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EEPROM emulation

EEPROM emulation is based on Arduino API: https://docs.arduino.cc/learn/built-in-libraries/eeprom/

Emulation is made in Flash, with all constraints related to Flash operation:

  • whole sector/page erased and written for each write operation. This can be very long depending on sector/page size.
  • limited Flash life cycle write operation

In addition to Arduino API, to mitigate Flash constraints, it is possible to use buffered API: Write operations are made in an intermediate RAM buffer, and only at the end (after writing several parameters for example) the buffer is copied in Flash. Thus only 1 write operation for a whole bunch of data. Example is available here: https://github.com/stm32duino/STM32Examples/tree/main/examples/NonReg/BufferedEEPROM 

void eeprom_buffer_fill(); // This function copies the data from flash into the buffer
void eeprom_buffer_flush(); // This function writes the buffer content into the flash
uint8_t eeprom_buffered_read_byte(const uint32_t pos); // Function reads a byte from the eeprom buffer
void eeprom_buffered_write_byte(uint32_t pos, uint8_t value); // Function writes a byte to the eeprom buffer
By default, EEPROM emulation storage correspond to the last sector/page of Flash, and its size correspond to the size of the last sector/page. Nevertheless it is possible to customize address and size used for EEPROM. In this case, following switches should be defined (in variant.h or build_opt.h)

  • FLASH_BASE_ADDRESS
  • FLASH_DATA_SECTOR or FLASH_PAGE_NUMBER (depending on STM32 family used)

see example of variant implementation: PR #938

Warning

Single/dual bank configuration:

Default last sector used correspond to default board configuration.

For example, NUCLEO_F767ZI is by default configured in single bank. Last sector correspond to this bank configuration. If this configuration is changed, it is then mandatory to customize FLASH_BASE_ADDRESS/FLASH_DATA_SECTOR, even to use last sector of Flash.