eeprom_stm32: implement high density wear leveling (#12567)

* eeprom_stm32: implement wear leveling
Update EECONFIG_MAGIC_NUMBER
eeprom_stm32: check emulated eeprom size is large enough
* eeprom_stm32: Increasing simulated EEPROM density on stm32
* Adding utility script to decode emulated eeprom
* Adding unit tests
* Applying qmk cformat changes
* cleaned up flash mocking
* Fix for stm32eeprom_parser.py checking via signature with wrong base
* Fix for nk65 keyboard

Co-authored-by: Ilya Zhuravlev <whatever@xyz.is>
Co-authored-by: zvecr <git@zvecr.com>

7 files changed, 1206 insertions, 176 deletions

diff --git a/tmk_core/common/chibios/eeprom_stm32.c b/tmk_core/common/chibios/eeprom_stm32.c
index ea51989728..5bf852fde1 100644
--- a/tmk_core/common/chibios/eeprom_stm32.c
+++ b/tmk_core/common/chibios/eeprom_stm32.c
@@ -14,185 +14,751 @@
  * Artur F.
  *
  * Modifications for QMK and STM32F303 by Yiancar
+ * Modifications to add flash wear leveling by Ilya Zhuravlev
+ * Modifications to increase flash density by Don Kjer
  */
 
 #include <stdio.h>
-#include <string.h>
+#include <stdbool.h>
+#include "debug.h"
 #include "eeprom_stm32.h"
-/*****************************************************************************
- * Allows to use the internal flash to store non volatile data. To initialize
- * the functionality use the EEPROM_Init() function. Be sure that by reprogramming
- * of the controller just affected pages will be deleted. In other case the non
- * volatile data will be lost.
- ******************************************************************************/
+#include "flash_stm32.h"
+
+/*
+ * We emulate eeprom by writing a snapshot compacted view of eeprom contents,
+ * followed by a write log of any change since that snapshot:
+ *
+ * === SIMULATED EEPROM CONTENTS ===
+ *
+ * ┌─ Compacted ┬ Write Log ─┐
+ * │............│[BYTE][BYTE]│
+ * │FFFF....FFFF│[WRD0][WRD1]│
+ * │FFFFFFFFFFFF│[WORD][NEXT]│
+ * │....FFFFFFFF│[BYTE][WRD0]│
+ * ├────────────┼────────────┤
+ * └──PAGE_BASE │            │
+ *    PAGE_LAST─┴─WRITE_BASE │
+ *                WRITE_LAST ┘
+ *
+ * Compacted contents are the 1's complement of the actual EEPROM contents.
+ * e.g. An 'FFFF' represents a '0000' value.
+ *
+ * The size of the 'compacted' area is equal to the size of the 'emulated' eeprom.
+ * The size of the compacted-area and write log are configurable, and the combined
+ * size of Compacted + WriteLog is a multiple FEE_PAGE_SIZE, which is MCU dependent.
+ * Simulated Eeprom contents are located at the end of available flash space.
+ *
+ * The following configuration defines can be set:
+ *
+ * FEE_DENSITY_PAGES   # Total number of pages to use for eeprom simulation (Compact + Write log)
+ * FEE_DENSITY_BYTES   # Size of simulated eeprom. (Defaults to half the space allocated by FEE_DENSITY_PAGES)
+ * NOTE: The current implementation does not include page swapping,
+ * and FEE_DENSITY_BYTES will consume that amount of RAM as a cached view of actual EEPROM contents.
+ *
+ * The maximum size of FEE_DENSITY_BYTES is currently 16384. The write log size equals
+ * FEE_DENSITY_PAGES * FEE_PAGE_SIZE - FEE_DENSITY_BYTES.
+ * The larger the write log, the less frequently the compacted area needs to be rewritten.
+ *
+ *
+ * *** General Algorithm ***
+ *
+ * During initialization:
+ * The contents of the Compacted-flash area are loaded and the 1's complement value
+ * is cached into memory (e.g. 0xFFFF in Flash represents 0x0000 in cache).
+ * Write log entries are processed until a 0xFFFF is reached.
+ * Each log entry updates a byte or word in the cache.
+ *
+ * During reads:
+ * EEPROM contents are given back directly from the cache in memory.
+ *
+ * During writes:
+ * The contents of the cache is updated first.
+ * If the Compacted-flash area corresponding to the write address is unprogrammed, the 1's complement of the value is written directly into Compacted-flash
+ * Otherwise:
+ * If the write log is full, erase both the Compacted-flash area and the Write log, then write cached contents to the Compacted-flash area.
+ * Otherwise a Write log entry is constructed and appended to the next free position in the Write log.
+ *
+ *
+ * *** Write Log Structure ***
+ *
+ * Write log entries allow for optimized byte writes to addresses below 128. Writing 0 or 1 words are also optimized when word-aligned.
+ *
+ * === WRITE LOG ENTRY FORMATS ===
+ *
+ * ╔═══ Byte-Entry ══╗
+ * ║0XXXXXXX║YYYYYYYY║
+ * ║ └──┬──┘║└──┬───┘║
+ * ║ Address║ Value  ║
+ * ╚════════╩════════╝
+ * 0 <= Address < 0x80 (128)
+ *
+ * ╔ Word-Encoded 0 ╗
+ * ║100XXXXXXXXXXXXX║
+ * ║  │└─────┬─────┘║
+ * ║  │Address >> 1 ║
+ * ║  └── Value: 0  ║
+ * ╚════════════════╝
+ * 0 <= Address <= 0x3FFE (16382)
+ *
+ * ╔ Word-Encoded 1 ╗
+ * ║101XXXXXXXXXXXXX║
+ * ║  │└─────┬─────┘║
+ * ║  │Address >> 1 ║
+ * ║  └── Value: 1  ║
+ * ╚════════════════╝
+ * 0 <= Address <= 0x3FFE (16382)
+ *
+ * ╔═══ Reserved ═══╗
+ * ║110XXXXXXXXXXXXX║
+ * ╚════════════════╝
+ *
+ * ╔═══════════ Word-Next ═══════════╗
+ * ║111XXXXXXXXXXXXX║YYYYYYYYYYYYYYYY║
+ * ║   └─────┬─────┘║└───────┬──────┘║
+ * ║(Address-128)>>1║     ~Value     ║
+ * ╚════════════════╩════════════════╝
+ * (  0 <= Address <  0x0080 (128): Reserved)
+ * 0x80 <= Address <= 0x3FFE (16382)
+ *
+ * Write Log entry ranges:
+ * 0x0000 ... 0x7FFF - Byte-Entry;     address is (Entry & 0x7F00) >> 4; value is (Entry & 0xFF)
+ * 0x8000 ... 0x9FFF - Word-Encoded 0; address is (Entry & 0x1FFF) << 1; value is 0
+ * 0xA000 ... 0xBFFF - Word-Encoded 1; address is (Entry & 0x1FFF) << 1; value is 1
+ * 0xC000 ... 0xDFFF - Reserved
+ * 0xE000 ... 0xFFBF - Word-Next;      address is (Entry & 0x1FFF) << 1 + 0x80; value is ~(Next_Entry)
+ * 0xFFC0 ... 0xFFFE - Reserved
+ * 0xFFFF            - Unprogrammed
+ *
+ */
 
