Box16

This is an emulator for the Commander X16 computer system. Unlike the official emulator, this has a few more dependencies, see the build instructions below. It compiles on Windows, Debian Linux, and Raspbian, and probably other Linux-based platforms.

Don't expect official "releases" until the physical X16 is out. Until then, there will be "non-releases" of Box16. Since this is originally forked from the Official X16 emulator, the goal is to remain fully compatible with the Official X16 emulator, but with feature-adds such as ImGui displays, and performance improvements from OpenGL acceleration.

Some of the feature-adds will be prototype or preview in nature, as this is also my platform for fixing bugs and adding features to the official emulator.

Features

CPU: Full 65C02 instruction set
VERA
- Mostly cycle exact emulation
- Supports almost all features:
  - composer
  - two layers
  - sprites
  - VSYNC, raster, sprite IRQ
Sound
- PCM
- PSG
- YM2151
SD card: reading and writing (image file)
VIA
- ROM/RAM banking
- keyboard
- mouse
- gamepad

Missing Features

VERA
- Does not support the "CURRENT_FIELD" bit
- Interlaced modes (NTSC/RGB) don't render at the full horizontal fidelity
VIA
- Does not support counters/timers/IRQs

Binaries & Compiling

The emulator itself is dependent on SDL2 and OpenGL. However, to run the emulated system you will also need a compatible rom.bin ROM image. This will be loaded from the directory containing the emulator binary, or you can use the -rom .../path/to/rom.bin option.

WARNING: Older versions of the ROM might not work in newer versions of the emulator, and vice versa.

You can build a ROM image yourself using the build instructions in the x16-rom repo. The rom.bin included in the latest release of the emulator may also work with the HEAD of this repo, but this is not guaranteed.

Linux Build

Read resources/r39/README and build or acquire the necessary files.

The needed development packages are available as a distribution package with most major versions of Linux:

Debian: sudo apt-get install libglew-dev libgtk-3-dev libsdl2-dev libsdl2-image-dev
Raspbian: sudo apt-get install libglew-dev libgtk-3-dev libsdl2-dev libsdl2-image-dev
Fedora 33: sudo dnf install glew-devel SDL2-devel SDL2_image-devel

Type make to build the source. The output will be box16 in the output directory. Remember you will also need a rom.bin as described above.

Windows Build

Read resources/r39/README and build or acquire the necessary files.

Install Microsoft Visual Studio Community 2019, make sure to include the following modules:

Desktop development with C++

Open build\vs2019\box16.sln with Visual Studio Community 2019. Select Build All from the Build menu.

The built .exe and associated files should be located in build\vs2019\out, plus a few more subdirectories based on the exact build generated.

Starting

You can start box16/box16.exe either by double-clicking it, or from the command line. The latter allows you to specify additional arguments.

