README.md: update with information about compilation and installation

README.md

@@ -39,9 +39,10 @@ results in a binary size of 118220 bytes. Huge. The same thing compiled with lib
 ```
 m68k-atari-mint-gcc -nostdlib $LIBCMINI/crt0.o hello.c -o hello.tos -s -L$LIBCMINI -lcmini -lgcc
 ```
-(note that - since we compile with -nostdlib - you have to add the gcc runtime support library libgcc.a to your command line for the processors that need it)
+(note that - since we compile with -nostdlib - you have to add the gcc runtime support library libgcc.a to your command line for the processors that need it.
+Sometimes you will have to specify ` -lgcc -lcmini -lgcc` to avoid 'undefined reference' error messages.)
 
-creates a binary with 11794 byts. About a tenth of the size.
+creates a binary with 11794 bytes. About a tenth of the size.
 
 Remember that gcc does not automatically look up multi-lib versions of
 libraries in directories specified by -L. If you want to do the same as
@@ -81,6 +82,64 @@ avoid library calls for most integer operations.
 
 With -mfastcall libcmini itself is 3% smaller binary, and the tests/bench test executes 20% faster. 
 
+## Compilation
+
+The library can be compiled in standard ('a.out') or `elf' format. In the first case the m68k-atari-mint toolchain is used; in the latter case the m68k-atari-mintelf toolchain. Make sure the proper toolchain is in your PATH before compiling.
+
+The basic command for compilation is `make`. But various compilation options can be given.
+Instead of 'Y', also 'yes' can be used:
+
+  * `VERBOSE=Y` - Print all commands that are used to compile the library. This option can also be given as an environment variable. All other options must be given as arguments to the `make` command.
+  * `COMPILE_ELF=Y` - Compile for 'elf' format instead of 'a.out'.
+  * `ONLY_68K=Y` - Compile only for the 68000, not the other architectures.
+  * `COMPILE_ELF=Y` - Compile for the 'elf' format instead of 'a.out'.
+  * `STDIO_WITH_LONG_LONG=Y` - Add code for `long long` to the `printf` family of functions. At the moment this fails.
+  * `STDIO_MAP_NEWLINE=Y` - Add code to convert NL to CR NL on output to text files, and CR NL to NL on input. This was standard practice on TOS but not on Mint.
+
+The following options are on by default. They can be switched off with `OPTION=no` or `OPTION=N`.
+However, when `ONLY_68K=Y` is given, they are switched off and cannot be switched on again.
+
+  * `BUILD_CF=N` - Don't compile for the Coldfire (m5475) architecture.
+  * `BUILD_SOFT_FLOAT=N` - Not sure what this means. Probably don't build for software floating point.
+  * `BUILD_SHORT=N` - Don't include libraries for short ints (16 bit?)
+  * `BUILD_FAST=N` - Don't use `-mfastcall` function calls. The default for this option is whether the compiler supports `-mfastcall`.
+
+Example `make` command:
+
+```
+VERBOSE=yes make ONLY_68K=yes STDIO_MAP_NEWLINE=Y
+```
+
+## Installation
+
+The basic installation command is `make install`. The default install
+location is `/usr`, i.e. `/usr/include` and `/usr/lib`. `make install`
+should basically get the same options as used for the compilation if
+some architectures were omitted, otherwise it will regenerate the
+missing ones.
+
+The installation destination can be specified with either the `PREFIX*` options or the `DESTDIR` option:
+  * `PREFIX=<dir>` - Install in `$PREFIX/include` and `$PREFIX/lib`, unless one or more of the following options are given:
+  * `PREFIX_FOR_INCLUDE=<dir>` - Directory for the include files. When multiple architectures are present,
+only one copy of the include files are installed. Default is `$PREFIX/include`.
+  * `PREFIX_FOR_LIB=<dir>` - Directory for the library files. Default is `$PREFIX/lib`.
+  * `PREFIX_FOR_STARTUP=<dir>` - Directory for the startup file (`crt0.o`). Default is `$PREFIX/lib`.
+  * `DESTDIR=<dir` - Installs the include files in `$(DESTDIR)/usr/include` and the library and startup file in
+    `$(DESTDIR)/usr/lib`.
+
+The `DESTDIR` and `PREFIX*` options cannot be used together. They can also be given as environment variables.
+
+If the library has been built for multiple architectures, there will be
+a subdirectory for each one (except the basic 68000) in the library
+directory. For the `elf` version, this applies also to the startup file.
+
+Example `make install` command corresponding to the above compile command:
+
+```
+VERBOSE=yes make ONLY_68K=yes PREFIX=/opt/libcmini install
+```
+The `STDIO_MAP_NEWLINE` option is only relevant at compile time, so this was left out.
+
 ## Contribution
 
 Contributions are always welcome.