-/* Private macro -------------------------------------------------------------*/
-/* Private variables ---------------------------------------------------------*/
-/* Functions -----------------------------------------------------------------*/
+/* These bits are used for optimizing encoding of bytes, 0 and 1 */
+#define FEE_WORD_ENCODING 0x8000
+#define FEE_VALUE_NEXT 0x6000
+#define FEE_VALUE_RESERVED 0x4000
+#define FEE_VALUE_ENCODED 0x2000
+#define FEE_BYTE_RANGE 0x80
+
+// HACK ALERT. This definition may not match your processor
+// To Do. Work out correct value for EEPROM_PAGE_SIZE on the STM32F103CT6 etc
+#if defined(EEPROM_EMU_STM32F303xC)
+#    define MCU_STM32F303CC
+#elif defined(EEPROM_EMU_STM32F103xB)
+#    define MCU_STM32F103RB
+#elif defined(EEPROM_EMU_STM32F072xB)
+#    define MCU_STM32F072CB
+#elif defined(EEPROM_EMU_STM32F042x6)
+#    define MCU_STM32F042K6
+#elif !defined(FEE_PAGE_SIZE) || !defined(FEE_DENSITY_PAGES) || !defined(FEE_MCU_FLASH_SIZE)
+#    error "not implemented."
+#endif
+
+#if !defined(FEE_PAGE_SIZE) || !defined(FEE_DENSITY_PAGES)
+#    if defined(MCU_STM32F103RB) || defined(MCU_STM32F042K6)
+#        ifndef FEE_PAGE_SIZE
+#            define FEE_PAGE_SIZE 0x400  // Page size = 1KByte
+#        endif
+#        ifndef FEE_DENSITY_PAGES
+#            define FEE_DENSITY_PAGES 2  // How many pages are used
+#        endif
+#    elif defined(MCU_STM32F103ZE) || defined(MCU_STM32F103RE) || defined(MCU_STM32F103RD) || defined(MCU_STM32F303CC) || defined(MCU_STM32F072CB)
+#        ifndef FEE_PAGE_SIZE
+#            define FEE_PAGE_SIZE 0x800  // Page size = 2KByte
+#        endif
+#        ifndef FEE_DENSITY_PAGES
+#            define FEE_DENSITY_PAGES 4  // How many pages are used
+#        endif
+#    else
+#        error "No MCU type specified. Add something like -DMCU_STM32F103RB to your compiler arguments (probably in a Makefile)."
+#    endif
+#endif
+
+#ifndef FEE_MCU_FLASH_SIZE
+#    if defined(MCU_STM32F103RB) || defined(MCU_STM32F072CB)
+#        define FEE_MCU_FLASH_SIZE 128  // Size in Kb
+#    elif defined(MCU_STM32F042K6)
+#        define FEE_MCU_FLASH_SIZE 32  // Size in Kb
+#    elif defined(MCU_STM32F103ZE) || defined(MCU_STM32F103RE)
+#        define FEE_MCU_FLASH_SIZE 512  // Size in Kb
+#    elif defined(MCU_STM32F103RD)
+#        define FEE_MCU_FLASH_SIZE 384  // Size in Kb
+#    elif defined(MCU_STM32F303CC)
+#        define FEE_MCU_FLASH_SIZE 256  // Size in Kb
+#    else
+#        error "No MCU type specified. Add something like -DMCU_STM32F103RB to your compiler arguments (probably in a Makefile)."
+#    endif
+#endif
+
+#define FEE_XSTR(x) FEE_STR(x)
+#define FEE_STR(x) #x
+
+/* Size of combined compacted eeprom and write log pages */
+#define FEE_DENSITY_MAX_SIZE (FEE_DENSITY_PAGES * FEE_PAGE_SIZE)
+/* Addressable range 16KByte: 0 <-> (0x1FFF << 1) */
+#define FEE_ADDRESS_MAX_SIZE 0x4000
+
+#ifndef EEPROM_START_ADDRESS /* *TODO: Get rid of this check */
+#    if FEE_DENSITY_MAX_SIZE > (FEE_MCU_FLASH_SIZE * 1024)
+#        pragma message FEE_XSTR(FEE_DENSITY_MAX_SIZE) " > " FEE_XSTR(FEE_MCU_FLASH_SIZE * 1024)
+#        error emulated eeprom: FEE_DENSITY_PAGES is greater than available flash size
+#    endif
+#endif
+
+/* Size of emulated eeprom */
+#ifdef FEE_DENSITY_BYTES
+#    if (FEE_DENSITY_BYTES > FEE_DENSITY_MAX_SIZE)
+#        pragma message FEE_XSTR(FEE_DENSITY_BYTES) " > " FEE_XSTR(FEE_DENSITY_MAX_SIZE)
+#        error emulated eeprom: FEE_DENSITY_BYTES exceeds FEE_DENSITY_MAX_SIZE
+#    endif
+#    if (FEE_DENSITY_BYTES == FEE_DENSITY_MAX_SIZE)
+#        pragma message FEE_XSTR(FEE_DENSITY_BYTES) " == " FEE_XSTR(FEE_DENSITY_MAX_SIZE)
+#        warning emulated eeprom: FEE_DENSITY_BYTES leaves no room for a write log.  This will greatly increase the flash wear rate!
+#    endif
+#    if FEE_DENSITY_BYTES > FEE_ADDRESS_MAX_SIZE
+#        pragma message FEE_XSTR(FEE_DENSITY_BYTES) " > " FEE_XSTR(FEE_ADDRESS_MAX_SIZE)
+#        error emulated eeprom: FEE_DENSITY_BYTES is greater than FEE_ADDRESS_MAX_SIZE allows
+#    endif
+#    if ((FEE_DENSITY_BYTES) % 2) == 1
+#        error emulated eeprom: FEE_DENSITY_BYTES must be even
+#    endif
+#else
+/* Default to half of allocated space used for emulated eeprom, half for write log */
+#    define FEE_DENSITY_BYTES (FEE_DENSITY_PAGES * FEE_PAGE_SIZE / 2)
+#endif
+
+/* Size of write log */
+#define FEE_WRITE_LOG_BYTES (FEE_DENSITY_PAGES * FEE_PAGE_SIZE - FEE_DENSITY_BYTES)
+
+/* Start of the emulated eeprom compacted flash area */
+#ifndef FEE_FLASH_BASE
+#    define FEE_FLASH_BASE 0x8000000
+#endif
+#define FEE_PAGE_BASE_ADDRESS ((uintptr_t)(FEE_FLASH_BASE) + FEE_MCU_FLASH_SIZE * 1024 - FEE_WRITE_LOG_BYTES - FEE_DENSITY_BYTES)
+/* End of the emulated eeprom compacted flash area */
+#define FEE_PAGE_LAST_ADDRESS (FEE_PAGE_BASE_ADDRESS + FEE_DENSITY_BYTES)
+/* Start of the emulated eeprom write log */
+#define FEE_WRITE_LOG_BASE_ADDRESS FEE_PAGE_LAST_ADDRESS
+/* End of the emulated eeprom write log */
+#define FEE_WRITE_LOG_LAST_ADDRESS (FEE_WRITE_LOG_BASE_ADDRESS + FEE_WRITE_LOG_BYTES)
+
+/* Flash word value after erase */
+#define FEE_EMPTY_WORD ((uint16_t)0xFFFF)
+
+#if defined(DYNAMIC_KEYMAP_EEPROM_MAX_ADDR) && (DYNAMIC_KEYMAP_EEPROM_MAX_ADDR >= FEE_DENSITY_BYTES)
+#    error emulated eeprom: DYNAMIC_KEYMAP_EEPROM_MAX_ADDR is greater than the FEE_DENSITY_BYTES available
+#endif
+
+/* In-memory contents of emulated eeprom for faster access */
+/* *TODO: Implement page swapping */
+static uint16_t WordBuf[FEE_DENSITY_BYTES / 2];
+static uint8_t *DataBuf = (uint8_t *)WordBuf;
+
+/* Pointer to the first available slot within the write log */
+static uint16_t *empty_slot;
+
+// #define DEBUG_EEPROM_OUTPUT
+
+/*
+ * Debug print utils
+ */
+
+#if defined(DEBUG_EEPROM_OUTPUT)
+
+#    define debug_eeprom debug_enable
+#    define eeprom_println(s) println(s)
+#    define eeprom_printf(fmt, ...) xprintf(fmt, ##__VA_ARGS__);
+
+#else /* NO_DEBUG */
+
+#    define debug_eeprom false
+#    define eeprom_println(s)
+#    define eeprom_printf(fmt, ...)
+
+#endif /* NO_DEBUG */
+
+void print_eeprom(void) {
+#ifndef NO_DEBUG
+    int empty_rows = 0;
+    for (uint16_t i = 0; i < FEE_DENSITY_BYTES; i++) {
+        if (i % 16 == 0) {
+            if (i >= FEE_DENSITY_BYTES - 16) {
+                /* Make sure we display the last row */
+                empty_rows = 0;
+            }
+            /* Check if this row is uninitialized */
+            ++empty_rows;
+            for (uint16_t j = 0; j < 16; j++) {
+                if (DataBuf[i + j]) {
+                    empty_rows = 0;
+                    break;
+                }
+            }
+            if (empty_rows > 1) {
+                /* Repeat empty row */
+                if (empty_rows == 2) {
+                    /* Only display the first repeat empty row */
+                    println("*");
+                }
+                i += 15;
+                continue;
+            }
+            xprintf("%04x", i);
+        }
+        if (i % 8 == 0) print(" ");
+
+        xprintf(" %02x", DataBuf[i]);
+        if ((i + 1) % 16 == 0) {
+            println("");
+        }
+    }
+#endif
+}
 
-uint8_t DataBuf[FEE_PAGE_SIZE];
-/*****************************************************************************
- *  Delete Flash Space used for user Data, deletes the whole space between
- *  RW_PAGE_BASE_ADDRESS and the last uC Flash Page
- ******************************************************************************/
 uint16_t EEPROM_Init(void) {
-    // unlock flash
-    FLASH_Unlock();
+    /* Load emulated eeprom contents from compacted flash into memory */
+    uint16_t *src  = (uint16_t *)FEE_PAGE_BASE_ADDRESS;
+    uint16_t *dest = (uint16_t *)DataBuf;
+    for (; src < (uint16_t *)FEE_PAGE_LAST_ADDRESS; ++src, ++dest) {
+        *dest = ~*src;
+    }
+
+    if (debug_eeprom) {
+        println("EEPROM_Init Compacted Pages:");
+        print_eeprom();
+        println("EEPROM_Init Write Log:");
+    }
+
+    /* Replay write log */
+    uint16_t *log_addr;
+    for (log_addr = (uint16_t *)FEE_WRITE_LOG_BASE_ADDRESS; log_addr < (uint16_t *)FEE_WRITE_LOG_LAST_ADDRESS; ++log_addr) {
+        uint16_t address = *log_addr;
+        if (address == FEE_EMPTY_WORD) {
+            break;
+        }
+        /* Check for lowest 128-bytes optimization */
+        if (!(address & FEE_WORD_ENCODING)) {
+            uint8_t bvalue = (uint8_t)address;
+            address >>= 8;
+            DataBuf[address] = bvalue;
+            eeprom_printf("DataBuf[0x%02x] = 0x%02x;\n", address, bvalue);
+        } else {
+            uint16_t wvalue;
+            /* Check if value is in next word */
+            if ((address & FEE_VALUE_NEXT) == FEE_VALUE_NEXT) {
+                /* Read value from next word */
+                if (++log_addr >= (uint16_t *)FEE_WRITE_LOG_LAST_ADDRESS) {
+                    break;
+                }
+                wvalue = ~*log_addr;
+                if (!wvalue) {
+                    eeprom_printf("Incomplete write at log_addr: 0x%04x;\n", (uint32_t)log_addr);
+                    /* Possibly incomplete write.  Ignore and continue */
+                    continue;
+                }
+                address &= 0x1FFF;
+                address <<= 1;
+                /* Writes to addresses less than 128 are byte log entries */
+                address += FEE_BYTE_RANGE;
+            } else {
+                /* Reserved for future use */
+                if (address & FEE_VALUE_RESERVED) {
+                    eeprom_printf("Reserved encoded value at log_addr: 0x%04x;\n", (uint32_t)log_addr);
+                    continue;
+                }
+                /* Optimization for 0 or 1 values. */
+                wvalue = (address & FEE_VALUE_ENCODED) >> 13;
+                address &= 0x1FFF;
+                address <<= 1;
+            }
+            if (address < FEE_DENSITY_BYTES) {
+                eeprom_printf("DataBuf[0x%04x] = 0x%04x;\n", address, wvalue);
+                *(uint16_t *)(&DataBuf[address]) = wvalue;
+            } else {
+                eeprom_printf("DataBuf[0x%04x] cannot be set to 0x%04x [BAD ADDRESS]\n", address, wvalue);
+            }
+        }
+    }
 
