+The code on the device generates the specification. When a device does not have
+a specific peripheral, the code will also not be on the device. In the
+interface file, the code for peripherals is always guarded by macros. Thus, if
+the peripheral is not there, the macro is set accordingly and the code will not
+be included. To illustrate this, Listings~\ref{lst:macro}-\ref{lst:macro3}
+show parts of the interface file and device specification generation function
+for the \emph{NodeMCU} microcontroller which only boasts a single analog pin
+and eight digital pins.
+
+\begin{minipage}{.49\textwidth}
+ \begin{lstlisting}[label={lst:macro},language=C,%
+ caption={Specification in the interface}]
+...
+#elif defined ARDUINO_ESP8266_NODEMCU
+#define APINS 1
+#define DPINS 8
+#define STACKSIZE 1024
+#define MEMSIZE 1024
+#define HAVELED 0
+#define HAVEHB 0
+
+#if APINS > 0
+void write_apin(uint8_t p, uint8_t v);
+uint8_t read_apin(uint8_t pin);
+#endif
+ \end{lstlisting}
+\end{minipage}
+\begin{minipage}{.49\textwidth}
+ \begin{lstlisting}[label={lst:macro3},language=C,%
+ caption={Actual generation}]
+...
+void spec_send(void) {
+ write_byte('c');
+ write_byte(0 | (HAVELED << 0)
+ | (HAVELCD << 1)
+ | (HAVEHB << 2)
+ | ...);
+ write16(MEMSIZE);
+ write16(STACKSIZE);
+ write_byte(APINS);
+ write_byte(DPINS);
+ write_byte('\n');
+}
+ \end{lstlisting}
+\end{minipage}
+