doc/ccache: move to “Advanced build system tricks”

doc/doxygen/riot.doxyfile

@@ -878,7 +878,6 @@ INPUT                  = ../../doc.txt \
                          src/build-in-docker.md \
                          ../../tests/README.md \
                          src/dev-best-practices.md \
-                         src/ccache.md \
                          src/comparing-build-sizes.md \
                          src/static-vs-dynamic-memory.md \
                          src/build-system-basics.md \

doc/doxygen/src/advanced-build-system-tricks.md

@@ -39,6 +39,87 @@ You can configure your own files that will be parsed by the build system main
 * Define your custom targets
 * Override default targets
 
+Speed-up builds with ccache                                           {#ccache}
+===========================
+
+[`ccache`](https://ccache.samba.org/) is a compiler cache. It speeds up recompilation by caching previous compilations and detecting when the same compilation is being done again.
+
+Usually, the initial build takes a little (5% - 20%) longer, but repeated builds are up to ten times faster.
+Using `ccache` is safe, as `ccache` tries very hard to not mess up things and falls back to a normal compile if it cannot ensure correct output.
+
+There's one drawback: without further tweaking, `gcc` stops emitting colored output.
+
+Setup
+-----
+
+- Install using the package manager of your distribution, e.g., on Ubuntu or Debian:
+
+~~~~~~~~~~~~~~~~~~~
+# sudo apt-get install ccache
+~~~~~~~~~~~~~~~~~~~
+
+- Set `CCACHE` variable to `ccache`:
+
+~~~~~~~~~~~~~~~~~~~
+# export CCACHE=ccache
+~~~~~~~~~~~~~~~~~~~
+
+- (Optionally) add the above export line to your `~/.profile`
+
+Result
+------
+
+Build without `ccache`:
+
+~~~~~~~~~~~~~~~~~~~
+[kaspar@booze default (master)]$ time BOARD=samr21-xpro make clean all
+Building application "default" for "samr21-xpro" with MCU "samd21".
+
+[...]
+
+   text    data     bss     dec     hex filename
+  37016     180    6008   43204    a8c4 /home/kaspar/src/riot/examples/default/bin/samr21-xpro/default.elf
+
+real    0m12.321s
+user    0m10.317s
+sys     0m1.170s
+[kaspar@booze default (master)]$
+~~~~~~~~~~~~~~~~~~~
+
+First build with `ccache` enabled:
+
+~~~~~~~~~~~~~~~~~~~
+[kaspar@booze default (master)]$ time BOARD=samr21-xpro make clean all
+Building application "default" for "samr21-xpro" with MCU "samd21".
+
+[...]
+
+text    data     bss     dec     hex filename
+37016     180    6008   43204    a8c4 /home/kaspar/src/riot/examples/default/bin/samr21-xpro/default.elf
+
+real    0m15.462s
+user    0m12.410s
+sys     0m1.597s
+[kaspar@booze default (master)]$
+~~~~~~~~~~~~~~~~~~~
+
+Subsequent build with `ccache` enabled:
+
+~~~~~~~~~~~~~~~~~~~
+[kaspar@booze default (master)]$ time BOARD=samr21-xpro make clean all
+Building application "default" for "samr21-xpro" with MCU "samd21".
+
+[...]
+
+   text    data     bss     dec     hex filename
+  37016     180    6008   43204    a8c4 /home/kaspar/src/riot/examples/default/bin/samr21-xpro/default.elf
+
+real    0m2.157s
+user    0m1.213s
+sys     0m0.327s
+[kaspar@booze default (master)]$
+~~~~~~~~~~~~~~~~~~~
+
 Analyze dependency resolution                   {#analyze-depedency-resolution}
 =============================