-    // Clear Flags
-    // FLASH_ClearFlag(FLASH_SR_EOP|FLASH_SR_PGERR|FLASH_SR_WRPERR);
+    empty_slot = log_addr;
+
+    if (debug_eeprom) {
+        println("EEPROM_Init Final DataBuf:");
+        print_eeprom();
+    }
 
     return FEE_DENSITY_BYTES;
 }
-/*****************************************************************************
- *  Erase the whole reserved Flash Space used for user Data
- ******************************************************************************/
-void EEPROM_Erase(void) {
-    int page_num = 0;
 
-    // delete all pages from specified start page to the last page
-    do {
+/* Clear flash contents (doesn't touch in-memory DataBuf) */
+static void eeprom_clear(void) {
+    FLASH_Unlock();
+
+    for (uint16_t page_num = 0; page_num < FEE_DENSITY_PAGES; ++page_num) {
+        eeprom_printf("FLASH_ErasePage(0x%04x)\n", (uint32_t)(FEE_PAGE_BASE_ADDRESS + (page_num * FEE_PAGE_SIZE)));
         FLASH_ErasePage(FEE_PAGE_BASE_ADDRESS + (page_num * FEE_PAGE_SIZE));
-        page_num++;
-    } while (page_num < FEE_DENSITY_PAGES);
+    }
+
+    FLASH_Lock();
+
+    empty_slot = (uint16_t *)FEE_WRITE_LOG_BASE_ADDRESS;
+    eeprom_printf("eeprom_clear empty_slot: 0x%08x\n", (uint32_t)empty_slot);
 }
-/*****************************************************************************
- *  Writes once data byte to flash on specified address. If a byte is already
- *  written, the whole page must be copied to a buffer, the byte changed and
- *  the manipulated buffer written after PageErase.
- *******************************************************************************/
-uint16_t EEPROM_WriteDataByte(uint16_t Address, uint8_t DataByte) {
-    FLASH_Status FlashStatus = FLASH_COMPLETE;
 
-    uint32_t page;
-    int      i;
+/* Erase emulated eeprom */
+void EEPROM_Erase(void) {
+    eeprom_println("EEPROM_Erase");
+    /* Erase compacted pages and write log */
+    eeprom_clear();
+    /* re-initialize to reset DataBuf */
+    EEPROM_Init();
+}
 
-    // exit if desired address is above the limit (e.G. under 2048 Bytes for 4 pages)
-    if (Address > FEE_DENSITY_BYTES) {
-        return 0;
+/* Compact write log */
+static uint8_t eeprom_compact(void) {
+    /* Erase compacted pages and write log */
+    eeprom_clear();
+
+    FLASH_Unlock();
+
+    FLASH_Status final_status = FLASH_COMPLETE;
+
+    /* Write emulated eeprom contents from memory to compacted flash */
+    uint16_t *src  = (uint16_t *)DataBuf;
+    uintptr_t dest = FEE_PAGE_BASE_ADDRESS;
+    uint16_t  value;
+    for (; dest < FEE_PAGE_LAST_ADDRESS; ++src, dest += 2) {
+        value = *src;
+        if (value) {
+            eeprom_printf("FLASH_ProgramHalfWord(0x%04x, 0x%04x)\n", (uint32_t)dest, ~value);
+            FLASH_Status status = FLASH_ProgramHalfWord(dest, ~value);
+            if (status != FLASH_COMPLETE) final_status = status;
+        }
     }
 
-    // calculate which page is affected (Pagenum1/Pagenum2...PagenumN)
-    page = FEE_ADDR_OFFSET(Address) / FEE_PAGE_SIZE;
+    FLASH_Lock();
 
-    // if current data is 0xFF, the byte is empty, just overwrite with the new one
-    if ((*(__IO uint16_t *)(FEE_PAGE_BASE_ADDRESS + FEE_ADDR_OFFSET(Address))) == FEE_EMPTY_WORD) {
-        FlashStatus = FLASH_ProgramHalfWord(FEE_PAGE_BASE_ADDRESS + FEE_ADDR_OFFSET(Address), (uint16_t)(0x00FF & DataByte));
+    if (debug_eeprom) {
+        println("eeprom_compacted:");
+        print_eeprom();
+    }
+
+    return final_status;
+}
+
+static uint8_t eeprom_write_direct_entry(uint16_t Address) {
+    /* Check if we can just write this directly to the compacted flash area */
+    uintptr_t directAddress = FEE_PAGE_BASE_ADDRESS + (Address & 0xFFFE);
+    if (*(uint16_t *)directAddress == FEE_EMPTY_WORD) {
+        /* Write the value directly to the compacted area without a log entry */
+        uint16_t value = ~*(uint16_t *)(&DataBuf[Address & 0xFFFE]);
+        /* Early exit if a write isn't needed */
+        if (value == FEE_EMPTY_WORD) return FLASH_COMPLETE;
+
+        FLASH_Unlock();
+
+        eeprom_printf("FLASH_ProgramHalfWord(0x%08x, 0x%04x) [DIRECT]\n", (uint32_t)directAddress, value);
+        FLASH_Status status = FLASH_ProgramHalfWord(directAddress, value);
+
+        FLASH_Lock();
+        return status;
+    }
+    return 0;
+}
+
+static uint8_t eeprom_write_log_word_entry(uint16_t Address) {
+    FLASH_Status final_status = FLASH_COMPLETE;
+
+    uint16_t value = *(uint16_t *)(&DataBuf[Address]);
+    eeprom_printf("eeprom_write_log_word_entry(0x%04x): 0x%04x\n", Address, value);
+
+    /* MSB signifies the lowest 128-byte optimization is not in effect */
+    uint16_t encoding = FEE_WORD_ENCODING;
+    uint8_t  entry_size;
+    if (value <= 1) {
+        encoding |= value << 13;
+        entry_size = 2;
     } else {
-        // Copy Page to a buffer
-        memcpy(DataBuf, (uint8_t *)FEE_PAGE_BASE_ADDRESS + (page * FEE_PAGE_SIZE), FEE_PAGE_SIZE);  // !!! Calculate base address for the desired page
+        encoding |= FEE_VALUE_NEXT;
+        entry_size = 4;
+        /* Writes to addresses less than 128 are byte log entries */
+        Address -= FEE_BYTE_RANGE;
+    }
+
+    /* if we can't find an empty spot, we must compact emulated eeprom */
+    if (empty_slot > (uint16_t *)(FEE_WRITE_LOG_LAST_ADDRESS - entry_size)) {
+        /* compact the write log into the compacted flash area */
+        return eeprom_compact();
+    }
+
+    /* Word log writes should be word-aligned.  Take back a bit */
+    Address >>= 1;
+    Address |= encoding;
+
+    /* ok we found a place let's write our data */
+    FLASH_Unlock();
+
+    /* address */
+    eeprom_printf("FLASH_ProgramHalfWord(0x%08x, 0x%04x)\n", (uint32_t)empty_slot, Address);
+    final_status = FLASH_ProgramHalfWord((uintptr_t)empty_slot++, Address);
+
+    /* value */
+    if (encoding == (FEE_WORD_ENCODING | FEE_VALUE_NEXT)) {
+        eeprom_printf("FLASH_ProgramHalfWord(0x%08x, 0x%04x)\n", (uint32_t)empty_slot, ~value);
+        FLASH_Status status = FLASH_ProgramHalfWord((uintptr_t)empty_slot++, ~value);
+        if (status != FLASH_COMPLETE) final_status = status;
+    }
+
+    FLASH_Lock();
 
-        // check if new data is differ to current data, return if not, proceed if yes
-        if (DataByte == *(__IO uint8_t *)(FEE_PAGE_BASE_ADDRESS + FEE_ADDR_OFFSET(Address))) {
-            return 0;
+    return final_status;
+}
+
+static uint8_t eeprom_write_log_byte_entry(uint16_t Address) {
+    eeprom_printf("eeprom_write_log_byte_entry(0x%04x): 0x%02x\n", Address, DataBuf[Address]);
+
+    /* if couldn't find an empty spot, we must compact emulated eeprom */
+    if (empty_slot >= (uint16_t *)FEE_WRITE_LOG_LAST_ADDRESS) {
+        /* compact the write log into the compacted flash area */
+        return eeprom_compact();
+    }
+
+    /* ok we found a place let's write our data */
+    FLASH_Unlock();
+
+    /* Pack address and value into the same word */
+    uint16_t value = (Address << 8) | DataBuf[Address];
+
+    /* write to flash */
+    eeprom_printf("FLASH_ProgramHalfWord(0x%08x, 0x%04x)\n", (uint32_t)empty_slot, value);
+    FLASH_Status status = FLASH_ProgramHalfWord((uintptr_t)empty_slot++, value);
+
+    FLASH_Lock();
+
+    return status;
+}
+
+uint8_t EEPROM_WriteDataByte(uint16_t Address, uint8_t DataByte) {
+    /* if the address is out-of-bounds, do nothing */
+    if (Address >= FEE_DENSITY_BYTES) {
+        eeprom_printf("EEPROM_WriteDataByte(0x%04x, 0x%02x) [BAD ADDRESS]\n", Address, DataByte);
+        return FLASH_BAD_ADDRESS;
+    }
+
+    /* if the value is the same, don't bother writing it */
+    if (DataBuf[Address] == DataByte) {
+        eeprom_printf("EEPROM_WriteDataByte(0x%04x, 0x%02x) [SKIP SAME]\n", Address, DataByte);
+        return 0;
+    }
+
+    /* keep DataBuf cache in sync */
+    DataBuf[Address] = DataByte;
+    eeprom_printf("EEPROM_WriteDataByte DataBuf[0x%04x] = 0x%02x\n", Address, DataBuf[Address]);
+
+    /* perform the write into flash memory */
+    /* First, attempt to write directly into the compacted flash area */
+    FLASH_Status status = eeprom_write_direct_entry(Address);
+    if (!status) {
+        /* Otherwise append to the write log */
+        if (Address < FEE_BYTE_RANGE) {
+            status = eeprom_write_log_byte_entry(Address);
+        } else {
+            status = eeprom_write_log_word_entry(Address & 0xFFFE);
         }
+    }
+    if (status != 0 && status != FLASH_COMPLETE) {
+        eeprom_printf("EEPROM_WriteDataByte [STATUS == %d]\n", status);
+    }
+    return status;
+}
 
