made build fail if eeprom data bigger than MCU's eeprom size

Based on techniques suggested by DurvalMenezes here:
https://github.com/ToyKeeper/anduril/pull/4

2 files changed, 41 insertions, 22 deletions

diff --git a/fsm/eeprom.h b/fsm/eeprom.h
index 440d2b3..1e10fd2 100644
--- a/fsm/eeprom.h
+++ b/fsm/eeprom.h
@@ -7,44 +7,49 @@
 #include <avr/eeprom.h>
 
 // set this higher to enable normal eeprom functions
+// TODO: rename to EEPROM_BYTES_NEEDED or similar, to make purpose clearer
 #ifndef EEPROM_BYTES
 #define EEPROM_BYTES 0
 #endif
 
 // set this higher to enable wear-levelled eeprom functions
+// TODO: rename to EEPROM_WL_BYTES_NEEDED or similar, to make purpose clearer
 #ifndef EEPROM_WL_BYTES
 #define EEPROM_WL_BYTES 0
 #endif
 
 #ifdef USE_EEPROM
-// this fails when EEPROM_BYTES is a sizeof()
-//#if EEPROM_BYTES >= (EEPSIZE/2)
-//#error Requested EEPROM_BYTES too big.
-//#endif
-#ifdef EEPROM_OVERRIDE
-uint8_t *eeprom;
-#else
-uint8_t eeprom[EEPROM_BYTES];
-#endif
-uint8_t load_eeprom();  // returns 1 for success, 0 for no data found
-void save_eeprom();
-#define EEP_START (EEPSIZE/2)
+    #ifdef USE_EEPROM_WL
+        // split eeprom in half
+        #define EEP_START  (EEPROM_SIZE/2)
+        BUILD_ASSERT(eep_less_than_half, EEPROM_BYTES <= (EEPROM_SIZE/2));
+    #else
+        // use entire eeprom
+        #define EEP_START  0
+        BUILD_ASSERT(eep_data_fits, EEPROM_BYTES <= EEPROM_SIZE);
+    #endif
+    #ifdef EEPROM_OVERRIDE
+        uint8_t *eeprom;
+    #else
+        uint8_t eeprom[EEPROM_BYTES];
+    #endif
+    uint8_t load_eeprom();  // returns 1 for success, 0 for no data found
+    void save_eeprom();
 #endif
 
 #ifdef USE_EEPROM_WL
-#if EEPROM_WL_BYTES >= (EEPSIZE/4)
-#error Requested EEPROM_WL_BYTES too big.
-#endif
-uint8_t eeprom_wl[EEPROM_WL_BYTES];
-uint8_t load_eeprom_wl();  // returns 1 for success, 0 for no data found
-void save_eeprom_wl();
-#define EEP_WL_SIZE (EEPSIZE/2)
+    #define EEP_WL_SIZE (EEPROM_SIZE/2)
+    // ensure space for at least 2 slots for wear levelling
+    BUILD_ASSERT(eepwl_two_slots_minimum, EEPROM_WL_BYTES <= (EEP_WL_SIZE/2));
+    uint8_t eeprom_wl[EEPROM_WL_BYTES];
+    uint8_t load_eeprom_wl();  // returns 1 for success, 0 for no data found
+    void save_eeprom_wl();
 #endif
 
-#if EEPSIZE > 256
-#define EEP_OFFSET_T uint16_t
+#if EEPROM_SIZE > 256
+    #define EEP_OFFSET_T uint16_t
 #else
-#define EEP_OFFSET_T uint8_t
+    #define EEP_OFFSET_T uint8_t
 #endif
 
 // if this marker isn't found, the eeprom is assumed to be blank
diff --git a/fsm/tk.h b/fsm/tk.h
index 785808d..f2e7efe 100644
--- a/fsm/tk.h
+++ b/fsm/tk.h
@@ -24,3 +24,17 @@
 // use it like this:
 //#include incfile(CONFIGFILE)
 
+
+// cause a build failure if `condition` is true
+// (gcc compile trick taken from an old version of include/linux/kernel.h)
+// more info here:
+// https://scaryreasoner.wordpress.com/2009/02/28/checking-sizeof-at-compile-time/
+#define BUILD_FAIL_IF(name, condition)  \
+    __attribute__((unused)) static void name() \
+    { ((void)sizeof(char[1 - 2*!!(condition)])); }
+
+// cause a build failure if `condition` is false
+#define BUILD_ASSERT(name, condition)  \
+    __attribute__((unused)) static void name() \
+    { ((void)sizeof(char[1 - 2*!(condition)])); }
+