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README.zorig
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This is a reconstruction of an 1980s-era Apple ][+ implemented in VHDL for
FPGAs.
Stephen A. Edwards, sedwards@cs.columbia.edu
http://www1.cs.columbia.edu/~sedwards
------------------------------
The current implementation uses the Altera DE2 board and takes advantage
of its off-chip SRAM, VGA DAC, SD card, audio CODEC, and PS/2 keyboard
interface.
It was designed to be fairly easy to port: the apple2.vhd file should
be implementation-agnostic: it only assumes the external availability
of 48K of RAM and a keyboard.
It contains a simple read-only Disk II emulator that expects
"nibblized" disk images written raw onto an SD or MMC card (i.e., it
does not use a FAT or any other type of filesystem).
The VGA controller (not part of an original Apple) doubles each line
and interprets the Apple's NTSC-compatible color signals to produce a color
640 X 480 VGA display with non-standard dot timing.
------------------------------
To compile under Altera's Quartus software, open the apple2fpga.qpf
project file and compile.
------------------------------
VHDL files, in order of elaboration:
timing_generator.vhd Timing signal generation, video counters
character_rom.vhd The beautiful 5 X 8 uppercase-only text font
video_generator.vhd Text, lores, and hires mode shift registers
main_roms.vhd D000-FFFF ROMs: Applesoft and the Monitor
cpu6502.vhd The 6502 CPU core
apple2.vhd Top-level of the Apple: mostly address decode
disk_ii_rom.vhd C600-C6FF ROM: Disk II bootstrap ROM
disk_ii.vhd Read-only Disk II emulator
vga_controller.vhd NTSC-to-VGA color interpolation, line doubler
PS2_Ctrl.vhd Low-level PS/2 keyboard interface
keyboard.vhd PS/2 keyboard-to-Apple interface
spi_controller.vhd SD/MMC card controller: reads raw tracks
i2c_controller.vhd Simple I2C bus driver; initializes the codec
wm8731_audio.vhd Controller for the Wolfson WM8731 audio codec
DE2_TOP.vhd Top-level entity for the Altera DE2 board
CLK28MPLL.vhd Altera-specific configuration for 28 MHz PLL
Other files:
dsk2nib.c Converts a 140K .dsk image file to the raw 228K
.nib format used by the Disk II emulator
makenibs A shell (e.g., bash) script that assembles
collections of .dsk files into a file suitable
for directly writing onto an SD card
rom2vhdl Script to convert raw ROM files into
synthesizable VHDL code. Used to produce main_roms.vhd
apple2fpga.qpf Project file for Altera's Quartus
DE2_TOP.qsf Mostly pin assignments for Altera's Quartus
DE2_TOP.sof A compiled bitstream for the DE2 board: the
result of compiling all the VHDL files in
Quartus; suitable for programming if you have a
DE2 board.
dos33master.nib Bootable disk image: Apple DOS 3.3 system master
bios.a65 6502 assembly source for a "fake" BIOS
bios.rom Binary data for the "fake" BIOS
Makefile Rules for creating the .zip, .vhd files, etc.
------------------------------
Disk images
The system expects a sequence of "nibblized" (227K) disk images on the
SD card starting at block 0. Switches on the DE2 board selects which
image appears to be in the drive; the image number is displayed in hex
on two of the seven-segment displays.
Most Apple II disk images are in 140K .dsk files, which stores only
the disk's logical data, i.e., is not encoded. dsk2nib.c is a small C
program that expands .dsk files to .nib files.
I used the "makenibs" script to find all the .dsk files in a tree of
directories, assemble them into an image suitable for downloading to
the SD card, and print an image number/file name cross-listing.
To write .nib images to an SD/MMC card under Linux, I use
dd if=dos33master.nib of=/dev/sdd
Of course, your card may appear as something other than /dev/sdd.
------------------------------
ROMs
This archive does NOT include a copy of the Apple ][+'s ROMs, which
are copyright Apple Computer. Instead, it includes a very trivial
BIOS that beeps, displays a text screen, then cycles through some
lores and hires graphics patterns when keys are pressed. This should
be enough to verify the graphics, sound, and keyboard are working (but
not the disk emulator). Source for this BIOS is in the bios.a65 file,
which I assembled using the xa65 cross-assembler.
The system requires two ROM images: a 12K image of the system roms
(memory from 0xD000 - 0xFFFF) and a 256-byte image of the Disk II
controller bootstrap ROM (memory from 0xc600 - 0xc6ff if the card is
in the usual slot 6).
Once you obtain them, run the "rom2vhdl" script to convert the binary
files into .vhd files that hold the data. The Makefile contains rules
for doing this.
------------------------------
Credits:
Peter Wendrich supplied the 6502 core:
-- cpu65xx_fast.vhdl, part of FPGA-64, is made available strictly for personal
-- educational purposes. Distributed with apple2fgpa with permission.
--
-- Copyright 2005-2008 by Peter Wendrich (pwsoft@syntiac.com).
-- All rights reserved.
-- http://www.syntiac.com/fpga64.html
The low-level PS/2 keyboard controller is from ALSE:
-- PS2_Ctrl.vhd
-- ------------------------------------------------
-- Simplified PS/2 Controller (kbd, mouse...)
-- ------------------------------------------------
-- Only the Receive function is implemented !
-- (c) ALSE. http://www.alse-fr.com
I adapted the Apple ][ keyboard emulation from Alex Freed's FPGApple:
http://mirrow.com/FPGApple/