When starting box16 without arguments, it will pick up the system ROM (rom.bin) from the executable's directory.
-abufs <number> Is provided for backward-compatibility with x16emu toolchains, but is non-functional in Box16.
-bas lets you specify a BASIC program in ASCII format that automatically typed in (and tokenized).
-debug <address> adds a breakpoint to the debugger.
-dump {C|R|B|V} configure system dump (e.g. -dump CB):
- C: CPU registers (7 B: A,X,Y,SP,STATUS,PC)
- R: RAM (40 KiB)
- B: Banked RAM (2 MiB)
- V: Video RAM and registers (128 KiB VRAM, 32 B composer registers, 512 B pallete, 16 B layer0 registers, 16 B layer1 registers, 16 B sprite registers, 2 KiB sprite attributes)
-echo [{iso|raw}] (e.g. -echo iso) causes all KERNAL/BASIC output to be printed to the host's terminal. Enable this and use the BASIC command "LIST" to convert a BASIC program to ASCII (detokenize):
- By default, everything but printable ASCII will be escaped.
- iso will escape everything but non-printable ISO-8859-1 characters and convert the output to UTF-8.
- raw will not do any substitutions.
-hypercall_path <path> sets the default path for all LOAD and SAVE calls to BASIC and the kernal.
-geos launches GEOS at startup.
-gif <file.gif>[,wait] records frames generated by the VERA to the specified gif file (e.g. -gif capture.gif or -gif capture.gif,wait)
- Recording normally begins immediately.
- ,wait will begin the gif file, but immediately pause recording.
- POKE $9FB5,0 will pause GIF recording
- POKE $9FB5,1 will snapshot a single frame
- POKE $9FB5,2 will unpause GIF recording
-help will show all command line options and their documentation, then immediately exit.
-keymap tells the KERNAL to switch to a specific keyboard layout. Use it without an argument to view the supported layouts.
-log enables one or more types of logging (e.g. -log KS):
- K: keyboard (key-up and key-down events)
- S: speed (CPU load, frame misses)
- V: video I/O reads and writes
-nobinds will disable most emulator keyboard bindings, allowing the X16 to see most keys and key chords.
-nosound can be used to specify that the audio subsystem should not be enabled in the first place.
-nvram lets you specify a 64 byte file for the system's non-volatile RAM. If it does not exist, it will be created once the NVRAM is modified.
-prg lets you specify a .prg file that gets injected into RAM after start.
-quality {nearest|linear|best} lets you specify video scaling quality.
-ram <ramsize> will adjust the amount of banked RAM emulated, in KB. (8, 16, 31, 64, ... 2048)
-rom <rom.bin> will allow you to override the KERNAL/BASIC/ROM file used by the emulator.
-rtc will set the real-time clock to the current system time and date.
-run executes the application specified through -prg or -bas using RUN or SYS, depending on the load address.
-scale {1|2|3|4} sizes the Box16 window to scale video output to an integer multiple of 640x480. (e.g. -scale 2)
-sdcard <sdcard.img> lets you specify an SD card image (partition table + FAT32).
-sound <device> lets you specify a specific sound device to use. If given an improper device or no device, will list all audio devices and exit.
-stds will automatically load all kernal and BASIC labels, if available.
-sym <filename> will load a VICE label file. Note that not all VICE debug commands are available. (e.g. -sym myprg.lbl)
-test {0, 1, 2, 3} will automatically invoke the TEST command with the provided test number.
-version will print the version of Box16 and then exit.
-warp causes the emulator to run as fast as possible, possibly faster than a real X16.
-wav <file.wav>[{,wait|,auto}] records audio to the specified wav file (e.g. -wav audio.wav or -wav audio.wav,wait)
- Recording normally begins immediately.
- ,wait will start with recording paused.
- ,auto will start with recording paused, but recording will automatically start at the first non-zero audio signal.
- POKE $9FB6,0 will pause wav recording
- POKE $9FB6,1 will unpause wav recording
- POKE $9FB6,2 will unpause wav recording at the fist non-zero audio signal
-ymirq will enable interrupts from the YM2151 audio chip (this is disabled by default to match the behavior of the official emulator r38)
-ymstrict will enable strict enforcement of the YM2151's busy status, dropping writes to the chip if it's busy at the time of write (this is disabled by default to match the behavior of the official emulator r38)

Run box16 -help to see all command line options.

Keyboard Layout

The X16 uses a PS/2 keyboard, and the ROM currently supports several different layouts. The following table shows their names, and what keys produce different characters than expected:

Name	Description	Differences
en-us	US	[`] ⇒ [←], [~] ⇒ [π], [\] ⇒ [£]
en-gb	United Kingdom	[`] ⇒ [←], [~] ⇒ [π]
de	German	[§] ⇒ [£], [´] ⇒ [^], [^] ⇒ [←], [°] ⇒ [π]
nordic	Nordic	key left of [1] ⇒ [←],[π]
it	Italian	[\] ⇒ [←], [\|] ⇒ [π]
pl	Polish (Programmers)	[`] ⇒ [←], [~] ⇒ [π], [\] ⇒ [£]
hu	Hungarian	[\] ⇒ [←], [\|] ⇒ [π], [§] ⇒ [£]
es	Spanish	[\|] ⇒ π, \ ⇒ [←], Alt + [<] ⇒ [£]
fr	French	[²] ⇒ [←], [§] ⇒ [£]
de-ch	Swiss German	[^] ⇒ [←], [°] ⇒ [π]
fr-be	Belgian French	[²] ⇒ [←], [³] ⇒ [π]
fi	Finnish	[§] ⇒ [←], [½] ⇒ [π]
pt-br	Portuguese (Brazil ABNT)	[\] ⇒ [←], [\|] ⇒ [π]

Keys that produce international characters (like [ä] or [ç]) will not produce any character.