-        // manipulate desired data byte in temp data array if new byte is differ to the current
-        DataBuf[FEE_ADDR_OFFSET(Address) % FEE_PAGE_SIZE] = DataByte;
+uint8_t EEPROM_WriteDataWord(uint16_t Address, uint16_t DataWord) {
+    /* if the address is out-of-bounds, do nothing */
+    if (Address >= FEE_DENSITY_BYTES) {
+        eeprom_printf("EEPROM_WriteDataWord(0x%04x, 0x%04x) [BAD ADDRESS]\n", Address, DataWord);
+        return FLASH_BAD_ADDRESS;
+    }
 
-        // Erase Page
-        FlashStatus = FLASH_ErasePage(FEE_PAGE_BASE_ADDRESS + (page * FEE_PAGE_SIZE));
+    /* Check for word alignment */
+    FLASH_Status final_status = FLASH_COMPLETE;
+    if (Address % 2) {
+        final_status        = EEPROM_WriteDataByte(Address, DataWord);
+        FLASH_Status status = EEPROM_WriteDataByte(Address + 1, DataWord >> 8);
+        if (status != FLASH_COMPLETE) final_status = status;
+        if (final_status != 0 && final_status != FLASH_COMPLETE) {
+            eeprom_printf("EEPROM_WriteDataWord [STATUS == %d]\n", final_status);
+        }
+        return final_status;
+    }
+
+    /* if the value is the same, don't bother writing it */
+    uint16_t oldValue = *(uint16_t *)(&DataBuf[Address]);
+    if (oldValue == DataWord) {
+        eeprom_printf("EEPROM_WriteDataWord(0x%04x, 0x%04x) [SKIP SAME]\n", Address, DataWord);
+        return 0;
+    }
+
+    /* keep DataBuf cache in sync */
+    *(uint16_t *)(&DataBuf[Address]) = DataWord;
+    eeprom_printf("EEPROM_WriteDataWord DataBuf[0x%04x] = 0x%04x\n", Address, *(uint16_t *)(&DataBuf[Address]));
 
-        // Write new data (whole page) to flash if data has been changed
-        for (i = 0; i < (FEE_PAGE_SIZE / 2); i++) {
-            if ((__IO uint16_t)(0xFF00 | DataBuf[FEE_ADDR_OFFSET(i)]) != 0xFFFF) {
-                FlashStatus = FLASH_ProgramHalfWord((FEE_PAGE_BASE_ADDRESS + (page * FEE_PAGE_SIZE)) + (i * 2), (uint16_t)(0xFF00 | DataBuf[FEE_ADDR_OFFSET(i)]));
+    /* perform the write into flash memory */
+    /* First, attempt to write directly into the compacted flash area */
+    final_status = eeprom_write_direct_entry(Address);
+    if (!final_status) {
+        /* Otherwise append to the write log */
+        /* Check if we need to fall back to byte write */
+        if (Address < FEE_BYTE_RANGE) {
+            final_status = FLASH_COMPLETE;
+            /* Only write a byte if it has changed */
+            if ((uint8_t)oldValue != (uint8_t)DataWord) {
+                final_status = eeprom_write_log_byte_entry(Address);
             }
+            FLASH_Status status = FLASH_COMPLETE;
+            /* Only write a byte if it has changed */
+            if ((oldValue >> 8) != (DataWord >> 8)) {
+                status = eeprom_write_log_byte_entry(Address + 1);
+            }
+            if (status != FLASH_COMPLETE) final_status = status;
+        } else {
+            final_status = eeprom_write_log_word_entry(Address);
         }
     }
-    return FlashStatus;
+    if (final_status != 0 && final_status != FLASH_COMPLETE) {
+        eeprom_printf("EEPROM_WriteDataWord [STATUS == %d]\n", final_status);
+    }
+    return final_status;
 }
-/*****************************************************************************
- *  Read once data byte from a specified address.
- *******************************************************************************/
+
 uint8_t EEPROM_ReadDataByte(uint16_t Address) {
     uint8_t DataByte = 0xFF;
 
-    // Get Byte from specified address
-    DataByte = (*(__IO uint8_t *)(FEE_PAGE_BASE_ADDRESS + FEE_ADDR_OFFSET(Address)));
+    if (Address < FEE_DENSITY_BYTES) {
+        DataByte = DataBuf[Address];
+    }
+
+    eeprom_printf("EEPROM_ReadDataByte(0x%04x): 0x%02x\n", Address, DataByte);
 
     return DataByte;
 }
 
+uint16_t EEPROM_ReadDataWord(uint16_t Address) {
+    uint16_t DataWord = 0xFFFF;
+
+    if (Address < FEE_DENSITY_BYTES - 1) {
+        /* Check word alignment */
+        if (Address % 2) {
+            DataWord = DataBuf[Address] | (DataBuf[Address + 1] << 8);
+        } else {
+            DataWord = *(uint16_t *)(&DataBuf[Address]);
+        }
+    }
+
+    eeprom_printf("EEPROM_ReadDataWord(0x%04x): 0x%04x\n", Address, DataWord);
+
+    return DataWord;
+}
+
 /*****************************************************************************
  *  Wrap library in AVR style functions.
  *******************************************************************************/
-uint8_t eeprom_read_byte(const uint8_t *Address) {
-    const uint16_t p = (const uint32_t)Address;
-    return EEPROM_ReadDataByte(p);
-}
+uint8_t eeprom_read_byte(const uint8_t *Address) { return EEPROM_ReadDataByte((const uintptr_t)Address); }
 
-void eeprom_write_byte(uint8_t *Address, uint8_t Value) {
-    uint16_t p = (uint32_t)Address;
-    EEPROM_WriteDataByte(p, Value);
-}
+void eeprom_write_byte(uint8_t *Address, uint8_t Value) { EEPROM_WriteDataByte((uintptr_t)Address, Value); }
 
-void eeprom_update_byte(uint8_t *Address, uint8_t Value) {
-    uint16_t p = (uint32_t)Address;
-    EEPROM_WriteDataByte(p, Value);
-}
+void eeprom_update_byte(uint8_t *Address, uint8_t Value) { EEPROM_WriteDataByte((uintptr_t)Address, Value); }
 
-uint16_t eeprom_read_word(const uint16_t *Address) {
-    const uint16_t p = (const uint32_t)Address;
-    return EEPROM_ReadDataByte(p) | (EEPROM_ReadDataByte(p + 1) << 8);
-}
+uint16_t eeprom_read_word(const uint16_t *Address) { return EEPROM_ReadDataWord((const uintptr_t)Address); }
 
-void eeprom_write_word(uint16_t *Address, uint16_t Value) {
-    uint16_t p = (uint32_t)Address;
-    EEPROM_WriteDataByte(p, (uint8_t)Value);
-    EEPROM_WriteDataByte(p + 1, (uint8_t)(Value >> 8));
-}
+void eeprom_write_word(uint16_t *Address, uint16_t Value) { EEPROM_WriteDataWord((uintptr_t)Address, Value); }
 
-void eeprom_update_word(uint16_t *Address, uint16_t Value) {
-    uint16_t p = (uint32_t)Address;
-    EEPROM_WriteDataByte(p, (uint8_t)Value);
-    EEPROM_WriteDataByte(p + 1, (uint8_t)(Value >> 8));
-}
+void eeprom_update_word(uint16_t *Address, uint16_t Value) { EEPROM_WriteDataWord((uintptr_t)Address, Value); }
 
 uint32_t eeprom_read_dword(const uint32_t *Address) {
-    const uint16_t p = (const uint32_t)Address;
-    return EEPROM_ReadDataByte(p) | (EEPROM_ReadDataByte(p + 1) << 8) | (EEPROM_ReadDataByte(p + 2) << 16) | (EEPROM_ReadDataByte(p + 3) << 24);
+    const uint16_t p = (const uintptr_t)Address;
+    /* Check word alignment */
+    if (p % 2) {
+        /* Not aligned */
+        return (uint32_t)EEPROM_ReadDataByte(p) | (uint32_t)(EEPROM_ReadDataWord(p + 1) << 8) | (uint32_t)(EEPROM_ReadDataByte(p + 3) << 24);
+    } else {
+        /* Aligned */
+        return EEPROM_ReadDataWord(p) | (EEPROM_ReadDataWord(p + 2) << 16);
+    }
 }
 
 void eeprom_write_dword(uint32_t *Address, uint32_t Value) {
-    uint16_t p = (const uint32_t)Address;
-    EEPROM_WriteDataByte(p, (uint8_t)Value);
-    EEPROM_WriteDataByte(p + 1, (uint8_t)(Value >> 8));
-    EEPROM_WriteDataByte(p + 2, (uint8_t)(Value >> 16));
-    EEPROM_WriteDataByte(p + 3, (uint8_t)(Value >> 24));
-}
-
-void eeprom_update_dword(uint32_t *Address, uint32_t Value) {
-    uint16_t p             = (const uint32_t)Address;
-    uint32_t existingValue = EEPROM_ReadDataByte(p) | (EEPROM_ReadDataByte(p + 1) << 8) | (EEPROM_ReadDataByte(p + 2) << 16) | (EEPROM_ReadDataByte(p + 3) << 24);
-    if (Value != existingValue) {
+    uint16_t p = (const uintptr_t)Address;
+    /* Check word alignment */
+    if (p % 2) {
+        /* Not aligned */
         EEPROM_WriteDataByte(p, (uint8_t)Value);
-        EEPROM_WriteDataByte(p + 1, (uint8_t)(Value >> 8));
-        EEPROM_WriteDataByte(p + 2, (uint8_t)(Value >> 16));
+        EEPROM_WriteDataWord(p + 1, (uint16_t)(Value >> 8));
         EEPROM_WriteDataByte(p + 3, (uint8_t)(Value >> 24));
+    } else {
+        /* Aligned */
+        EEPROM_WriteDataWord(p, (uint16_t)Value);
+        EEPROM_WriteDataWord(p + 2, (uint16_t)(Value >> 16));
     }
 }
 
