BlastEm 0.4.1
-------------

Installation
------------

Extract this archive to a directory of your choosing. If you wish to change the
configuration settings, copy default.cfg to $HOME/.config/blastem/blastem.cfg 
and modify the copy. If you are on Windows, the config file should be placed in
%localappdata%\blastem. You may also whish to add the blastem directory to your
PATH environment variable.

NOTE: Prior to version 0.4.1, BlastEm was still using Unixy locations for config
and save files. If you're upgrading from a previous version on Windows, you will
need to move them manually. For config files, the relevant paths are in the
previous paragraph. For save files, move all the directories found in 
%userprofile%\.local\share\blastem to %localappdata%\blastem

Usage
-----

This version of BlastEm has an experimental GUI that is implemented as a Genesis
ROM running inside the emulator. This UI can be operated with either a mouse or
the first emulated gamepad. By default, both the keyboard and the first game
controller are mapped to said gamepad. For more information on bindings see the
Bindings section.

Some operations are currently only supported through the command line. To get a
list of supported command line options on Linux or OSX type:

    ./blastem -h
    
From within your BlastEm directory. On Windows type:
    
    blastem.exe -h
    
Lock-On Support
---------------

This version of BlastEm has some preliminary support for Sonic & Knuckles lock
on technology. This is only available from the command line at the moment. To
use it specify the Sonic & Knuckles ROM as the primary ROM and specify the ROM
to be locked on using the -o option. As an example:

    ./blastem ~/romz/sonic_and_knuckles.bin -o ~/romz/sonic3.bin
    
Please note that Sonic 2 lock-on does not work at this time. Additionally the
save RAM added by Sonic 3 won't work either.

Configuration
-------------

Configuration is read from the file at $HOME/.config/blastem/blastem.cfg on
Unix-like systems and %localappdata%\blastem\blastem.cfg if it exists.
Othwerise it is read from default.cfg from the same directory as the BlastEm
executable. Sections are denoted by a section name followed by an open curly 
bracket, the section's contents and a closing curly bracket. Individual
configuration values are set by entering the value's name followed by a space
or tab and followed by the desired value.

Bindings
--------

The keys subsection of bindings maps keyboard keys to gamepad buttons or UI
actions. The key name goes on the left and the action is on the right.
Most keys are named for the character they produce when pressed. For keys that
don't correspond to a normal character, check the list below:

  Name       | Description
  -----------------
  up           Up arrow
  down         Down arrow
  left         Left arrow
  right        Right arrow
  space
  tab
  backspace    Backspace on PC keyboards, Delete on Mac keyboards
  esc
  delete
  lshift       Left shift
  rshift       Right shift
  lctrl        Left control
  rctrl        Right control
  lalt         Left alt on PC keyboards, Option on Mac keyboards
  ralt         Right alt on PC keyboards, Option on Mac keyboards
  home
  end
  pageup
  pagedown
  f1
  f2
  f3
  f4
  f5
  f6
  f7
  f8
  f9
  f10
  f11
  f12
  select
  play
  search
  back

The pads subsection is used to map gamepads and joysticks. Analog axes are not
currently supported. An example configuration is provided in default.cfg to map
SDL joystick 0 to the first controller and SDL joystick 1 to the second
controller. The button assignments there work well for a 360 controller (at 
least on Linux, it's possible the physical button to button number is different
on other operating systems).

The mice subsection is used to map mice to emulated Mega/Sega mice. The default
configuration maps both the first and second host mice to the first emulated
mouse. This should not need modification for most users.

One special mapping deserves a mention. By default, the 'r' key is mapped to
ui.release_mouse. When operating in windowed mode the mouse has a capture
behavior. Mouse events are ignored until you click in the window. The mouse
will then be "captured" and the cursor will be both made invisible and locked
to the window. The ui.release_mouse binding releases the mouse so it can be
used normally.

IO
--

This section controls which peripherals are attached to the emulated console.
IO assignments can be overridden by the ROM database when appropriate. For
instance, games with mouse support can automatically use the mouse and games
that only support 3-button pads can automatically force an appropriate pad.
Unforunately, the ROM database is not yet exhaustive so manual configuration
may be needed here in some cases.

Video
-----

The video section contains settings that affect the visual output of BlastEm.

"width" is used to control the window size when not in fullscreen mode. The
height of the window is calculated from this value. Both width and height can
be overridden from the command line.

