]	printer D4..D7 (in/out)

PMOD1 lo matches the Digilent PMOD UART pinout (e.g. a PmodUSBUART or a MAX3232 module). MIDI needs the usual opto-coupler (IN) and driver (OUT) circuit. The parallel port pins also allow "Gauntlet" style joystick adapters.

MT32-pi: the MT32-pi reads serial MIDI with 3.3V levels on the GPIO UART of the Raspberry Pi (midi_in = gpio or the default configuration of the MT32-pi with a GPIO MIDI connection), so it can be connected without any MIDI circuit: PMOD1 hi[0] (MIDI OUT) to the RXD pin of the Pi (GPIO 15) and GND to GND. Its sound comes from the audio output of the Pi. (On MiSTer the MT32-pi audio is mixed into the core via I2S; this is not supported.)

Not supported (yet)

• Ethernec, MT32-pi audio mixing (MIDI to an MT32-pi works, see above)
• Jaguar pad buttons beyond fire on the STe joystick ports (the MEGA65 joysticks have one button)

Building and development

How the port works, the source files, the changes to the MiSTer core, the tests and how to build the core: see doc/DEVELOPMENT.md.

License

GPL v3, see LICENSE. The MiSTer core is licensed under GPL v2 or later (FX68K: GPL v3). TOS is copyrighted by Atari and is not part of this repository.