STM32 FLASH Page Write Protection

Brian1 · ‎2010-07-01

Posted on July 01, 2010 at 20:49

#stm32 #stm32

Brian1 · ‎2011-05-17

Posted on May 17, 2011 at 13:57

Thanks for the suggestion. I found an STMicro example provided with my IAR install that seems pretty close to what I need. My version of the code is shown below. The problem I'm having now is that the FLASH_EnableWriteProtection function is failing, with a status of FLASH_ERROR_PG, when trying to write protect the specific pages. Not sure if there is something else I need to configure?

// Unlock the Flash Program Erase controller

FLASH_Unlock();

FLASH_ClearFlag(FLASH_FLAG_BSY | FLASH_FLAG_EOP| FLASH_FLAG_PGERR | FLASH_FLAG_WRPRTERR);

// Get pages write protection status

unsigned int WRPR_Value = FLASH_GetWriteProtectionOptionByte();

unsigned int ProtectedPages = WRPR_Value & 0x0000000F; // (FLASH_WRProt_Pages0to1 | FLASH_WRProt_Pages2to3 |

// FLASH_WRProt_Pages4to5 | FLASH_WRProt_Pages6to7)

// Pages are not write protected

if (ProtectedPages != 0x00)

{

// protect bootloader FLASH area

FLASH_EnableWriteProtection(FLASH_WRProt_Pages0to1 | FLASH_WRProt_Pages2to3 |

FLASH_WRProt_Pages4to5 | FLASH_WRProt_Pages6to7);

// Generate System Reset to load the new option byte values

NVIC_GenerateSystemReset();

}

FLASH_Lock();

swhite2 · ‎2011-05-17

Posted on May 17, 2011 at 13:57

Try putting

FLASH_Unlock();

before your line and

FLASH_Lock();

after it. The flash controller prevents updates unless enabled. The write protect bits are in flash so...

swhite2 · ‎2011-05-17

Posted on May 17, 2011 at 13:57

The flash write-protect bits are stored in flash and hence need to be erased before writing if there's any 0->1 transitions.

Those bits are in the option bytes area of flash and this has its own erase function

FLASH_EraseOptionBytes()

The trouble with that is that it erases ALL option bytes so you have to write your own function to save the existing option bytes, program the write-protect bits and then reprogram the other option bytes.

I suggest you read the

http://www.st.com/stonline/products/literature/pm/13259.pdf

manual (all of it).

damh · ‎2011-05-17

Posted on May 17, 2011 at 13:57

The flash write-protect bits are stored in flash and hence need to be erased before writing if there's any 0->1 transitions.

It is more worse. Every 16 bit of the option byte area can only be written one time after an erase command to the option byte flash.

The option bytes have a ''xor check sum'' in each following byte:

option byte

check sum

option byte

check sum

...

Even if the flash could change single bits (STMs flash in STM32f1xx can NOT), the check sums would prevent.

Brian1 · ‎2011-05-17

Posted on May 17, 2011 at 13:57

Thanks for the suggestions. Here is the code I ended up with. It seems to be working pretty well.

// unlock the Flash Program Erase Controller (FPEC)

FLASH_Unlock();

FLASH_ClearFlag(FLASH_FLAG_BSY | FLASH_FLAG_EOP| FLASH_FLAG_PGERR | FLASH_FLAG_WRPRTERR);

// get pages write protection status

unsigned int WRPR_Value = FLASH_GetWriteProtectionOptionByte();

unsigned int ProtectedPages = WRPR_Value & (FLASH_WRProt_Pages0to1 | FLASH_WRProt_Pages2to3 |

FLASH_WRProt_Pages4to5 | FLASH_WRProt_Pages6to7);

// pages are not write protected

if(ProtectedPages != 0x00)

{

// erase option bytes (must do this before writing option bytes)

FLASH_EraseOptionBytes();

// read protection needs to happen before write protection, since this

// function erases all option bytes

FLASH_ReadOutProtection(ENABLE);

// program user option bytes

FLASH_UserOptionByteConfig(OB_IWDG_SW, OB_STOP_NoRST, OB_STDBY_NoRST);

// protect bootloader FLASH area

FLASH_EnableWriteProtection(FLASH_WRProt_Pages0to1 | FLASH_WRProt_Pages2to3 |

FLASH_WRProt_Pages4to5 | FLASH_WRProt_Pages6to7);

// generate System Reset to load the new option byte values

NVIC_GenerateSystemReset();

}

// lock the Flash Program Erase Controller (FPEC)

FLASH_Lock();