"vertex_shader" and "fragment_shader" define the GLSL shader program that
produces the final image for each frame. Shaders can be used to add various
visual effects or enhancements. Currently BlastEm only ships with the default
shader. If you write your own shaders, place them in 
$HOME/.config/blastem/shaders and then specify the basename of the new shader
files in the "vertex_shader" and "fragment_shader" config options. Note that
shaders are not available in the SDL fallback renderer.

"scanlines" controls whether there is any emulation of the gaps between display
lines that are present when driving a CRT television with a 240p signal. This
emulation is very basic at the moment so this option is off by default.

"vsync" controls whether the drawing of frames is synchronized to the monitor
refresh rate. Valid values for this setting are "off", "on" and "tear". The
latter will attempt to use the "late tear" option if it's available and normal
vsync otherwise. Currently it's recommended to leave this at the default of
"off" as BlastEm synchronizes to audio and does not yet have the necessary code
to fully handle conflicts between the audio rate and monitor refresh rate.
Additionally, the "turbo" feature does not function properly with vsync
enabled. These issues will be addressed in a future release. If you wish to use
vsync, please see the VSync section at the bottom of the README.

"fullscreen" controls whether BlastEm starts in fullscreen or windowed mode.
This can be overridden on the command line with the -f flag. If fullscreen
is set to "off", -f will turn it on. Conversely, if fullscreen is set to "on"
in the config, -f will turn it off.

Audio
-----

The audio section contains settings that affect the audio output of BlastEm.

"rate" selects the preferred sample rate for audio output. Your operating
system may not accept this value in which case a different rate will be chosen.
This should generally be either the native sample rate of your sound card or an
integral divisor of it. Most modern sound cards have a native output rate that
is a multiple of 48000 Hz so the default setting should work well for most users.

"buffer size" controls how large of a buffer uses for audio data. Smaller values
will reduce latency, but too small of a value can lead to dropouts. 512 works
well for me, but a higher or lower value may be more appropriate for your system.

"lowpass_cutoff" controls the cutoff, or knee, frequency of the RC-style
low-pass filter. The default value of 3390 Hz is supposedly what is present in
at least some Genesis/Megadrive models. Other models reportedly use an even
lower value.

Clocks
------

The clocks section contains settings that affect how fast things run.

"m68k_divider" describes the relationsip between the master clock (which is
53693175 Hz for NTSC mode and 53203395 Hz for PAL mode). The default value of 7
matches the real hardware. Set this to a lower number to overclock the 68000
and set it to a higher number to underclock it.

"max_cycles" controls how often the system is forced to synchronize all
hardware. BlastEm generally uses a sync on demand approach to synchronizing
components in the system. This can provide perfect synchronization for most
components, but since the Z80 can steal cycles from the 68000 at unpredictable
times 68000/Z80 synchronization is imperfect. The default value of 3420
corresponds to the number of master clock cycles per line. Larger numbers may
produce a modest performance improvement whereas smaller numbers will improve
68000/Z80 synchronization.

"speeds" controls the speed of the overall emulated console at different
presets. Preset 0 is the default speed and should normally be set to 100. The
other presets enable the slow/turbo mode functionality.

UI
--

The UI section contains settings that affect the graphical user interface.

"rom" determines the path of the Genesis/Megadrive ROM that implements the UI.
Relative paths will be loaded relative to the BlastEm executable.

Other Settings
--------------

"default_region" determines the console region that will be used when region
detection fails and when there are multiple valid regions. The default of 'U'
specifies a 60Hz "foreign" console. 

Debugger
--------

BlastEm has an integrated command-line debugger loosely based on GDB's
interface. The interface is very rough at the moment. Available commands in the
68K debugger are:
    b ADDRESS            - Set a breakpoint at ADDRESS
    d BREAKPOINT         - Delete a 68K breakpoint
    co BREAKPOINT        - Run a list of debugger commands each time
                           BREAKPOINT is hit
    a ADDRESS            - Advance to address
    n                    - Advance to next instruction
    o                    - Advance to next instruction ignoring branches to
                           lower addresses (good for breaking out of loops)
    s                    - Advance to next instruction (follows bsr/jsr)
    c                    - Continue
    bt                   - Print a backtrace
    p[/(x|X|d|c)] VALUE  - Print a register or memory location
    di[/(x|X|d|c)] VALUE - Print a register or memory location each time
                           a breakpoint is hit
    vs                   - Print VDP sprite list
    vr                   - Print VDP register info
    zb ADDRESS           - Set a Z80 breakpoint
    zp[/(x|X|d|c)] VALUE - Display a Z80 value
    q                    - Quit BlastEm
Available commands in the Z80 debugger are:
    b  ADDRESS           - Set a breakpoint at ADDRESS
    de BREAKPOINT        - Delete a Z80 breakpoint
    a  ADDRESS           - Advance to address
    n                    - Advance to next instruction
    c                    - Continue
    p[/(x|X|d|c)] VALUE  - Print a register or memory location
    di[/(x|X|d|c)] VALUE - Print a register or memory location each time
                           a breakpoint is hit
    q                    - Quit BlastEm