+void eeprom_update_dword(uint32_t *Address, uint32_t Value) { eeprom_write_dword(Address, Value); }
+
 void eeprom_read_block(void *buf, const void *addr, size_t len) {
-    const uint8_t *p    = (const uint8_t *)addr;
+    const uint8_t *src  = (const uint8_t *)addr;
     uint8_t *      dest = (uint8_t *)buf;
-    while (len--) {
-        *dest++ = eeprom_read_byte(p++);
+
+    /* Check word alignment */
+    if (len && (uintptr_t)src % 2) {
+        /* Read the unaligned first byte */
+        *dest++ = eeprom_read_byte(src++);
+        --len;
+    }
+
+    uint16_t value;
+    bool     aligned = ((uintptr_t)dest % 2 == 0);
+    while (len > 1) {
+        value = eeprom_read_word((uint16_t *)src);
+        if (aligned) {
+            *(uint16_t *)dest = value;
+            dest += 2;
+        } else {
+            *dest++ = value;
+            *dest++ = value >> 8;
+        }
+        src += 2;
+        len -= 2;
+    }
+    if (len) {
+        *dest = eeprom_read_byte(src);
     }
 }
 
 void eeprom_write_block(const void *buf, void *addr, size_t len) {
-    uint8_t *      p   = (uint8_t *)addr;
-    const uint8_t *src = (const uint8_t *)buf;
-    while (len--) {
-        eeprom_write_byte(p++, *src++);
+    uint8_t *      dest = (uint8_t *)addr;
+    const uint8_t *src  = (const uint8_t *)buf;
+
+    /* Check word alignment */
+    if (len && (uintptr_t)dest % 2) {
+        /* Write the unaligned first byte */
+        eeprom_write_byte(dest++, *src++);
+        --len;
     }
-}
 
-void eeprom_update_block(const void *buf, void *addr, size_t len) {
-    uint8_t *      p   = (uint8_t *)addr;
-    const uint8_t *src = (const uint8_t *)buf;
-    while (len--) {
-        eeprom_write_byte(p++, *src++);
+    uint16_t value;
+    bool     aligned = ((uintptr_t)src % 2 == 0);
+    while (len > 1) {
+        if (aligned) {
+            value = *(uint16_t *)src;
+        } else {
+            value = *(uint8_t *)src | (*(uint8_t *)(src + 1) << 8);
+        }
+        eeprom_write_word((uint16_t *)dest, value);
+        dest += 2;
+        src += 2;
+        len -= 2;
+    }
+
+    if (len) {
+        eeprom_write_byte(dest, *src);
     }
 }
+
+void eeprom_update_block(const void *buf, void *addr, size_t len) { eeprom_write_block(buf, addr, len); }
diff --git a/tmk_core/common/chibios/eeprom_stm32.h b/tmk_core/common/chibios/eeprom_stm32.h
index 4dac7c1b59..8fcfb556b8 100644
--- a/tmk_core/common/chibios/eeprom_stm32.h
+++ b/tmk_core/common/chibios/eeprom_stm32.h
@@ -23,62 +23,11 @@
 
 #pragma once
 
-#include <ch.h>
-#include <hal.h>
-#include "flash_stm32.h"
-
-// HACK ALERT. This definition may not match your processor
-// To Do. Work out correct value for EEPROM_PAGE_SIZE on the STM32F103CT6 etc
-#if defined(EEPROM_EMU_STM32F303xC)
-#    define MCU_STM32F303CC
-#elif defined(EEPROM_EMU_STM32F103xB)
-#    define MCU_STM32F103RB
-#elif defined(EEPROM_EMU_STM32F072xB)
-#    define MCU_STM32F072CB
-#elif defined(EEPROM_EMU_STM32F042x6)
-#    define MCU_STM32F042K6
-#else
-#    error "not implemented."
-#endif
-
-#ifndef EEPROM_PAGE_SIZE
-#    if defined(MCU_STM32F103RB) || defined(MCU_STM32F042K6)
-#        define FEE_PAGE_SIZE (uint16_t)0x400  // Page size = 1KByte
-#        define FEE_DENSITY_PAGES 2            // How many pages are used
-#    elif defined(MCU_STM32F103ZE) || defined(MCU_STM32F103RE) || defined(MCU_STM32F103RD) || defined(MCU_STM32F303CC) || defined(MCU_STM32F072CB)
-#        define FEE_PAGE_SIZE (uint16_t)0x800  // Page size = 2KByte
-#        define FEE_DENSITY_PAGES 4            // How many pages are used
-#    else
-#        error "No MCU type specified. Add something like -DMCU_STM32F103RB to your compiler arguments (probably in a Makefile)."
-#    endif
-#endif
-
-#ifndef EEPROM_START_ADDRESS
-#    if defined(MCU_STM32F103RB) || defined(MCU_STM32F072CB)
-#        define FEE_MCU_FLASH_SIZE 128  // Size in Kb
-#    elif defined(MCU_STM32F042K6)
-#        define FEE_MCU_FLASH_SIZE 32  // Size in Kb
-#    elif defined(MCU_STM32F103ZE) || defined(MCU_STM32F103RE)
-#        define FEE_MCU_FLASH_SIZE 512  // Size in Kb
-#    elif defined(MCU_STM32F103RD)
-#        define FEE_MCU_FLASH_SIZE 384  // Size in Kb
-#    elif defined(MCU_STM32F303CC)
-#        define FEE_MCU_FLASH_SIZE 256  // Size in Kb
-#    else
-#        error "No MCU type specified. Add something like -DMCU_STM32F103RB to your compiler arguments (probably in a Makefile)."
-#    endif
-#endif
-
-// DONT CHANGE
-// Choose location for the first EEPROM Page address on the top of flash
-#define FEE_PAGE_BASE_ADDRESS ((uint32_t)(0x8000000 + FEE_MCU_FLASH_SIZE * 1024 - FEE_DENSITY_PAGES * FEE_PAGE_SIZE))
-#define FEE_DENSITY_BYTES ((FEE_PAGE_SIZE / 2) * FEE_DENSITY_PAGES - 1)
-#define FEE_LAST_PAGE_ADDRESS (FEE_PAGE_BASE_ADDRESS + (FEE_PAGE_SIZE * FEE_DENSITY_PAGES))
-#define FEE_EMPTY_WORD ((uint16_t)0xFFFF)
-#define FEE_ADDR_OFFSET(Address) (Address * 2)  // 1Byte per Word will be saved to preserve Flash
-
-// Use this function to initialize the functionality
 uint16_t EEPROM_Init(void);
 void     EEPROM_Erase(void);
-uint16_t EEPROM_WriteDataByte(uint16_t Address, uint8_t DataByte);
+uint8_t  EEPROM_WriteDataByte(uint16_t Address, uint8_t DataByte);
+uint8_t  EEPROM_WriteDataWord(uint16_t Address, uint16_t DataWord);
 uint8_t  EEPROM_ReadDataByte(uint16_t Address);
+uint16_t EEPROM_ReadDataWord(uint16_t Address);
+
+void print_eeprom(void);
diff --git a/tmk_core/common/chibios/flash_stm32.h b/tmk_core/common/chibios/flash_stm32.h
index 90d5bff47e..9c6a7cc50f 100644
--- a/tmk_core/common/chibios/flash_stm32.h
+++ b/tmk_core/common/chibios/flash_stm32.h
@@ -22,8 +22,11 @@
 extern "C" {
 #endif
 
-#include <ch.h>
-#include <hal.h>
+#include <stdint.h>
+
+#ifdef FLASH_STM32_MOCKED
+extern uint8_t FlashBuf[MOCK_FLASH_SIZE];
+#endif
 
 typedef enum { FLASH_BUSY = 1, FLASH_ERROR_PG, FLASH_ERROR_WRP, FLASH_ERROR_OPT, FLASH_COMPLETE, FLASH_TIMEOUT, FLASH_BAD_ADDRESS } FLASH_Status;
 
