Setting up Your Machine
The code generation is handled completely within the Wolfram System. However, to compile and download the code it invokes an external toolchain.
If you are working with a microcontroller on an Arduino board, MicrocontrollerEmbedCode looks for the Arduino IDE. To see if the compiler and other programs can be successfully invoked run a test to blink the LED on the board. For example, if you have an Arduino Uno run the following code after modifying the last argument to match the connection port of your machine.
If the LED is blinking every second then the Arduino toolchain is being correctly invoked. If not, it must be explicitly specified.
If an avr-gcc toolchain has been installed elsewhere, that can be used as well.
The path "/usr/local/bin" is in the system path.
If it is in the system path, the path need not be explicitly given.