EEPROM library

[schwinn]

Hello,

I noticed the high latency on EEPROM.read() requests on my STM32F407 and I had a look into EEPROM.h and stm32_eeprom.c.

So EEPROM.read() executes eeprom_read_byte() which is this function.

uint8_t eeprom_read_byte(const uint32_t pos)
{
#if defined(DATA_EEPROM_BASE)
  __IO uint8_t data = 0;
  if (pos <= (DATA_EEPROM_END - DATA_EEPROM_BASE)) {
    /* with actual EEPROM, pos is a relative address */
    data = *(__IO uint8_t *)(DATA_EEPROM_BASE + pos);
  }
  return (uint8_t)data;
#else
  eeprom_buffer_fill();
  return eeprom_buffered_read_byte(pos);
#endif /* _EEPROM_BASE */
}

My STM32 does not have a buildin EEPROM, so the #else Part is used every time and it show, that on every read eeprom_buffer_fill(); is called. This means the complete buffer of 8129 bytes is copied into RAM on every EEPROM.read call, which causes the latency. The eeprom_buffer_fill() takes 1208 microseconds on a STM32F407 with 48Mhz.

Is this intentional, and if so, is there a reason for it?

Thanks,
Thorsten

[fpistm]

You can refer to the wiki:
https://github.com/stm32duino/Arduino_Core_STM32/wiki/API#EEPROM-Emulation
And this example.
EEPROM is an emulation in flash so it is dependent of the FLASH constraint.