diff --git a/tmk_core/common/test/eeprom_stm32_tests.cpp b/tmk_core/common/test/eeprom_stm32_tests.cpp
new file mode 100644
index 0000000000..aa84492b87
--- /dev/null
+++ b/tmk_core/common/test/eeprom_stm32_tests.cpp
@@ -0,0 +1,438 @@
+/* Copyright 2021 by Don Kjer
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "gtest/gtest.h"
+
+extern "C" {
+#include "flash_stm32.h"
+#include "eeprom_stm32.h"
+#include "eeprom.h"
+}
+
+/* Mock Flash Parameters:
+ *
+ * === Large Layout ===
+ * flash size: 65536
+ * page size: 2048
+ * density pages: 16
+ * Simulated EEPROM size: 16384
+ *
+ * FlashBuf Layout:
+ * [Unused | Compact |  Write Log  ]
+ * [0......|32768......|49152......65535]
+ *
+ * === Tiny Layout ===
+ * flash size: 1024
+ * page size: 512
+ * density pages: 1
+ * Simulated EEPROM size: 256
+ *
+ * FlashBuf Layout:
+ * [Unused | Compact |  Write Log  ]
+ * [0......|512......|768......1023]
+ *
+ */
+
+#define EEPROM_SIZE (FEE_PAGE_SIZE * FEE_DENSITY_PAGES / 2)
+#define LOG_SIZE EEPROM_SIZE
+#define LOG_BASE (MOCK_FLASH_SIZE - LOG_SIZE)
+#define EEPROM_BASE (LOG_BASE - EEPROM_SIZE)
+
+/* Log encoding helpers */
+#define BYTE_VALUE(addr, value) (((addr) << 8) | (value))
+#define WORD_ZERO(addr) (0x8000 | ((addr) >> 1))
+#define WORD_ONE(addr) (0xA000 | ((addr) >> 1))
+#define WORD_NEXT(addr) (0xE000 | (((addr)-0x80) >> 1))
+
+class EepromStm32Test : public testing::Test {
+   public:
+    EepromStm32Test() {}
+    ~EepromStm32Test() {}
+
+   protected:
+    void SetUp() override { EEPROM_Erase(); }
+
+    void TearDown() override {
+#ifdef EEPROM_DEBUG
+        dumpEepromDataBuf();
+#endif
+    }
+};
+
+TEST_F(EepromStm32Test, TestErase) {
+    EEPROM_WriteDataByte(0, 0x42);
+    EEPROM_Erase();
+    EXPECT_EQ(EEPROM_ReadDataByte(0), 0);
+    EXPECT_EQ(EEPROM_ReadDataByte(1), 0);
+}
+
+TEST_F(EepromStm32Test, TestReadGarbage) {
+    uint8_t garbage = 0x3c;
+    for (int i = 0; i < MOCK_FLASH_SIZE; ++i) {
+        garbage ^= 0xa3;
+        garbage += i;
+        FlashBuf[i] = garbage;
+    }
+    EEPROM_Init();  // Just verify we don't crash
+}
+
+TEST_F(EepromStm32Test, TestWriteBadAddress) {
+    EXPECT_EQ(EEPROM_WriteDataByte(EEPROM_SIZE, 0x42), FLASH_BAD_ADDRESS);
+    EXPECT_EQ(EEPROM_WriteDataWord(EEPROM_SIZE - 1, 0xbeef), FLASH_BAD_ADDRESS);
+    EXPECT_EQ(EEPROM_WriteDataWord(EEPROM_SIZE, 0xbeef), FLASH_BAD_ADDRESS);
+}
+
+TEST_F(EepromStm32Test, TestReadBadAddress) {
+    EXPECT_EQ(EEPROM_ReadDataByte(EEPROM_SIZE), 0xFF);
+    EXPECT_EQ(EEPROM_ReadDataWord(EEPROM_SIZE - 1), 0xFFFF);
+    EXPECT_EQ(EEPROM_ReadDataWord(EEPROM_SIZE), 0xFFFF);
+    EXPECT_EQ(eeprom_read_dword((uint32_t*)(EEPROM_SIZE - 4)), 0);
+    EXPECT_EQ(eeprom_read_dword((uint32_t*)(EEPROM_SIZE - 3)), 0xFF000000);
+    EXPECT_EQ(eeprom_read_dword((uint32_t*)EEPROM_SIZE), 0xFFFFFFFF);
+}
+
+TEST_F(EepromStm32Test, TestReadByte) {
+    /* Direct compacted-area baseline: Address < 0x80 */
+    FlashBuf[EEPROM_BASE + 2] = ~0xef;
+    FlashBuf[EEPROM_BASE + 3] = ~0xbe;
+    /* Direct compacted-area baseline: Address >= 0x80 */
+    FlashBuf[EEPROM_BASE + EEPROM_SIZE - 2] = ~0x78;
+    FlashBuf[EEPROM_BASE + EEPROM_SIZE - 1] = ~0x56;
+    /* Check values */
+    EEPROM_Init();
+    EXPECT_EQ(EEPROM_ReadDataByte(2), 0xef);
+    EXPECT_EQ(EEPROM_ReadDataByte(3), 0xbe);
+    EXPECT_EQ(EEPROM_ReadDataByte(EEPROM_SIZE - 2), 0x78);
+    EXPECT_EQ(EEPROM_ReadDataByte(EEPROM_SIZE - 1), 0x56);
+    /* Write Log byte value */
+    FlashBuf[LOG_BASE]     = 0x65;
+    FlashBuf[LOG_BASE + 1] = 3;
+    /* Write Log word value */
+    *(uint16_t*)&FlashBuf[LOG_BASE + 2] = WORD_NEXT(EEPROM_SIZE - 2);
+    *(uint16_t*)&FlashBuf[LOG_BASE + 4] = ~0x9abc;
+    /* Check values */
+    EEPROM_Init();
+    EXPECT_EQ(EEPROM_ReadDataByte(2), 0xef);
+    EXPECT_EQ(EEPROM_ReadDataByte(3), 0x65);
+    EXPECT_EQ(EEPROM_ReadDataByte(EEPROM_SIZE - 2), 0xbc);
+    EXPECT_EQ(EEPROM_ReadDataByte(EEPROM_SIZE - 1), 0x9a);
+}
+
+TEST_F(EepromStm32Test, TestWriteByte) {
+    /* Direct compacted-area baseline: Address < 0x80 */
+    EEPROM_WriteDataByte(2, 0xef);
+    EEPROM_WriteDataByte(3, 0xbe);
+    /* Direct compacted-area baseline: Address >= 0x80 */
+    EEPROM_WriteDataByte(EEPROM_SIZE - 2, 0x78);
+    EEPROM_WriteDataByte(EEPROM_SIZE - 1, 0x56);
+    /* Check values */
+    /* First write in each aligned word should have been direct */
+    EXPECT_EQ(FlashBuf[EEPROM_BASE + 2], (uint8_t)~0xef);
+    EXPECT_EQ(FlashBuf[EEPROM_BASE + EEPROM_SIZE - 2], (uint8_t)~0x78);
+
+    /* Second write per aligned word requires a log entry */
+    EXPECT_EQ(*(uint16_t*)&FlashBuf[LOG_BASE], BYTE_VALUE(3, 0xbe));
+    EXPECT_EQ(*(uint16_t*)&FlashBuf[LOG_BASE + 2], WORD_NEXT(EEPROM_SIZE - 1));
+    EXPECT_EQ(*(uint16_t*)&FlashBuf[LOG_BASE + 4], (uint16_t)~0x5678);
+}
+
+TEST_F(EepromStm32Test, TestByteRoundTrip) {
+    /* Direct compacted-area: Address < 0x80 */
+    EEPROM_WriteDataWord(0, 0xdead);
+    EEPROM_WriteDataByte(2, 0xef);
+    EEPROM_WriteDataByte(3, 0xbe);
+    /* Direct compacted-area: Address >= 0x80 */
+    EEPROM_WriteDataByte(EEPROM_SIZE - 2, 0x78);
+    EEPROM_WriteDataByte(EEPROM_SIZE - 1, 0x56);
+    /* Check values */
+    EEPROM_Init();
+    EXPECT_EQ(EEPROM_ReadDataByte(0), 0xad);
+    EXPECT_EQ(EEPROM_ReadDataByte(1), 0xde);
+    EXPECT_EQ(EEPROM_ReadDataByte(2), 0xef);
+    EXPECT_EQ(EEPROM_ReadDataByte(3), 0xbe);
+    EXPECT_EQ(EEPROM_ReadDataByte(EEPROM_SIZE - 2), 0x78);
+    EXPECT_EQ(EEPROM_ReadDataByte(EEPROM_SIZE - 1), 0x56);
+    /* Write log entries */
+    EEPROM_WriteDataByte(2, 0x80);
+    EEPROM_WriteDataByte(EEPROM_SIZE - 2, 0x3c);
+    /* Check values */
+    EEPROM_Init();
+    EXPECT_EQ(EEPROM_ReadDataByte(2), 0x80);
+    EXPECT_EQ(EEPROM_ReadDataByte(3), 0xbe);
+    EXPECT_EQ(EEPROM_ReadDataByte(EEPROM_SIZE - 2), 0x3c);
+    EXPECT_EQ(EEPROM_ReadDataByte(EEPROM_SIZE - 1), 0x56);
+}
+
+TEST_F(EepromStm32Test, TestReadWord) {
+    /* Direct compacted-area baseline: Address < 0x80 */
+    FlashBuf[EEPROM_BASE + 0] = ~0xad;
+    FlashBuf[EEPROM_BASE + 1] = ~0xde;
+    /* Direct compacted-area baseline: Address >= 0x80 */
+    FlashBuf[EEPROM_BASE + 200]             = ~0xcd;
+    FlashBuf[EEPROM_BASE + 201]             = ~0xab;
+    FlashBuf[EEPROM_BASE + EEPROM_SIZE - 4] = ~0x34;
+    FlashBuf[EEPROM_BASE + EEPROM_SIZE - 3] = ~0x12;
+    FlashBuf[EEPROM_BASE + EEPROM_SIZE - 2] = ~0x78;
+    FlashBuf[EEPROM_BASE + EEPROM_SIZE - 1] = ~0x56;
+    /* Check values */
+    EEPROM_Init();
+    EXPECT_EQ(EEPROM_ReadDataWord(0), 0xdead);
+    EXPECT_EQ(EEPROM_ReadDataWord(200), 0xabcd);
+    EXPECT_EQ(EEPROM_ReadDataWord(EEPROM_SIZE - 4), 0x1234);
+    EXPECT_EQ(EEPROM_ReadDataWord(EEPROM_SIZE - 2), 0x5678);
+    /* Write Log word zero-encoded */
+    *(uint16_t*)&FlashBuf[LOG_BASE] = WORD_ZERO(200);
+    /* Write Log word one-encoded */
+    *(uint16_t*)&FlashBuf[LOG_BASE + 2] = WORD_ONE(EEPROM_SIZE - 4);
+    /* Write Log word value */
+    *(uint16_t*)&FlashBuf[LOG_BASE + 4] = WORD_NEXT(EEPROM_SIZE - 2);
