SNK M68000 (Prehistoric Isle) FPGA Implementation

FPGA compatible core of SNK M68000 (Prehistoric Isle in 1930 based) arcade hardware for MiSTerFPGA written by Darren Olafson with assistance from atrac17.

The intent is for this core to be a 1:1 playable implementation of Prehistoric Isle in 1930 arcade hardware. Pending PCB verification, on loan from XtraSmiley.

External Modules

Module	Function	Author
fx68k	Motorola 68000 CPU	Jorge Cwik
t80	Zilog Z80 CPU	Daniel Wallner
jtopl2	Yamaha OPL 2	Jose Tejada
jt7759	NEC µPD7759	Jose Tejada
yc_out	Y/C Video Module	Mike Simone
mem	SDRAM Controller / Rom Downloader	Josh Bassett, modified by Darren Olafson
core_template	MiSTer Framework Template	sorgelig, modified by Darren Olafson / atrac17

Known Issues / Tasks

• OPL2 Audio [Issue]
• Timing issues with jtframe_mixer module; false paths added to sdc (may need refactor?) [Task]

PCB Check List

FPGA implementation loosely based on mame source and will be verified against an authentic SNK Prehistoric Isle in 1930 PCB.

Clock Information

H-Sync	V-Sync	Source
15.625kHz	54.065743Hz	OSSC OSSC

Crystal Oscillators

Freq (MHz)	Use
4.000	Z80 (4 MHz) YM3812CLK (4 MHz) µPD7759 (640 KHz)
18.000	M68000 (9 MHz)
12.000	Pixel CLK (6 MHz)

Pixel clock: 6.00 MHz

Estimated geometry:

384 pixels/line

289 pixels/line

Main Components

Chip	Use
Motorola 68000 CPU	Main CPU
Zilog Z80 CPU	Sound CPU
Yamaha YM3812	OPL2
NEC µPD7759	ADPCM Decoder

Core Features

Video Timings

• Video timings can be modified if you experience sync issues with CRT or modern displays; this will alter gameplay from it's original state.

Refresh Rate	Timing Parameter	HTOTAL	VTOTAL
15.63kHz / 54.1Hz	PCB	384	289
15.63kHz / 59.2Hz	NTSC (Closest Spec) / MAME	384	264

P1/P2 Input Swap Option

• There is a toggle to swap inputs from Player 1 to Player 2. This only swaps inputs for the joystick, it does not effect keyboard inputs.

Audio Options

• There is a toggle to disable playback of OPL2 / µPD7759 audio. There are toggles to adjust the volume of OPL2 and the µPD7759 audio.

Overclock Options

• There is a toggle to increase the M68000 frequency from 9MHz to 12MHz; this will alter gameplay from it's original state.

Native Y/C Output

• Native Y/C ouput is possible with the analog I/O rev 6.1 pcb. Using the following cables, HD-15 to BNC cable will transmit Y/C over the green and red lines. Choose an appropriate adapter to feed Y/C (S-Video) to your display.

H/V Adjustments

• There are two H/V toggles, H/V-sync positioning adjust and H/V-sync width adjust. Positioning will move the display for centering on CRT display. The sync width adjust can be used to for sync issues (rolling, flagging etc) without modifying the video timings.

Scandoubler Options

• Additional toggle to enable the scandoubler without changing ini settings and new scanline option for 100% is available, this draws a black line every other frame. Below is an example.

Scandoubler Fx	Scanlines 25%	Scanlines 50%	Scanlines 75%	Scanlines 100%

PCB Information / Control Layout

Title	Joystick	Service Menu	Dip Switches	Shared Controls	Dip Default	PCB Information
Prehistoric Isle in 1930 Genshitou 1930s	8-Way	Service Menu	Dip Sheet	Co-Op	Upright	There is a level select dipswitch not documented in the manual, when toggled you can select to start at any stage or view the end credits. There are two hidden cheat functions when setting dipswitches in certain positions. These enable a "pause" function which halts the CPU and infinite lives. These are labeled clearly in the dip switch menu for convenience.

Keyboard Handler

• Keyboard inputs mapped to mame defaults for all functions.

Services	Coin/Start
Functions Keymap Test F2 Reset F3 Service 9 Pause P	Functions Keymap P1 Start 1 P2 Start 2 P1 Coin 5 P2 Coin 6

Player 1	Player 2
Functions Keymap P1 Up Up P1 Down Down P1 Left Left P1 Right Right P1 Bttn 1 L-Ctrl P1 Bttn 2 L-Alt P1 Bttn 3 Space	Functions Keymap P2 Up R P2 Down F P2 Left D P2 Right G P2 Bttn 1 A P2 Bttn 2 S P2 Bttn 3 Q

Support

Please consider showing support for this and future projects via Darren's Ko-fi and atrac17's Patreon. While it isn't necessary, it's greatly appreciated.

Licensing

Contact the author for special licensing needs. Otherwise follow the GPLv2 license attached.