Since the emulator tells the computer the position of keys that are pressed, you need to configure the layout for the computer independently of the keyboard layout you have configured on the host.

Use the F9 key to cycle through the layouts, or set the keyboard layout at startup using the -keymap command line argument.

The following keys can be used for controlling games:

Keyboard Key	NES Equivalent
Ctrl	A
Alt	B
Space	SELECT
Enter	START
Cursor Up	UP
Cursor Down	DOWN
Cursor Left	LEFT
Cursor Right	RIGHT

Functions while running

Ctrl + R will reset the computer.
Ctrl + V will paste the clipboard by injecting key presses.
Ctrl + S will save a system dump (configurable with -dump) to disk.
Ctrl + F and Ctrl + Return will toggle full screen mode.
Ctrl + = and Ctrl + + will toggle warp mode.
Ctrl + A will attach the SD Card image, if available.
Ctrl + D will detach the SD Card image.

On the Mac, use the Cmd key instead.

GIF Recording

With the argument -gif, followed by a filename, a screen recording will be saved into the given GIF file. Please exit the emulator before reading the GIF file.

If the option ,wait is specified after the filename, it will start recording on POKE $9FB5,2. It will capture a single frame on POKE $9FB5,1 and pause recording on POKE $9FB5,0.

PEEK($9FB5) returns a 0 if recording is disabled, 1 if recording is enabled but not active, 2 if snapshotting a single frame, and 3 if recording.

WAV Recording

With the argument -wav, followed by a filename, a audio recording will be saved into the given WAV file. Please exit the emulator before reading the WAV file.

If the option ,wait is specified after the filename, it will start recording on POKE $9FB6,1. If the option ,auto is specified after the filename, it will start recording on the first non-zero audio signal, or on POKE $9FB6,1. POKE $9FB6,0 will pause recording, and POKE $9FB6,2 will pause recording until the next non-zero audio signal.

PEEK($9FB6) returns 0 if recording is disabled, 1 if recording is enabled but not active, 2 if recording is paused waiting on a non-zero audio signal, and 3 if recording.

BASIC and the Screen Editor

On startup, the X16 presents direct mode of BASIC V2. You can enter BASIC statements, or line numbers with BASIC statements and RUN the program, just like on Commodore computers.

To stop execution of a BASIC program, hit the RUN/STOP key (Esc in the emulator), or Ctrl + C.
To insert characters, first insert spaces by pressing Shift + Backspaces, then type over those spaces.
To clear the screen, press Shift + Home.
The X16 does not have a STOP + RESTORE function.

SD Card Images

The command line argument -sdcard lets you attach an image file for the emulated SD card. Using an emulated SD card makes filesystem operations go through the X16's DOS implementation, so it supports all filesystem operations (including directory listing though DOS"$ command channel commands using the DOS statement) and guarantees full compatibility with the real device.

Images must be greater than 32 MB in size and contain an MBR partition table and a FAT32 filesystem. The file sdcard.img.zip in this repository is an empty 100 MB image in this format.

On macOS, you can just double-click an image to mount it, or use the command line:

# hdiutil attach sdcard.img
/dev/disk2              FDisk_partition_scheme
/dev/disk2s1            Windows_FAT_32                  /Volumes/X16 DISK
# [do something with the filesystem]
# hdiutil detach /dev/disk[n] # [n] = number of device as printed above

On Linux, you can use the command line:

# sudo losetup -P /dev/loop21 disk.img
# sudo mount /dev/loop21p1 /mnt # pick a location to mount it to, like /mnt
# [do something with the filesystem]
# sudo umount /mnt
# sudo losetup -d /dev/loop21

On Windows, you can use the OSFMount tool.

Host Filesystem Interface

If the system ROM contains any version of the KERNAL, and there is no SD card image attached, the LOAD ($FFD5) and SAVE ($FFD8) KERNAL calls (and BASIC statements) are intercepted by the emulator for device 8 (the default). So the BASIC statements will target the host computer's local filesystem:

  LOAD"$
  LOAD"FOO.PRG
  LOAD"IMAGE.PRG",8,1
  SAVE"BAR.PRG

Note that this feature is very limited! Manually reading and writing files (e.g. OPEN in BASIC) is not supported by the host filesystem interface. Use SD card images for this.

