Introduce #ifdef SPI.

It's better to separate this by function than by usage.

config_wrapper.h

@@ -34,6 +34,13 @@
   #undef BAUD
 #endif
 
+/**
+  Check wether we need SPI.
+*/
+#if (defined SD_CARD_SELECT_PIN || defined TEMP_MAX6675) && ! defined SIMULATOR
+  #define SPI
+#endif
+
 /**
   ACCELERATION_TEMPORAL doesn't support lookahead, yet.
 */

cpu-avr.c

@@ -18,13 +18,13 @@
 */
 void cpu_init() {
   #ifdef PRR
-    #if defined TEMP_MAX6675 || defined SD
+    #if defined SPI
       PRR = MASK(PRTWI) | MASK(PRADC);
     #else
       PRR = MASK(PRTWI) | MASK(PRADC) | MASK(PRSPI);
     #endif
   #elif defined PRR0
-    #if defined TEMP_MAX6675 || defined SD
+    #if defined SPI
       PRR0 = MASK(PRTWI) | MASK(PRADC);
     #else
       PRR0 = MASK(PRTWI) | MASK(PRADC) | MASK(PRSPI);

mendel.c

@@ -89,7 +89,7 @@ void init(void) {
   pinio_init();
 
   #ifndef __ARMEL_NOTYET__
-  #if defined TEMP_MAX6675 || defined SD
+  #if defined SPI
     spi_init();
   #endif
   #endif /* __ARMEL_NOTYET__ */

simulator/spi_sim.c

@@ -5,5 +5,9 @@
 #include "spi.h"
 #include "arduino.h"
 
+#ifdef SPI
+
 void spi_init() {
 }
+
+#endif /* SPI */

spi.c

@@ -13,9 +13,7 @@
 */
 #include "spi.h"
 
-#include "arduino.h"
-#include "pinio.h"
-
+#ifdef SPI
 
 /** Initialise serial subsystem.
 
@@ -44,3 +42,5 @@ void spi_init() {
   // This sets the whole SPRC register.
   spi_speed_100_400();
 }
+
+#endif /* SPI */

spi.h

@@ -5,6 +5,8 @@
 #include "arduino.h"
 #include "pinio.h"
 
+#ifdef SPI
+
 // Uncomment this to double SPI frequency from (F_CPU / 4) to (F_CPU / 2).
 //#define SPI_2X
 
@@ -13,8 +15,6 @@
 */
 void spi_init(void);
 
-#ifndef SIMULATOR /* Avoid inlining code on simulator. */
-
 /** SPI device selection.
 
   Because out famous WRITE() macro works with constant pins, only, we define
@@ -102,5 +102,6 @@ inline uint8_t spi_rw(uint8_t byte) {
   return SPDR;
 }
 
-#endif /* SIMULATOR */
+#endif /* SPI */
+
 #endif /* _SPI_H */