+    *(uint16_t*)&FlashBuf[LOG_BASE + 6] = ~0x9abc;
+    /* Check values */
+    EEPROM_Init();
+    EXPECT_EQ(EEPROM_ReadDataWord(200), 0);
+    EXPECT_EQ(EEPROM_ReadDataWord(EEPROM_SIZE - 4), 1);
+    EXPECT_EQ(EEPROM_ReadDataWord(EEPROM_SIZE - 2), 0x9abc);
+}
+
+TEST_F(EepromStm32Test, TestWriteWord) {
+    /* Direct compacted-area: Address < 0x80 */
+    EEPROM_WriteDataWord(0, 0xdead);  // Aligned
+    EEPROM_WriteDataWord(3, 0xbeef);  // Unaligned
+    /* Direct compacted-area: Address >= 0x80 */
+    EEPROM_WriteDataWord(200, 0xabcd);  // Aligned
+    EEPROM_WriteDataWord(203, 0x9876);  // Unaligned
+    EEPROM_WriteDataWord(EEPROM_SIZE - 4, 0x1234);
+    EEPROM_WriteDataWord(EEPROM_SIZE - 2, 0x5678);
+    /* Write Log word zero-encoded */
+    EEPROM_WriteDataWord(EEPROM_SIZE - 4, 0);
+    /* Write Log word one-encoded */
+    EEPROM_WriteDataWord(EEPROM_SIZE - 2, 1);
+    /* Write Log word value aligned */
+    EEPROM_WriteDataWord(200, 0x4321);  // Aligned
+    /* Write Log word value unaligned */
+    EEPROM_WriteDataByte(202, 0x3c);    // Set neighboring byte
+    EEPROM_WriteDataWord(203, 0xcdef);  // Unaligned
+    /* Check values */
+    /* Direct compacted-area */
+    EXPECT_EQ(*(uint16_t*)&FlashBuf[EEPROM_BASE], (uint16_t)~0xdead);
+    EXPECT_EQ(*(uint16_t*)&FlashBuf[EEPROM_BASE + 3], (uint16_t)~0xbeef);
+    EXPECT_EQ(*(uint16_t*)&FlashBuf[EEPROM_BASE + 200], (uint16_t)~0xabcd);
+    EXPECT_EQ(FlashBuf[EEPROM_BASE + 203], (uint8_t)~0x76);
+    EXPECT_EQ(FlashBuf[EEPROM_BASE + 204], (uint8_t)~0x98);
+    EXPECT_EQ(*(uint16_t*)&FlashBuf[EEPROM_BASE + EEPROM_SIZE - 4], (uint16_t)~0x1234);
+    EXPECT_EQ(*(uint16_t*)&FlashBuf[EEPROM_BASE + EEPROM_SIZE - 2], (uint16_t)~0x5678);
+    /* Write Log word zero-encoded */
+    EXPECT_EQ(*(uint16_t*)&FlashBuf[LOG_BASE], WORD_ZERO(EEPROM_SIZE - 4));
+    /* Write Log word one-encoded */
+    EXPECT_EQ(*(uint16_t*)&FlashBuf[LOG_BASE + 2], WORD_ONE(EEPROM_SIZE - 2));
+    /* Write Log word value aligned */
+    EXPECT_EQ(*(uint16_t*)&FlashBuf[LOG_BASE + 4], WORD_NEXT(200));
+    EXPECT_EQ(*(uint16_t*)&FlashBuf[LOG_BASE + 6], (uint16_t)~0x4321);
+    /* Write Log word value unaligned */
+    EXPECT_EQ(*(uint16_t*)&FlashBuf[LOG_BASE + 8], WORD_NEXT(202));
+    EXPECT_EQ(*(uint16_t*)&FlashBuf[LOG_BASE + 10], (uint16_t)~0x763c);
+    EXPECT_EQ(*(uint16_t*)&FlashBuf[LOG_BASE + 12], WORD_NEXT(202));
+    EXPECT_EQ(*(uint16_t*)&FlashBuf[LOG_BASE + 14], (uint16_t)~0xef3c);
+    EXPECT_EQ(*(uint16_t*)&FlashBuf[LOG_BASE + 16], WORD_NEXT(204));
+    EXPECT_EQ(*(uint16_t*)&FlashBuf[LOG_BASE + 18], (uint16_t)~0x00cd);
+}
+
+TEST_F(EepromStm32Test, TestWordRoundTrip) {
+    /* Direct compacted-area: Address < 0x80 */
+    EEPROM_WriteDataWord(0, 0xdead);  // Aligned
+    EEPROM_WriteDataWord(3, 0xbeef);  // Unaligned
+    /* Direct compacted-area: Address >= 0x80 */
+    EEPROM_WriteDataWord(200, 0xabcd);  // Aligned
+    EEPROM_WriteDataWord(203, 0x9876);  // Unaligned
+    EEPROM_WriteDataWord(EEPROM_SIZE - 4, 0x1234);
+    EEPROM_WriteDataWord(EEPROM_SIZE - 2, 0x5678);
+    /* Check values */
+    EEPROM_Init();
+    EXPECT_EQ(EEPROM_ReadDataWord(0), 0xdead);
+    EXPECT_EQ(EEPROM_ReadDataWord(3), 0xbeef);
+    EXPECT_EQ(EEPROM_ReadDataWord(200), 0xabcd);
+    EXPECT_EQ(EEPROM_ReadDataWord(203), 0x9876);
+    EXPECT_EQ(EEPROM_ReadDataWord(EEPROM_SIZE - 4), 0x1234);
+    EXPECT_EQ(EEPROM_ReadDataWord(EEPROM_SIZE - 2), 0x5678);
+
+    /* Write Log word zero-encoded */
+    EEPROM_WriteDataWord(EEPROM_SIZE - 4, 0);
+    /* Write Log word one-encoded */
+    EEPROM_WriteDataWord(EEPROM_SIZE - 2, 1);
+    /* Write Log word value aligned */
+    EEPROM_WriteDataWord(200, 0x4321);  // Aligned
+    /* Write Log word value unaligned */
+    EEPROM_WriteDataByte(202, 0x3c);    // Set neighboring byte
+    EEPROM_WriteDataWord(203, 0xcdef);  // Unaligned
+    /* Check values */
+    EEPROM_Init();
+    EXPECT_EQ(EEPROM_ReadDataWord(200), 0x4321);
+    EXPECT_EQ(EEPROM_ReadDataByte(202), 0x3c);
+    EXPECT_EQ(EEPROM_ReadDataWord(203), 0xcdef);
+    EXPECT_EQ(EEPROM_ReadDataWord(EEPROM_SIZE - 4), 0);
+    EXPECT_EQ(EEPROM_ReadDataWord(EEPROM_SIZE - 2), 1);
+}
+
+TEST_F(EepromStm32Test, TestByteWordBoundary) {
+    /* Direct compacted-area write */
+    EEPROM_WriteDataWord(0x7e, 0xdead);
+    EEPROM_WriteDataWord(0x80, 0xbeef);
+    /* Byte log entry */
+    EEPROM_WriteDataByte(0x7f, 0x3c);
+    /* Word log entry */
+    EEPROM_WriteDataByte(0x80, 0x18);
+    /* Check values */
+    EEPROM_Init();
+    EXPECT_EQ(EEPROM_ReadDataWord(0x7e), 0x3cad);
+    EXPECT_EQ(EEPROM_ReadDataWord(0x80), 0xbe18);
+    EXPECT_EQ(*(uint16_t*)&FlashBuf[LOG_BASE], BYTE_VALUE(0x7f, 0x3c));
+    EXPECT_EQ(*(uint16_t*)&FlashBuf[LOG_BASE + 2], WORD_NEXT(0x80));
+    EXPECT_EQ(*(uint16_t*)&FlashBuf[LOG_BASE + 4], (uint16_t)~0xbe18);
+    /* Byte log entries */
+    EEPROM_WriteDataWord(0x7e, 0xcafe);
+    /* Check values */
+    EEPROM_Init();
+    EXPECT_EQ(EEPROM_ReadDataWord(0x7e), 0xcafe);
+    EXPECT_EQ(*(uint16_t*)&FlashBuf[LOG_BASE + 6], BYTE_VALUE(0x7e, 0xfe));
+    EXPECT_EQ(*(uint16_t*)&FlashBuf[LOG_BASE + 8], BYTE_VALUE(0x7f, 0xca));
+    /* Byte and Word log entries */
+    EEPROM_WriteDataWord(0x7f, 0xba5e);
+    /* Check values */
+    EEPROM_Init();
+    EXPECT_EQ(EEPROM_ReadDataWord(0x7f), 0xba5e);
+    EXPECT_EQ(*(uint16_t*)&FlashBuf[LOG_BASE + 10], BYTE_VALUE(0x7f, 0x5e));
+    EXPECT_EQ(*(uint16_t*)&FlashBuf[LOG_BASE + 12], WORD_NEXT(0x80));
+    EXPECT_EQ(*(uint16_t*)&FlashBuf[LOG_BASE + 14], (uint16_t)~0xbeba);
+    /* Word log entry */
+    EEPROM_WriteDataWord(0x80, 0xf00d);
+    /* Check values */
+    EEPROM_Init();
+    EXPECT_EQ(EEPROM_ReadDataWord(0x80), 0xf00d);
+    EXPECT_EQ(*(uint16_t*)&FlashBuf[LOG_BASE + 16], WORD_NEXT(0x80));
+    EXPECT_EQ(*(uint16_t*)&FlashBuf[LOG_BASE + 18], (uint16_t)~0xf00d);
+}
+
+TEST_F(EepromStm32Test, TestDWordRoundTrip) {
+    /* Direct compacted-area: Address < 0x80 */
+    eeprom_write_dword((uint32_t*)0, 0xdeadbeef);  // Aligned
+    eeprom_write_dword((uint32_t*)9, 0x12345678);  // Unaligned
+    /* Direct compacted-area: Address >= 0x80 */
+    eeprom_write_dword((uint32_t*)200, 0xfacef00d);
+    eeprom_write_dword((uint32_t*)(EEPROM_SIZE - 4), 0xba5eba11);  // Aligned
+    eeprom_write_dword((uint32_t*)(EEPROM_SIZE - 9), 0xcafed00d);  // Unaligned
+    /* Check direct values */
+    EEPROM_Init();
+    EXPECT_EQ(eeprom_read_dword((uint32_t*)0), 0xdeadbeef);
+    EXPECT_EQ(eeprom_read_dword((uint32_t*)9), 0x12345678);
+    EXPECT_EQ(eeprom_read_dword((uint32_t*)200), 0xfacef00d);
+    EXPECT_EQ(eeprom_read_dword((uint32_t*)(EEPROM_SIZE - 4)), 0xba5eba11);  // Aligned
+    EXPECT_EQ(eeprom_read_dword((uint32_t*)(EEPROM_SIZE - 9)), 0xcafed00d);  // Unaligned
+    /* Write Log byte encoded */
+    eeprom_write_dword((uint32_t*)0, 0xdecafbad);
+    eeprom_write_dword((uint32_t*)9, 0x87654321);
+    /* Write Log word encoded */
+    eeprom_write_dword((uint32_t*)200, 1);