The emulator will interpret filenames relative to the directory it was started in. On macOS, when double-clicking the executable, this is the home directory.

To avoid incompatibility problems between the PETSCII and ASCII encodings, you can

use lower case filenames on the host side, and unshifted filenames on the X16 side.
use Ctrl+O to switch to the X16 to ISO mode for ASCII compatibility.
use Ctrl+N to switch to the upper/lower character set for a workaround.

Dealing with BASIC Programs

BASIC programs are encoded in a tokenized form, they are not simply ASCII files. If you want to edit BASIC programs on the host's text editor, you need to convert it between tokenized BASIC form and ASCII.

To convert ASCII to BASIC, reboot the machine and paste the ASCII text using Ctrl + V (Mac: Cmd + V). You can now run the program, or use the SAVE BASIC command to write the tokenized version to disk.
To convert BASIC to ASCII, start box16 with the -echo argument, LOAD the BASIC file, and type LIST. Now copy the ASCII version from the terminal.

Using the KERNAL/BASIC environment

Please see the KERNAL/BASIC documentation.

Debugger

There are a number of debugging windows that can be displayed:

Two independent memory dump windows.
A disassembly and CPU status window.
A VERA memory dump and status window.

The debugger keys are similar to the Microsoft Debugger shortcut keys, and work as follows

Key	Description
F1	resets the shown code position to the current PC
F2	resets the 65C02 CPU but not any of the hardware.
F5	is used to return to Run mode, the emulator should run as normal.
F9	sets the breakpoint to the currently code position.
F10	steps 'over' routines - if the next instruction is JSR it will break on return.
F11	steps 'into' routines.
F12	is used to break back into the debugger.

The STP instruction (opcode $DB) will break into the debugger automatically.

Effectively keyboard routines only work when the debugger is running normally. Single stepping through keyboard code will not work at present.

Forum

https://www.commanderx16.com/forum/

Wiki

https://github.com/commanderx16/x16-emulator/wiki

License

Release Notes

Non-Release 39.2 ("Hokkaido Jingu")

Internals
- Replaced the YM core with ymfm, a BSD 3-clause library.
- YM2151 now supports timers, IRQs, and strict enforcement of the busy status.
Removed a variety of redundant dll files (akumanatt)
Fixed anisotropic filtering for display ("best" scaling option).
Fixed middle mouse button support (ZeroByteOrg)
Fixed YM2151 reset (ZeroByteOrg)
Many overlays and UIs replaced or improved (akumanatt, et al)
- Added CPU visualization to show where/how the CPU is spending its time per frame.
- Added command-line parameter hints to tooltip on Options display.
- Added CPU stack to debugger
- Re-wrote PSG monitor (akumanatt)
- Added YM2151 monior (akumanatt)
- Improved Layer debugger (akumanatt)
- Improved Tile visualizer (akumanatt)
- Usability tweak to color picker
- Improved Sprite settings (akumanatt)
Added basic MIDI support, it is now possible to play with the X16's audio devices via MIDI control.
Fixed a variety of relatived and absolute pathing issues.
Added support for "break" VICE label command in VICE label files.
Moved YM2151 to r39 memory address
Performance improvements
- Faster rel instruction.
- Faster check for lo-RAM breakpoints.
Added WAV recorder

Non-Release 39.1 ("Kiyomizu-dera Temple")

