diff --git a/Makefile-ARM b/Makefile-ARM
index 8148d7b..b4bda7c 100644
--- a/Makefile-ARM
+++ b/Makefile-ARM
@@ -100,11 +100,11 @@ TARGET = $(PROGRAM).hex
 SOURCES  = mendel.c cpu.c serial.c sermsg.c sersendf.c delay.c
 SOURCES += gcode_parse.c gcode_process.c pinio.c timer.c clock.c
 SOURCES += dda_queue.c dda_maths.c dda_kinematics.c dda.c dda_lookahead.c
-SOURCES += analog.c temp.c heater.c home.c debug.c crc.c
-SOURCES += intercom.c graycode.c
+SOURCES += analog.c temp.c heater.c home.c debug.c crc.c pff.c pff_diskio.c
+SOURCES += spi.c intercom.c graycode.c
 # Sources left:
-# spi.c usb_serial.c
-# pff.c watchdog.c pff_diskio.c
+# usb_serial.c
+# watchdog.c
 
 ifeq ($(MCU), lpc1114)
   SOURCES += cmsis-system_lpc11xx.c
diff --git a/gcode_process.c b/gcode_process.c
index c533d03..b464ecc 100644
--- a/gcode_process.c
+++ b/gcode_process.c
@@ -374,7 +374,6 @@ void process_gcode_command() {
 				tool = next_tool;
 				break;
 
-      #ifndef __ARMEL_NOTYET__
       #ifdef SD
       case 20:
         //? --- M20: list SD card. ---
@@ -423,7 +422,6 @@ void process_gcode_command() {
         gcode_sources &= ! GCODE_SOURCE_SD;
         break;
       #endif /* SD */
-      #endif /* __ARMEL_NOTYET__ */
 
 			case 82:
 				//? --- M82 - Set E codes absolute ---
diff --git a/mendel.c b/mendel.c
index 9e8966f..e8d4feb 100644
--- a/mendel.c
+++ b/mendel.c
@@ -35,16 +35,13 @@
 #include	"gcode_parse.h"
 #include	"timer.h"
 #include	"temp.h"
-#ifndef __ARMEL_NOTYET__
 #include	"watchdog.h"
-#endif /* __ARMEL_NOTYET__ */
 #include	"debug.h"
 #include	"heater.h"
 #include	"analog.h"
 #include	"pinio.h"
 #include	"clock.h"
 #include	"intercom.h"
-#ifndef __ARMEL_NOTYET__
 #include "spi.h"
 #include "sd.h"
 #include "simulator.h"
@@ -59,6 +56,7 @@
   #endif
 #endif
 
+#ifndef __ARMEL_NOTYET__
 #ifdef CANNED_CYCLE
   const char PROGMEM canned_gcode_P[] = CANNED_CYCLE;
 #endif
@@ -74,10 +72,8 @@ void init(void) {
 
   cpu_init();
 
-  #ifndef __ARMEL_NOTYET__
 	// set up watchdog
 	wd_init();
-  #endif /* __ARMEL_NOTYET__ */
 
 	// set up serial
 	serial_init();
@@ -88,11 +84,9 @@ void init(void) {
 	// set up inputs and outputs
   pinio_init();
 
-  #ifndef __ARMEL_NOTYET__
-  #if defined SPI
+  #ifdef SPI
     spi_init();
   #endif
-  #endif /* __ARMEL_NOTYET__ */
 
 	// set up timers
 	timer_init();
@@ -109,19 +103,15 @@ void init(void) {
 	// set up temperature inputs
 	temp_init();
 
-  #ifndef __ARMEL_NOTYET__
   #ifdef SD
     sd_init();
   #endif
-  #endif /* __ARMEL_NOTYET__ */
 
 	// enable interrupts
 	sei();
 
-  #ifndef __ARMEL_NOTYET__
 	// reset watchdog
 	wd_reset();
-  #endif /* __ARMEL_NOTYET__ */
 
   // prepare the power supply
   power_init();
@@ -180,7 +170,6 @@ int main (void)
         }
       }
 
-    #ifndef __ARMEL_NOTYET__
       #ifdef SD
         if (( ! gcode_active || gcode_active & GCODE_SOURCE_SD) &&
             gcode_sources & GCODE_SOURCE_SD) {
@@ -193,6 +182,7 @@ int main (void)
         }
       #endif
 
+      #ifndef __ARMEL_NOTYET__
       #ifdef CANNED_CYCLE
         /**
           WARNING!
diff --git a/sd.h b/sd.h
index fe4f048..92a0229 100644
--- a/sd.h
+++ b/sd.h
@@ -14,6 +14,13 @@
 
 // Feature set of Petit FatFs is currently defined early in pff_conf.h.
 
+/**
+  Test configuration.
+*/
+#ifdef __ARMEL__
+  #error SD card (SD_CARD_SELECT_PIN) not yet supported on ARM.
+#endif
+
 
 void sd_init(void);
 
diff --git a/spi.c b/spi.c
index 8ba46f5..e1f1fdd 100644
--- a/spi.c
+++ b/spi.c
@@ -15,7 +15,7 @@
 
 #ifdef SPI
 
-/** Initialise serial subsystem.
+/** Initialise SPI subsystem.
 
   Code copied from ATmega164/324/644/1284 data sheet, section 18.2, page 160,
   or moved here from mendel.c.
diff --git a/spi.h b/spi.h
index 73c4a57..c5258f4 100644
--- a/spi.h
+++ b/spi.h
@@ -7,10 +7,16 @@
 
 #ifdef SPI
 
+/**
+  Test configuration.
+*/
+#ifdef __ARMEL__
+  #error SPI (SD_CARD_SELECT_PIN, TEMP_MAX6675) not yet supported on ARM.
+#endif
+
 // Uncomment this to double SPI frequency from (F_CPU / 4) to (F_CPU / 2).
 //#define SPI_2X
 
-
 /** Initialise SPI subsystem.
 */
 void spi_init(void);
diff --git a/temp.c b/temp.c
index 160ec20..912506d 100644
--- a/temp.c
+++ b/temp.c
@@ -20,11 +20,17 @@
 #include "simulator.h"
 
 #ifdef	TEMP_INTERCOM
+  #ifdef __ARMEL__
+    #error TEMP_INTERCOM not yet supported on ARM.
+  #endif
 	#include	"intercom.h"
   #include "pinio.h"
 #endif
 
 #ifdef	TEMP_MAX6675
+  #ifdef __ARMEL__
+    #error MAX6675 sensors (TEMP_MAX6675) not yet supported on ARM.
+  #endif
   #include "spi.h"
 #endif