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

3 files changed, 49 insertions, 38 deletions

diff --git a/arch/mcu.h b/arch/mcu.h
index 5de6ea9..3b2b974 100644
--- a/arch/mcu.h
+++ b/arch/mcu.h
@@ -5,14 +5,18 @@
 
 // This helps abstract away the differences between various attiny MCUs.
 
-// Choose your MCU here, or in the main .c file, or in the build script
-//#define ATTINY 13
-//#define ATTINY 25
+// auto-detect eeprom size from avr-libc headers
+#ifndef EEPROM_SIZE
+    #ifdef E2SIZE
+        #define EEPROM_SIZE E2SIZE
+    #elif defined(E2END)
+        #define EEPROM_SIZE (E2END+1)
+    #endif
+#endif
 
 /******************** hardware-specific values **************************/
 #if (ATTINY == 13)
     #define F_CPU 4800000UL
-    //#define EEPSIZE 64
     #define V_REF REFS0
     #define BOGOMIPS 950
     #define ADMUX_VCC 0b00001100
@@ -22,7 +26,6 @@
 #elif (ATTINY == 25)
     // TODO: Use 6.4 MHz instead of 8 MHz?
     #define F_CPU 8000000UL
-    //#define EEPSIZE 128
     #define V_REF REFS1
     #define BOGOMIPS (F_CPU/4000)
     #define ADMUX_VCC 0b00001100
@@ -33,7 +36,6 @@
 #elif (ATTINY == 85)
     // TODO: Use 6.4 MHz instead of 8 MHz?
     #define F_CPU 8000000UL
-    //#define EEPSIZE 512
     #define V_REF REFS1
     #define BOGOMIPS (F_CPU/4000)
     // (1 << V_REF) | (0 << ADLAR) | (VCC_CHANNEL)
@@ -59,21 +61,11 @@
     #define AVRXMEGA3
     #define F_CPU 10000000UL
     #define BOGOMIPS (F_CPU/4700)
-    #define EEPSIZE 128
     #define DELAY_ZERO_TIME 1020
 #else
     #error Hey, you need to define ATTINY.
 #endif
 
-// auto-detect eeprom size from avr-libc headers
-#ifndef EEPSIZE
-#ifdef E2SIZE
-#define EEPSIZE E2SIZE
-#else
-#define EEPSIZE (E2END+1)
-#endif
-#endif
-
 
 #include <avr/interrupt.h>
 
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)])); }
+