Supporting hardware Rev2.
Removed NES controller support.
Added -nosound to explicity disable sound system init.
Added ini file, comparable to r39. Will regenerate the file based on current command line options if no ini file is present at load time. Entries are identical to the command line parameters. Command line parameters will overrule ini file values.
Internals
- Faster joystick implementation, now supporting hot-swapping.
- Even faster PS2.
- Rebuilt build script. Windows is now a VS2019 solution. Still no Mac, but Linux builds A-OK. Pls halp with iThings, PRs absolutely welcome.
Fixes VERA scaling for scaling values greater than $80.
Added a bunch of imgui windows for debugging and options. Full list, including new ones:
- Options
- Memory Dumps
- ASM Monitor
- CPU Visualizer
- VRAM Visualizer
- VERA Monitor
- Palette
- Layer Settings
- Sprite Settings
- PSG Monitor
Fixes ported from official emulator:
- PR 216, fixing occasional flicker and hang issues on Linux. (nigels-com)
- PR 317, fixing debugger break timing after hypercalls.
- PR 321, adjusting mouse state send rate. (Elektron72)
- PR 322, fixing vsync timing. (Elektron72)
- PR 323, fixing front/back porch terms, quantities, and use. (Elektron72)
- PR 349, adding Delete, Insert, End, Page Up, and Page Down keys. (stefan-b-jakobsson)

Non-Release 38.1 ("Kinkakuji Temple")

Internals
- Converted code to C++17, cleaned up all build warnings, save one.
- Converted build scripts to CMake, but lost Mac along the way. Halp fix pls?
- Converted rendering to OpenGL.
- Converted overlay to ImGUI.
- Unified keyboard-like input and data queues.
- Restructured memory access to provide real read-only access for the debugger. Also small speed boost.
- Rewrote the PS2 ports to be lean mean speed machines.
- Pulled non-VERA code out of VERA code.
Debugger is now always enabled, the command-line option now requires an address and is used to set breakpoints.

Official X16 Emulator Release Notes

Release 38 ("Kyoto")

CPU
- added WAI, BBS, BBR, SMB, and RMB instructions [Stephen Horn]
VERA
- VERA speed optimizations [Stephen Horn]
- fixed raster line interrupt [Stephen Horn]
- added sprite collision interrupt [Stephen Horn]
- fixed sprite wrapping [Stephen Horn]
- added VERA dump, fill commands to debugger [Stephen Horn]
- fixed VRAM memory dump [Stephen Horn]
SD card
- SD card write support
- Ctrl+D/Cmd+D detaches/attaches SD card (for debugging)
- improved/cleaned up SD card emulation [Frank van den Hoef]
- SD card activity/error LED support
- VERA-SPI: support Auto-TX mode
misc
- added warp mode (Ctrl+'+'/Cmd+'+' to toggle, or -warp)
- added '-version' shell option [Alice Trillian Osako]
- new app icon [Stephen Horn]
- expose 32 bit cycle counter (up to 500 sec) in emulator I/O area
- zero page register display in debugger [Mike Allison]
- Various WebAssembly improvements and fixes [Sebastian Voges]

Release 37 ("Geneva")

VERA 0.9 register layout [Frank van den Hoef]
audio [Frank van den Hoef]
- VERA PCM and PSG audio support
- YM2151 support is now enabled by default
- added -abufs to specify number of audio buffers
removed UART [Frank van den Hoef]
added window icon [Nigel Stewart]
fixed access to paths with non-ASCII characters on Windows [Serentty]
SDL HiDPI hint to fix mouse scaling [Edward Kmett]

Release 36 ("Berlin")

added VERA UART emulation (-uart-in, -uart-out)
correctly emulate missing SD card
moved host filesystem interface from device 1 to device 8, only available if no SD card is attached
require numeric argument for -test to auto-run test
fixed JMP (a,x) for 65c02
Fixed ESC as RUN/STOP [Ingo Hinterding]

Release 35

video optimization [Neil Forbes-Richardson]
added -geos to launch GEOS on startup
added -test to launch (graphics) unit test on startup
debugger
- switch viewed RAM/ROM bank with numpad + and numpad - [Kobrasadetin]
- optimized character printing [Kobrasadetin]
trace mode:
- prepend ROM bank to address in trace
- also prints 16 bit virtual regs (graph/GEOS)
fixes
- initialize memory to 0 [Kobrasadetin]
- fixed SYS hex argument
- disabled "buffer full, skipping" and SD card debug text, it was too noisy

Release 34

PS/2 mouse
support for text mode with tiles other than 8x8 [Serentty]
fix: programmatic echo mode control [Mikael O. Bonnier]