The -d flag can be used to cause BlastEm to start in the debugger.
Alternatively, you can use the ui.enter_debugger action (mapped to the 'u' key
by default) to enter the debugger while a game is running. To debug the menu
ROM, use the -dm flag.

GDB Remote Debugging
--------------------

In addition to the native debugger, BlastEm can also act as a GDB remote
debugging stub. To use this, you'll want to configure your Makefile to produce
both an ELF executable and a raw binary. Invoke an m68k-elf targeted gdb with
the ELF file. Once inside the gdb session, type:

    target remote | BLASTEM_PATH/blastem ROM_FILE.bin -D

where BLASTEM_PATH is the relative or absolute path to your BlastEm
installation and ROM_FILE.bin is the name of the raw binary for your program.
BlastEm will halt at the beginning of your program's entry point and return
control to GDB. This will allow you to set breakpoints before your code runs.

On Windows, the procedure is slightly different. First run 
    blastem.exe ROM_FILE.bin -D
This will cause BlastEm to wait for a socket connection on port 1234. It will
appear to be frozen until gdb connects to it. Now open the ELF file in gdb
and type:

    target remote :1234

Trace points and watch points are not currently supported.

Included Tools
--------------

BlastEm ships with a few small utilities that leverage portions of the emulator
code.
    
    dis       - 68K disassembler
    zdis      - Z80 disassembler
    vgmplay   - Very basic VGM player
    stateview - GST save state viewer
    
VSync
-----

This section includes information about using VSync with BlastEm. As mentioned
above, the code is currently designed to only sync to audio and has some issues
with VSync as a result. That said, if your computer is fast enough and you
don't care about turbo mode, it can generally made to work.

The native refresh rate of an NTSC Genesis is approximately 59.92 Hz which is
probably not the native refresh rate of your monitor. Fortunately, it is
most likely lower than your refresh rate. As long as this is true, VSync will
generally work as long as your computer is fast enough to cope with the time
lost waiting for VSync and the audio buffer is large enough to not run out of
samples during that delay. Latency will suffer a bit and you'll get a doubled
frame, but things will be fine.

If you enable VSync and you're getting audio dropouts, first try doubling the
audio buffer setting. If you still experience dropouts, it's possible your
computer is not fast enough or that your monitor's actual refresh rate is in
fact lower than that of the emualted console. Not much can be done about the
former (apart from disabling VSync), but the latter can be dealt with by
lowering the default speed slightly in the "clocks" section.

A future release will support VSync in a less hacky fashion.

Special Thanks
--------------

My work has been made much easier by the contributions of those in the Genesis
community past and present. I'd like to thank the people below for their help.

Nemesis            - His work reverse engineering and documenting the VDP and
                     YM-2612 has saved me an immeasurable amount of time. I've
                     found both his sprite overflow test ROM and VDP FIFO
                     Testing ROM to be quite helpful.

Charles MacDonald  - While it hasn't been updated in a while, I still find his
                     VDP document to be my favorite reference. His Genesis
                     hardware document has also come in handy.

Eke-Eke            - Eke-Eke wrote a great document on the use of I2C EEPROM in
                     Genesis games and also left some useful very helpful 
                     comments about problematic games in Genesis Plus GX

Bart Trzynadlowski - His documents on the Genecyst save-state format and the
                     mapper used in Super Street Fighter 2 were definitely
                     appreciated.
                     
KanedaFR           - Kaneda's SpritesMind forum is a great resource for the
                     Sega development community.

I'd also like to thank the following people who have performed compatibility
testing or submitted helpful bug reports

micky, Sik, Tim Lawrence, ComradeOj, Vladikcomper

License
-------

BlastEm is free software distributed under the terms of the GNU General Public
License version 3 or higher. This gives you the right to redistribute and/or
modify the program as long as you follow the terms of the license. See the file
COPYING for full license details.

Binary releases of BlastEm are packaged with GLEW and SDL2 which have thier own
licenses. See GLEW-LICENSE and SDL-LICENSE for details.