Add a ready-to-use disk image. Update README.

README.md

@@ -1,33 +1,92 @@
-Oberon RISC Emulator
-====================
+# Oberon RISC Emulator
 
-This is an emulator for the Oberon RISC machine. For more information, see:
-http://www.inf.ethz.ch/personal/wirth/ and http://projectoberon.com/.
+This is an emulator for the Oberon RISC machine. For more information,
+[see Niklaus Wirth's site](https://www.inf.ethz.ch/personal/wirth/). For
+newcomers to the Oberon family of operating systems, the document
+[Using Oberon] in the [Project Oberon section] is a must-read.
 
-Requirements: a C99 compiler (e.g. [GCC](http://gcc.gnu.org/),
-[clang](http://clang.llvm.org/)) and [SDL2](http://libsdl.org/).
+[Using Oberon]: https://www.inf.ethz.ch/personal/wirth/ProjectOberon/UsingOberon.pdf
+[Project Oberon section]: https://www.inf.ethz.ch/personal/wirth/ProjectOberon/index.html
 
-A suitable disk image can be downloaded from http://projectoberon.com/ (in
-S3RISCinstall.zip).
+![Screenshot][po2013.png]
+
+## Building
+
+To build the emulator, you need the SDL2 library and a C compiler that
+understands C99 (GCC and clang are fine).
+
+[SDL2]: http://libsdl.org/
+
+### Linux
+
+To install the needed packages on Debian, Ubuntu and derived
+distributions, use this command:
+
+    sudo apt-get install build-essential libsdl2-dev
+
+See your distribution's documentation if you're using something else.
+
+After that, build the emulator using the command `make`.
+
+### OS X
+
+I can't give much support for OS X, but I've had many reports saying
+it works fine. The main stumbling block seems to be that there are two
+ways to install the SDL development files: Unix style and Xcode style,
+as explained in the [SDL Mac OS X FAQ].
+
+For Unix style, build using the command `make`.
+For Xcode style, use `make osx`.
+
+[SDL Mac OS X FAQ]: https://wiki.libsdl.org/FAQMacOSX
+
+### Windows
+
+There's a pre-compiled version in Github's Releases section.
+
+See the [SDL site][SDL2]  for how to set up a compiler
+for Windows. It's fiddly.
+
+Alternatively, you can set up a cross compiler from Linux, which is
+also rather fiddle, and build with a command such as: (This is mostly
+for my own future reference.)
+
+    make CC=i686-w64-mingw32-gcc-win32 \
+         SDL2_CONFIG=/usr/local/cross-tools/i686-w64-mingw32/bin/sdl2-config
 
 
-Command line options
---------------------
+## Disk image
 
-Usage: `risc [options] disk-image.img`
+You can find an up-to-date disk image in the [DiskImage/](DiskImage/)
+directory. These images contain a full Project Oberon 2013 system,
+with all source code, symbol files, etc.
+
+They also have a few tweaks for better integration with the emulator
+(though it should still work fine on real hardware):
+
+* The Display module supports variable display resolution. (The
+  original module was hardcoded for 1024x768.)
+
+* There's a Clipboard module for basic clipboard integration,
+  documented below.
+
+The source code for these modifications can be found in the
+[Mods/](Mods/) directory.
+
+
+## Command line options
+
+Usage: `risc [options] disk-image.dsk`
 
 * `--fullscreen` Start the emulator in fullscreen mode.
 * `--size <width>x<height>` Use a non-standard window size.
-  This requires modified Display and Input modules, see
-  [the Oberon directory](Oberon/).
 * `--serial-fd <fd>` Send serial I/O to file descriptor fd (input) and
   fd+1 (output). (You probably won't need this.)
 
 
-Keyboard and mouse
-------------------
+## Keyboard and mouse
 
-The Oberon system assumes you have a US keyboard and a three button mouse.
+The Oberon system assumes you use a US keyboard layout and a three button mouse.
 You can use the left alt key to emulate a middle click.
 
 The following keys are available:
@@ -36,33 +95,31 @@ The following keys are available:
 * `F12` Soft-reset the Oberon machine.
 
 
-Transferring files
-------------------
+## Transferring files
 
 First start the PCLink1 task by middle-clicking on the PCLink1.Run command.
 Transfer files using the pcreceive.sh and pcsend.sh scripts.
 
+Alternatively, use the clipboard integration to exchange text.
 
-Clipboard integration
----------------------
 
-Transfer and compile the Clipboard.Mod driver. This makes these commands
-available:
+## Clipboard integration
+
+The Clipboard module provides access to the host operating system's
+clipboard using these commands:
 
 * `Clipboard.Paste`
 * `Clipboard.CopySelection`
 * `Clipboard.CopyViewer`
 
 
-Known issues
-------------
+## Known issues
 
 * The wireless network interface is not emulated.
 * Proper documentation is needed.
 
 
-Copyright
----------
+## Copyright
 
 Copyright © 2014 Peter De Wachter