+    /* Write Log word value aligned */
+    eeprom_write_dword((uint32_t*)(EEPROM_SIZE - 4), 0xdeadc0de);  // Aligned
+    eeprom_write_dword((uint32_t*)(EEPROM_SIZE - 9), 0x6789abcd);  // Unaligned
+    /* Check log values */
+    EEPROM_Init();
+    EXPECT_EQ(eeprom_read_dword((uint32_t*)0), 0xdecafbad);
+    EXPECT_EQ(eeprom_read_dword((uint32_t*)9), 0x87654321);
+    EXPECT_EQ(eeprom_read_dword((uint32_t*)200), 1);
+    EXPECT_EQ(eeprom_read_dword((uint32_t*)(EEPROM_SIZE - 4)), 0xdeadc0de);  // Aligned
+    EXPECT_EQ(eeprom_read_dword((uint32_t*)(EEPROM_SIZE - 9)), 0x6789abcd);  // Unaligned
+}
+
+TEST_F(EepromStm32Test, TestBlockRoundTrip) {
+    char  src0[] = "0123456789abcdef";
+    void* src1   = (void*)&src0[1];
+    /* Various alignments of src & dst, Address < 0x80 */
+    eeprom_write_block(src0, (void*)0, sizeof(src0));
+    eeprom_write_block(src0, (void*)21, sizeof(src0));
+    eeprom_write_block(src1, (void*)40, sizeof(src0) - 1);
+    eeprom_write_block(src1, (void*)61, sizeof(src0) - 1);
+    /* Various alignments of src & dst, Address >= 0x80 */
+    eeprom_write_block(src0, (void*)140, sizeof(src0));
+    eeprom_write_block(src0, (void*)161, sizeof(src0));
+    eeprom_write_block(src1, (void*)180, sizeof(src0) - 1);
+    eeprom_write_block(src1, (void*)201, sizeof(src0) - 1);
+
+    /* Check values */
+    EEPROM_Init();
+
+    char  dstBuf[256] = {0};
+    char* dst0a       = (char*)dstBuf;
+    char* dst0b       = (char*)&dstBuf[20];
+    char* dst1a       = (char*)&dstBuf[41];
+    char* dst1b       = (char*)&dstBuf[61];
+    char* dst0c       = (char*)&dstBuf[80];
+    char* dst0d       = (char*)&dstBuf[100];
+    char* dst1c       = (char*)&dstBuf[121];
+    char* dst1d       = (char*)&dstBuf[141];
+    eeprom_read_block((void*)dst0a, (void*)0, sizeof(src0));
+    eeprom_read_block((void*)dst0b, (void*)21, sizeof(src0));
+    eeprom_read_block((void*)dst1a, (void*)40, sizeof(src0) - 1);
+    eeprom_read_block((void*)dst1b, (void*)61, sizeof(src0) - 1);
+    eeprom_read_block((void*)dst0c, (void*)140, sizeof(src0));
+    eeprom_read_block((void*)dst0d, (void*)161, sizeof(src0));
+    eeprom_read_block((void*)dst1c, (void*)180, sizeof(src0) - 1);
+    eeprom_read_block((void*)dst1d, (void*)201, sizeof(src0) - 1);
+    EXPECT_EQ(strcmp((char*)src0, dst0a), 0);
+    EXPECT_EQ(strcmp((char*)src0, dst0b), 0);
+    EXPECT_EQ(strcmp((char*)src0, dst0c), 0);
+    EXPECT_EQ(strcmp((char*)src0, dst0d), 0);
+    EXPECT_EQ(strcmp((char*)src1, dst1a), 0);
+    EXPECT_EQ(strcmp((char*)src1, dst1b), 0);
+    EXPECT_EQ(strcmp((char*)src1, dst1c), 0);
+    EXPECT_EQ(strcmp((char*)src1, dst1d), 0);
+}
+
+TEST_F(EepromStm32Test, TestCompaction) {
+    /* Direct writes */
+    eeprom_write_dword((uint32_t*)0, 0xdeadbeef);
+    eeprom_write_byte((uint8_t*)4, 0x3c);
+    eeprom_write_word((uint16_t*)6, 0xd00d);
+    eeprom_write_dword((uint32_t*)150, 0xcafef00d);
+    eeprom_write_dword((uint32_t*)200, 0x12345678);
+    /* Fill write log entries */
+    uint32_t i;
+    uint32_t val = 0xd8453c6b;
+    for (i = 0; i < (LOG_SIZE / (sizeof(uint32_t) * 2)); i++) {
+        val ^= 0x593ca5b3;
+        val += i;
+        eeprom_write_dword((uint32_t*)200, val);
+    }
+    /* Check values pre-compaction */
+    EEPROM_Init();
+    EXPECT_EQ(eeprom_read_dword((uint32_t*)0), 0xdeadbeef);
+    EXPECT_EQ(eeprom_read_byte((uint8_t*)4), 0x3c);
+    EXPECT_EQ(eeprom_read_word((uint16_t*)6), 0xd00d);
+    EXPECT_EQ(eeprom_read_dword((uint32_t*)150), 0xcafef00d);
+    EXPECT_EQ(eeprom_read_dword((uint32_t*)200), val);
+    EXPECT_NE(*(uint16_t*)&FlashBuf[LOG_BASE], 0xFFFF);
+    EXPECT_NE(*(uint16_t*)&FlashBuf[LOG_BASE + LOG_SIZE - 2], 0xFFFF);
+    /* Run compaction */
+    eeprom_write_byte((uint8_t*)4, 0x1f);
+    EEPROM_Init();
+    EXPECT_EQ(eeprom_read_dword((uint32_t*)0), 0xdeadbeef);
+    EXPECT_EQ(eeprom_read_byte((uint8_t*)4), 0x1f);
+    EXPECT_EQ(eeprom_read_word((uint16_t*)6), 0xd00d);
+    EXPECT_EQ(eeprom_read_dword((uint32_t*)150), 0xcafef00d);
+    EXPECT_EQ(eeprom_read_dword((uint32_t*)200), val);
+    EXPECT_EQ(*(uint16_t*)&FlashBuf[LOG_BASE], 0xFFFF);
+    EXPECT_EQ(*(uint16_t*)&FlashBuf[LOG_BASE + LOG_SIZE - 2], 0xFFFF);
+}
diff --git a/tmk_core/common/test/flash_stm32_mock.c b/tmk_core/common/test/flash_stm32_mock.c
new file mode 100644
index 0000000000..1b81d81f9a
--- /dev/null
+++ b/tmk_core/common/test/flash_stm32_mock.c
@@ -0,0 +1,50 @@
+/* Copyright 2021 by Don Kjer
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <string.h>
+#include <stdbool.h>
+#include "flash_stm32.h"
+
+uint8_t FlashBuf[MOCK_FLASH_SIZE] = {0};
+
+static bool flash_locked = true;
+
+FLASH_Status FLASH_ErasePage(uint32_t Page_Address) {
+    if (flash_locked) return FLASH_ERROR_WRP;
+    Page_Address -= (uintptr_t)FlashBuf;
+    Page_Address -= (Page_Address % FEE_PAGE_SIZE);
+    if (Page_Address >= MOCK_FLASH_SIZE) return FLASH_BAD_ADDRESS;
+    memset(&FlashBuf[Page_Address], '\xff', FEE_PAGE_SIZE);
+    return FLASH_COMPLETE;
+}
+
+FLASH_Status FLASH_ProgramHalfWord(uint32_t Address, uint16_t Data) {
+    if (flash_locked) return FLASH_ERROR_WRP;
+    Address -= (uintptr_t)FlashBuf;
+    if (Address >= MOCK_FLASH_SIZE) return FLASH_BAD_ADDRESS;
+    uint16_t oldData = *(uint16_t*)&FlashBuf[Address];
+    if (oldData == 0xFFFF || Data == 0) {
+        *(uint16_t*)&FlashBuf[Address] = Data;
+        return FLASH_COMPLETE;
+    } else {
+        return FLASH_ERROR_PG;
+    }
+}
+
+FLASH_Status FLASH_WaitForLastOperation(uint32_t Timeout) { return FLASH_COMPLETE; }
+void         FLASH_Unlock(void) { flash_locked = false; }
+void         FLASH_Lock(void) { flash_locked = true; }
+void         FLASH_ClearFlag(uint32_t FLASH_FLAG) {}
diff --git a/tmk_core/common/test/rules.mk b/tmk_core/common/test/rules.mk
new file mode 100644
index 0000000000..e47e5880c5
--- /dev/null
+++ b/tmk_core/common/test/rules.mk
@@ -0,0 +1,23 @@
+eeprom_stm32_DEFS  := -DFLASH_STM32_MOCKED -DNO_PRINT -DFEE_FLASH_BASE=FlashBuf
+eeprom_stm32_tiny_DEFS := $(eeprom_stm32_DEFS) \
+	-DFEE_MCU_FLASH_SIZE=1 \
+	-DMOCK_FLASH_SIZE=1024 \
+	-DFEE_PAGE_SIZE=512 \
+	-DFEE_DENSITY_PAGES=1
+eeprom_stm32_large_DEFS := $(eeprom_stm32_DEFS) \
+	-DFEE_MCU_FLASH_SIZE=64 \
+	-DMOCK_FLASH_SIZE=65536 \
+	-DFEE_PAGE_SIZE=2048 \
+	-DFEE_DENSITY_PAGES=16
+
+eeprom_stm32_INC := \
+	$(TMK_PATH)/common/chibios/
+eeprom_stm32_tiny_INC := $(eeprom_stm32_INC)
+eeprom_stm32_large_INC := $(eeprom_stm32_INC)
+
+eeprom_stm32_SRC := \
+	$(TMK_PATH)/common/test/eeprom_stm32_tests.cpp \
+	$(TMK_PATH)/common/test/flash_stm32_mock.c \
+	$(TMK_PATH)/common/chibios/eeprom_stm32.c
+eeprom_stm32_tiny_SRC := $(eeprom_stm32_SRC)
+eeprom_stm32_large_SRC := $(eeprom_stm32_SRC)
diff --git a/tmk_core/common/test/testlist.mk b/tmk_core/common/test/testlist.mk
new file mode 100644
index 0000000000..51a9638bb9
--- /dev/null
+++ b/tmk_core/common/test/testlist.mk
@@ -0,0 +1 @@
+TEST_LIST += eeprom_stm32_tiny eeprom_stm32_large