Release 33

significant performance optimizations
VERA
- enabled all 128 sprites
- correct sprite zdepth
- support for raster IRQs
SDL controller support using -joy1 and -joy2 [John J Bliss]
65C02 BCD fixes [Norman B. Lancaster]
feature parity with new LOAD/VLOAD features [John-Paul Gignac]
default RAM and ROM banks are now 0, matching the hardware
GIF recording can now be controlled from inside the machine [Randall Bohn]
Debugging
- Major enhancements to the debugger [kktos]
- -echo will now encode non-printable characters like this: \X93 for CHR$(93), -bas as well as pasting accepts this convention again
- -echo raw for the original behavior
- -echo iso for correct character encoding in ISO mode
- -ram to specify RAM size; now defaults to 512

Release 32

correct ROM banking
VERA emulation optimizations [Stephen Horn]
added -dump option to allow writing RAM, CPU state or VERA state to disk [Nils Hasenbanck]
added -quality option to change scaling algorithm; now defaults to "best" [Maurizio Porrato]
output of -echo can now be fed into UNIX pipes [Anonymous Maarten]
relative speed of emulator is shown in the title if host can't keep up [Rien]
fix: 6502 BCD arithmetic [Rien]
fix: colors (white is now white) [Rien]
fix: sprite flipping [jjbliss]

Release 31

VERA 0.8 register layout
removed -char (character ROM is now part of rom.bin)
GIF recording using -gif [Neil Forbes-Richardson]
numpad support [Maurizio Porrato]
fake support of VIA timers to work around BASIC RND(0)
default ROM is taken from executable's directory [Michael Watters]
emulator window has a title [Michael Watters]
-debug allows specifying a breakpoint [Frank Buss]
package contains the ROM symbols in rom.txt
support for VERA SPI

Release 30

Emulator:

VERA can now generate VSYNC interrupts
added -keymap for setting the keyboard layout
added -scale for integer scaling of the window [Stephen Horn]
added -log to enable various logging features (can also be enabled at runtime (POKE $9FB0+) [Randall Bohn])
changed -run to be an option to -prg and -bas
emulator detection: read $9FBE/$9FBF, must read 0x31 and 0x36
fix: -prg and -run no longer corrupt BASIC programs.
fix: LOAD,1 into RAM bank [Stephen Horn]
fix: 2bpp and 4bpp drawing [Stephen Horn]
fix: 4bpp sprites [MonstersGoBoom]
fix: build on Linux/ARM

Release 29

better keyboard support: if you pretend you have a US keyboard layout when typing, all keys should now be reachable [Paul Robson]
-debug will enable the new debugger [Paul Robson]
runs at the correct speed (was way too slow on most machines)
keyboard shortcuts work on Windows/Linux: Ctrl + F/R/S/V
Ctrl + V pastes the clipboard as keypresses
-bas file.txt loads a BASIC program in ASCII encoding
-echo prints all BASIC/KERNAL output to the terminal, use it with LIST to convert a BASIC program to ASCII
-run acts like -prg, but also autostarts the program
JMP $FFFF and SYS 65535 exit the emulator and save memory into the host's storage
the packages now contain the current version of the Programmer's Reference Guide (HTML)
fix: on Windows, some file load/saves may be been truncated

Release 28

support for 65C02 opcodes [Paul Robson]
keep aspect ratio when resizing window [Sebastian Voges]
updated sprite logic to VERA 0.7 – the layout of the sprite data registers has changed, you need to change your code!

Release 27

Command line overhaul. Supports -rom, -char, -sdcard and -prg.
ROM and char filename defaults, so box16 can be started without arguments.
Host Filesystem Interface supports LOAD"$"
macOS and Windows packaging logic in Makefile

Release 26

better sprite support (clipping, palette offset, flipping)
better border support
KERNAL can set up interlaced NTSC mode with scaling and borders (compile time option)

Release 25

sdcard: fixed LOAD,x,1 to load to the correct addressg
sdcard: all temp data will be on bank #255; current bank will remain unchanged
DOS: support for DOS commands ("UI", "I", "V", ...) and more status messages (e.g. 26,WRITE PROTECT ON,00,00)
BASIC: DOS command. Without argument: print disk status; with "$" argument: show directory; with "8" or "9" argument: switch default drive; otherwise: send DOS command; also accessible through F7/F8
Vera: cycle exact rendering, NTSC, interlacing, border

Release 24

SD card support
- pass path to SD card image as third argument
- access SD card as drive 8
- the local PC/Mac disk is still drive 1
- modulo debugging, this would work on a real X16 with the SD card (plus level shifters) hooked up to VIA#2PB as described in sdcard.c in the emulator surce

Release 23

Updated emulator and ROM to spec 0.6 – the ROM image should work on a real X16 with VERA 0.6 now.

