JimmyStones / Aznable

Aznable (custom 8-bit computer system)

Overview

Acknowledgements

Hardware

Aznable is a (no longer) simple-ish bespoke (i.e. I made it up with no real plan) 8-bit multipurpose computer system, utilised by the MiSTer Input Test core.

Graphics:

• 40x30 character display (each character foreground and background colour can be set independently to one of 256 colours, using an extended C64 'Petscii' character set)
• Hardware sprites - 32 concurrent sprites, selectable 8x8/16x16/32x32 size, with a 32 colour palette out of 32768)
• Variable speed 3 layer LFSR-based starfield

Sound:

• YM music playback system (YM5/YM6 format only) using a YM2149 synth
• Audio sample playback (4-bit 8Khz) using an OKI M5205

All relevant MiSTer inputs are mapped into memory regions for the CPU to access directly. There is also a dedicated microsecond timer (runs 0-32677, resettable by writing to any bit of the address).

Components

• Z80 CPU (tv80 by Guy Hutchison, based on VHDL T80 core by Daniel Wallner)
• jtframe_vtimer for VGA timing (from JTFRAME (https://github.com/jotego/jtframe) by Jotego)
• jtframe_cen24 for clock enables (from JTFRAME (https://github.com/jotego/jtframe) by Jotego)
• 32Kb program ROM (port 1 cpu, port 2 download)
• 16Kb work RAM (port 1 cpu)
• 2Kb character ROM (port 1 cpu, port 2 download)
• 2Kb character RAM (port 1 cpu, port 2 charmap)
• 2Kb foreground colour RAM (port 1 cpu, port 2 graphics)
• 2Kb background colour RAM (port 1 cpu, port 2 graphics)
• 128b sprite register RAM (port 1 cpu, port 2 graphics)
• 2Kb sprite linebuffer RAM (port 1 write, port 2 read)
• 64b palette ROM (port 1 8-bit download, port 2 16-bit read)
• 8Kb sprite ROM (port graphics, port 2 download)
• 9 Memory-mapped IO regions. Yes I know about MREQ but SFRs turned out to be annoying in sdcc so :)
  • Hardware state (H/V Sync, H/V Blank etc) (8 bytes, read-only)
  • joystick_5->0 from HPS (192 bytes, read-only)
  • joystick_l_analog_5->0 from HPS (96 bytes, read-only)
  • joystick_r_analog_5->0 from HPS (96 bytes, read-only)
  • paddle_5->0 from HPS (48 bytes, read-only)
  • spinner_5->0 from HPS (96 bytes, read-only)
  • ps2_key from HPS (11 bytes, read-only)
  • ps2_mouse from HPS (48 bytes, combination of ps2_mouse and ps2_mouseext with some padding to align bytes)
  • timestamp from HPS (33 bytes, read-only)
• Hardware microsecond timer (16 bytes read/write)
• Hardware sprite engine (32 sprites, 8x8/16x16/32x32 pixels, 32 colour palette out of 32768)
• Hardware YM2149-based music player (YM2149 module (https://github.com/jotego/jt49) by Jotego)
• Hardware OKI M5205-based wave sample player (M5205 module (https://github.com/jotego/jt5205) by Jotego)
• LFSR-based starfield generator (from Project F - Ad Astra (https://projectf.io/posts/fpga-ad-astra/) by Will Green)

Memory Map (CPU addressable)

Start	Length	Name
0x0000	0x8000	Program ROM
0x8000	0x0001	System inputs (video signals)
0x8080	0x0020	Timestamp
0x80C0	0x0010	Timer
0x8100	0x00C0	Joystick inputs
0x8200	0x0060	Analog left inputs
0x8280	0x0060	Analog right inputs
0x8300	0x0030	Paddle inputs
0x8380	0x0060	Spinner inputs
0x8400	0x000C	PS2 keyboard input
0x8480	0x0030	PS2 mouse input
0x8500	0x0010	Starfield 1
0x8510	0x0010	Starfield 2
0x8520	0x0010	Starfield 3
0x8530	0x0001	System pause trigger
0x8531	0x0001	System menu trigger
0x8580	0x0010	Sound RAM (OKI M5205)
0x8590	0x0010	Music RAM (YM2149 Player)
0x8600	0x0010	Tilemap control RAM
0x8610	0x0300	Tilemap index RAM
0x9000	0x0800	Char ROM
0x9800	0x0800	Char Index RAM
0xA000	0x0800	Char Foreground Colour RAM
0xA800	0x0800	Char Background Colour RAM
0xB000	0x0080	Sprite RAM
0xB400	0x0004	Sprite Collision RAM
0xB800	0x0800	Sprite Linebuffer RAM
0xC000	0x4000	Work RAM

Software

/src contains a C program compiled to Z80 assembly using sdcc.

All required ROMs (compiled program and default MiSTer font) are built into the core when compiled with Quartus.

Selecting Load BIOS in the core allows hot loading of binary OS ROM files for easier development. Selecting Load Sprite ROM in the core allows hot loading of updated sprite ROM data.

Building the OS

Required packages

• sdcc
• srecord

Build steps

• Run make in /src/Makefile to create binary ROM
• Run od -An -t x1 -v src/os.bin > rtl/rom.hex to create hex version of ROM for Quartus build

License

This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.