[EEPROM] Add pseudo-EEPROM support for MP1 RETRAM

Author: kbumsik

cores/arduino/stm32/stm32_eeprom.c

@@ -39,6 +39,13 @@
 extern "C" {
 #endif
 
+#ifndef EEPROM_RETRAM_MODE  /* Buffering not needed in RETRAM mode */
+
+static void eeprom_buffer_fill();
+static void eeprom_buffer_flush();
+static uint8_t eeprom_buffered_read_byte(const uint32_t pos);
+static void eeprom_buffered_write_byte(uint32_t pos, uint8_t value);
+
 /* Be able to change FLASH_BANK_NUMBER to use if relevant */
 #if !defined(FLASH_BANK_NUMBER) &&\
     (defined(STM32F0xx) || defined(STM32F1xx) || defined(STM32G4xx) ||\
@@ -306,6 +313,37 @@ void eeprom_buffer_flush(void)
 #endif
 }
 
+#else /* EEPROM_RETRAM_MODE */
+/**
+  * @brief  Function reads a byte from emulated eeprom (flash)
+  * @param  pos : address to read
+  * @retval byte : data read from eeprom
+  */
+uint8_t eeprom_read_byte(const uint32_t pos)
+{
+  uint8_t tmp;
+  if (pos > E2END) {
+    return 0;
+  }
+  memcpy(&tmp, (uint8_t *)(EEPROM_RETRAM_START_ADDRESS + pos), sizeof(uint8_t));
+  return tmp;
+}
+
+/**
+  * @brief  Function writes a byte to emulated eeprom (flash)
+  * @param  pos : address to write
+  * @param  value : value to write
+  * @retval none
+  */
+void eeprom_write_byte(uint32_t pos, uint8_t value)
+{
+  if (pos > E2END) {
+    return;
+  }
+  memcpy((uint8_t *)(EEPROM_RETRAM_START_ADDRESS + pos), &value, sizeof(uint8_t));
+}
+#endif /* EEPROM_RETRAM_MODE */
+
 #ifdef __cplusplus
 }
 #endif

cores/arduino/stm32/stm32_eeprom.h

@@ -45,6 +45,31 @@ extern "C" {
 
 /* Exported types ------------------------------------------------------------*/
 /* Exported constants --------------------------------------------------------*/
+#if defined(STM32MP1xx)
+/* Note for STM32MP1xx devices:
+ * Those devices do not have non-volatile memory. The emulation is done
+ * in RETRAM. Therefore data will be preserved *only* when VBAT is supplied
+ * (e.g. A coin battery is connected to CN3 on STM32MP157A_DK1) and
+ * the coprocessor is waken up from STANBY mode.
+ * The data won't be preserved from cold boot, even if VBAT is connected.
+ * See: https://community.st.com/s/question/0D50X0000B44pHUSQY/doesnt-the-mcu-coprocessor-have-nonvolatile-memory
+ */
+#define EEPROM_RETRAM_MODE
+/* 4kB is the same size as EEPROM size of ATMega2560. */
+#ifndef EEPROM_RETRAM_MODE_SIZE
+#define EEPROM_RETRAM_MODE_SIZE ((uint32_t)(4*1024))
+#endif
+/* RETRAM start address is 0x00000000 (retset entry) and end address is
+ * 0x00020000 (64kB in total). The by default, ldscript.ld for STM32MP1xx
+ * does not define address between 0x00000298 (end of ISR Vector) and 0x00020000.
+ * So it is okay to use in this address range. Make sure ldscript.ld does not
+ * overrap the following address range.
+ */
+#ifndef EEPROM_RETRAM_START_ADDRESS
+#define EEPROM_RETRAM_START_ADDRESS (0x00000400UL)
+#endif
+#define E2END (EEPROM_RETRAM_MODE_SIZE - 1)
+#else
 #ifndef FLASH_PAGE_SIZE
 /*
  * FLASH_PAGE_SIZE is not defined for STM32F2xx, STM32F4xx and STM32F7xx
@@ -56,18 +81,14 @@ extern "C" {
 #define FLASH_PAGE_SIZE     ((uint32_t)(16*1024)) /* 16kB page */
 #endif
 #define E2END (FLASH_PAGE_SIZE - 1)
+#endif
 
 /* Exported macro ------------------------------------------------------------*/
 /* Exported functions ------------------------------------------------------- */
 
 uint8_t eeprom_read_byte(const uint32_t pos);
 void eeprom_write_byte(uint32_t pos, uint8_t value);
 
-void eeprom_buffer_fill();
-void eeprom_buffer_flush();
-uint8_t eeprom_buffered_read_byte(const uint32_t pos);
-void eeprom_buffered_write_byte(uint32_t pos, uint8_t value);
-
 #ifdef __cplusplus
 }
 #endif