Release 22

SYS65375 (SWAPPER) now also clears the screen, avoid ing side effects.

Release 21

support for $ and % number prefixes in BASIC
support for C128 KERNAL APIs LKUPLA, LKUPSA and CLOSE_ALL

Release 20

Toggle fullscreen using Cmd + F or Cmd + return
new BASIC instructions and functions:
- MON: enter monitor; no more SYS65280 required
- VPEEK(bank, address)
- VPOKE bank, address, value example: VPOKE4,0,VPEEK(4,0) OR 32 [for 256 color BASIC]

Release 19

fixed cursor trail bug
fixed f7 key in PS/2 driver
f keys are assigned with shortcuts now: F1: LIST F2: <enter monitor> F3: RUN F4: <switch 40/80> F5: LOAD F6: SAVE" F7: DOS"$ <doesn't work yet> F8: DOS <doesn't work yet>

Release 18

Fixed scrolling in 40x30 mode when there are double lines on the screen.

Release 17

video RAM support in the monitor (SYS65280)
40x30 screen support (SYS65375 to toggle)

Release 16

Integrated monitor, start with SYS65280 rom.bin is now 3*8 KB:
- 0: BASIC (bank 0 at $C000)
- 1: KERNAL ($E000)
- 2: UTIL (bank 1 at $C000)

Release 15

correct text mode video RAM layout both in emulator and KERNAL

Release 14

KERNAL: fast scrolling
KERNAL: upper/lower switching using CHR$($0E)/CHR$($8E)
KERNAL: banking init
KERNAL: new PS/2 driver
Emulator: VERA updates (more modes, second data port)
Emulator: RAM and ROM banks start out as all 1 bits

Release 13

Supports mode 7 (8bpp bitmap).

Release 12

Supports 8bpp tile mode (mode 4)

Release 11

The emulator and the KERNAL now speak the bit-level PS/2 protocol over VIA#2 PA0/PA1. The system behaves the same, but keyboard input in the ROM should work on a real device.

Release 10

updated KERNAL with proper power-on message

Release 9

LOAD and SAVE commands are intercepted by the emulator, can be used to access local file system, like this:
```
LOAD"TETRIS.PRG
SAVE"TETRIS.PRG
```
No device number is necessary. Loading absolute works like this:
```
LOAD"FILE.PRG",1,1
```

Release 8

New optional override load address for PRG files:
```
./x64emu rom.bin chargen.bin basic.prg,0401
```

Release 7

Now with banking. POKE40801,n to switch the RAM bank at $A000. POKE40800,n to switch the ROM bank at $C000. The ROM file at the command line can be up to 72 KB now (layout: 0: bank 0, 1: KERNAL, 2: bank 1, 3: bank 2 etc.), and the RAM that Cmd + S saves is 2088KB ($0000-$9F00: regular RAM, $9F00-$9FFF: unused, $A000+: extra banks)

Release 6

Vera emulation now matches the complete spec dated 2019-07-06: correct video address space layout, palette format, redefinable character set

Release 5

BASIC now starts at $0401 (39679 BASIC BYTES FREE)

Release 4

Cmd + S now saves all of memory (linear 64 KB for now, including ROM) to memory.bin, memory-1.bin, memory-2.bin, etc. You can extract parts of it with Unix "dd", like: dd if=memory.bin of=basic.bin bs=1 skip=2049 count=38655

Release 3

Supports PRG file as third argument, which is injected after "READY.", so BASIC programs work as well.

Release 2

STOP key support

Release 1

6502 core, fake PS/2 keyboard emulation (PS/2 data bytes appear at VIA#1 PB) and text mode Vera emulation
KERNAL/BASIC modified for memory layout, missing VIC, Vera text mode and PS/2 keyboard