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simple_eeprom.h

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+#ifndef __SIMPLE_EEPROM_H
+#define __SIMPLE_EEPROM_H
+
+#include <stdbool.h>
+#include <stdint.h>
+
+#include "ch32v003fun.h"
+
+// config
+#define EEPROM_PAGE_SIZE 64     // size in bytes
+#define EEPROM_HALFWORD_SIZE 2  // size of halfword in bytes
+#define EEPROM_MAX_ENTRIES (EEPROM_PAGE_SIZE / EEPROM_HALFWORD_SIZE)
+
+typedef enum {
+  EEPROM_OK = 0,
+  EEPROM_ERROR_WRITE,
+  EEPROM_ERROR_ERASE,
+  EEPROM_ERROR_VERIFY
+} eeprom_status_t;
+
+// ######## internal variables
+//  import from .ld, halal by
+//  https://sourceware.org/binutils/docs/ld/Source-Code-Reference.html
+extern char _reserved_nv_start[];
+extern char _reserved_nv_end[];
+
+#define EEPROM_BASE (FLASH_BASE + (uint32_t)(uintptr_t)_reserved_nv_start)
+
+static void flash_unlock(void) {
+  if (FLASH->CTLR & 0x80) {
+    FLASH->KEYR = FLASH_KEY1;
+    FLASH->KEYR = FLASH_KEY2;
+  }
+}
+
+static void flash_lock(void) { FLASH->CTLR = 0x80; }
+
+static void flash_unlock_fast_mode(void) {
+  if (FLASH->CTLR & 0x8000) {
+    FLASH->MODEKEYR = FLASH_KEY1;
+    FLASH->MODEKEYR = FLASH_KEY2;
+  }
+}
+
+static void flash_wait_busy(void) { while (FLASH->STATR & FLASH_STATR_BSY); }
+
+static eeprom_status_t flash_erase_page(void) {
+  uint16_t *page_addr = (uint16_t *)EEPROM_BASE;
+
+  flash_unlock_fast_mode();
+  flash_wait_busy();
+
+  // erase page
+  FLASH->CTLR = CR_PAGE_ER;
+  FLASH->ADDR = (uint32_t)page_addr;
+  FLASH->CTLR = CR_STRT_Set | CR_PAGE_ER;
+  flash_wait_busy();
+
+  // verify erase
+  for (int i = 0; i < EEPROM_MAX_ENTRIES; i++) {
+    if (page_addr[i] != 0xFFFF) {
+      return EEPROM_ERROR_ERASE;
+    }
+  }
+
+  // disable fast mode
+  FLASH->CTLR = 0x8000;
+  return EEPROM_OK;
+}
+
+static int find_next_free_slot(void) {
+  uint16_t *word = (uint16_t *)EEPROM_BASE;
+  for (int i = 0; i < EEPROM_MAX_ENTRIES; i++) {
+    if (word[i] == 0xFFFF) {  // look for erased entries
+      return i;
+    }
+  }
+  return EEPROM_MAX_ENTRIES;
+}
+
+eeprom_status_t eeprom_write(uint16_t data) {
+  flash_unlock();
+
+  // find next available slot
+  int slot = find_next_free_slot();
+  uint16_t *word = (uint16_t *)EEPROM_BASE + slot;
+
+  // page is full, erase it
+  if (slot >= EEPROM_MAX_ENTRIES) {
+    eeprom_status_t status = flash_erase_page();
+    if (status != EEPROM_OK) {
+      flash_lock();
+      return status;
+    }
+    word = (uint16_t *)EEPROM_BASE;  // reset to start of page
+  }
+
+  // write data
+  FLASH->CTLR = CR_PG_Set;
+  *word = data;  // write full 16-bit value
+  flash_wait_busy();
+
+  // verify write
+  if (*word != data) {
+    flash_lock();
+    return EEPROM_ERROR_VERIFY;
+  }
+
+  flash_lock();
+  return EEPROM_OK;
+}
+
+uint16_t eeprom_read(void) {
+  uint16_t *word =
+      (uint16_t *)(EEPROM_BASE + EEPROM_PAGE_SIZE - EEPROM_HALFWORD_SIZE);
+
+  // scan back from the end until we find a non-erased value
+  for (int i = 0; i < EEPROM_MAX_ENTRIES; i++) {
+    uint16_t val = *word;
+    if (val != 0xFFFF) {
+      return val;
+    }
+    word--;
+  }
+
+  return 0xFFFF;  // nothing found
+}
+
+eeprom_status_t eeprom_init(void) {
+  uint16_t *page = (uint16_t *)EEPROM_BASE;
+
+  // check empty/partial page
+  bool needs_erase = true;
+  for (int i = 0; i < EEPROM_MAX_ENTRIES; i++) {
+    if (page[i] != 0xFFFF) {
+      needs_erase = false;
+      break;
+    }
+  }
+
+  if (needs_erase) {
+    return flash_erase_page();
+  }
+
+  return EEPROM_OK;
+}
+
+eeprom_status_t eeprom_wipe(void) { return flash_erase_page(); }
+
+#endif