Reading From internal Flash of STM32Fxxx

In this guide, we shall see how to read data from the internal flash storage of STM32Fxxx (tested on STM32F1 and F4).

In this guide, we shall cover the following:

• Internal Flash Storage of STM32F411.
• Develop the driver.
• Code.
• Results.

1. Internal Flash Storage of STM32F411:

The Flash memory interface manages CPU AHB I-Code and D-Code accesses to the Flash memory. It implements the erase and program Flash memory operations and the read and write protection mechanisms.

The Flash memory interface accelerates code execution with a system of instruction prefetch and cache lines.

Main features

• Flash memory read operations

• Flash memory program/erase operations

• Read / write protections

• Prefetch on I-Code

• 64 cache lines of 128 bits on I-Code

• 8 cache lines of 128 bits on D-Code

Figure below shows the Flash memory interface connection inside the system architecture.

The Flash memory has the following main features:

• Capacity up to 512 KBytes for STM32F411xC/E

• 128 bits wide data read

• Byte, half-word, word and double word write

• Sector and mass erase

• Memory organization The Flash memory is organized as follows:

– A main memory block divided into 4 sectors of 16 KBytes, 1 sector of 64 KBytes, 3 sectors of 128 Kbytes (STM32F411xC/E).

– System memory from which the device boots in System memory boot mode

– 512 OTP (one-time programmable) bytes for user data The OTP area contains 16 additional bytes used to lock the corresponding OTP data block.

– Option bytes to configure read and write protection, BOR level, watchdog software/hardware and reset when the device is in Standby or Stop mode.

• Low-power modes (for details refer to the Power control (PWR) section of the reference manual)

Figure below shows the flash storage organization within STM32F411:

2. Developing the Driver:

We start off by creating new source and header file with name of flash.c and flash.h respectively.

Within the header, include stdint as following:

#include "stdint.h"

Declare the following function:

void flash_read32(uint32_t addrs, uint32_t *rd32, uint32_t len);

The function takes three arguments:

• The address to be read.
• pointer to hold the read address.
• Length to be read.

And the function returns nothing.

Within source code, include the flash.h and stm32f4xx.h header files as following:

#include "Flash.h"
#include "stm32f4xx.h"

For the function to read from flash:

void flash_read32(uint32_t addrs, uint32_t *rd32, uint32_t len)
{

Within the function:

Store the passed address into temporary variable:

uint32_t tempAddrs = addrs;

Declare a for loop starts from 0 to the length:

for(uint32_t i=0; i<len; i++)

Within the loop:

rd32[i] = *(__IO uint32_t*) tempAddrs;

convert the temporary variable into pointer then dereference the pointer and store the read memory location into rd32 array.

Increment the address by 4 since the datawidth is 4byte:

tempAddrs+=4;

close the function:

}

Hence, the function as following:

void flash_read32(uint32_t addrs, uint32_t *rd32, uint32_t len)
{
  //Read data can be accessed straight away
  uint32_t tempAddrs = addrs;

  for(uint32_t i=0; i<len; i++)
  {
    rd32[i] = *(__IO uint32_t*) tempAddrs;
    tempAddrs+=4;
  }
}

Within main.c file:

#include "stdio.h"
#include "delay.h"
#include "flash.h"
#include "uart.h"

uint32_t flash_data[4];


int main(void)
{
	uart2_tx_init(115200,16000000);
	systick_init_ms(16000000);
	flash_read32(0x08000000,flash_data,4);
	printf("First 4 word data in flash are:\r\n");
	for (int i=0;i<4;i++)
	{
		printf("%d -> 0x%x\r\n",i,flash_data[i]);
	}

	while(1)
	{



	}
}

3. Code:

You may download the entire source code from here:

4. Results:

Successfully Read the first 16 Bytes of the flash storage.

Happy coding 🙂