To compile on Mac OS X 10.12.4 and installing libffi with homebrew 1.1.13-142-g539881f51a, I had to specify the PKG_CONFIG_PATH variable manually.

Micro-Python-on-Mac-OSX.md

@@ -21,6 +21,11 @@ In order to compile on OSX you will need the following software packages install
 ## Build Process
 Same as on Linux - go to `micropython/unix` and run `make` (or `make -B` or `make clean; make` if rebuilding.
 
+If installing libffi with homebrew, you might have to specify its location to pkgconfig
+```
+export PKG_CONFIG_PATH=/usr/local/Cellar/libffi/3.2.1/lib/pkgconfig/
+```
+
 ## Running tests
 Go to `micropython/tests` and run the test script `./run-tests`
 The test script will look for the executable in `../unix/micropython` and will compare the output of the micropython executable to the locally installed version of Python3