为什么我的 Flash 控制寄存器在我写入时没有更新（STM32）？

Question

I'm trying to write to update my engineering bytes on the STM32G0 and I'm getting stuck. I need to unlock flash by writing to the FLASH_KEYR register. The manual says this:

After reset, write into the FLASH control register (FLASH_CR) is not allowed so as to protect the Flash memory against possible unwanted operations due, for example, to electric disturbances. The following sequence unlocks these registers:

1. Write KEY1 = 0x4567 0123 in the FLASH key register (FLASH_KEYR)
2. Write KEY2 = 0xCDEF 89AB in the FLASH key register (FLASH_KEYR).

Any wrong sequence will lock the FLASH_CR registers until the next system reset. In the case of a wrong key sequence, a bus error is detected and a Hard Fault interrupt is generated.
The FLASH_CR registers can be locked again by software by setting the LOCK bit in one of these registers.

Note: The FLASH_CR register cannot be written when the BSY1 bit of the FLASH status register (FLASH_SR) is set. Any attempt to write to this register with the BSY1 bit set causes the AHB bus to stall until the BSY1 bit is cleared.

I making sure that my BSY1 bit is clear when I'm trying to write and I believe that's the only condition.

This is how I'm writing:

#define KEY1  0x45670123
#define KEY2  0xCDEF89AB

... 

FLASH->KEYR = KEY1;
FLASH->KEYR = KEY2;

After this point, my FLASH_KEYR register is still 0x0. Does anyone know why?

Edit: here's my code

        #define TEST_FLASH_BYTES    ((uint32_t)0x0801FF00)

        ...

        FLASH->CR &= FLASH_CR_LOCK;
        FLASH->KEYR = KEY1;
        FLASH->KEYR = KEY2;

        while(__HAL_FLASH_GET_FLAG(FLASH_SR_BSY1) != 0) {}

        program_flash(TEST_FLASH_BYTES, 0x1234567887654321);

        while (__HAL_FLASH_GET_FLAG(FLASH_SR_BSY1) != 0) {}

        FLASH->SR &= FLASH_SR_EOP;
        FLASH->CR &= FLASH_CR_PG;

here is program_flash :

static void program_flash(uint32_t address, uint64_t data)
{
    *(uint32_t *)address = (uint32_t)data;

    (independently of compiler optimization behavior) */
    __ISB();

    *(uint32_t *)(address + 4U) = (uint32_t)(data >> 32U);
}

Edit: it's a write only register so that's why I can't read it back. I figured out how to write to my memory successfully.

Answer 1

This code enables the boot0 pin to work like a legacy stm32 chip.

    //enable BOOT0 pin
    while(GET32(0x40022010)&0x10000) continue;
    PUT32(0x40022008,0x45670123);
    PUT32(0x40022008,0xCDEF89AB);
    PUT32(0x4002200C,0x08192A3B);
    PUT32(0x4002200C,0x4C5D6E7F);
//from the manual:
//ST production value: 0xDFFF E1AA
    PUT32(0x40022020,0xDEFFE1AA);
    while(GET32(0x40022010)&0x10000) continue;
    PUT32(0x40022014,0x00020000);
    while(GET32(0x40022010)&0x10000) continue;

PUT32 does an str instruction and GET32 does an ldr instruction.

The different STM32G0 have different default values for some of these registers, the one I have open right now for the FLASH_CR register is:

Reset value: 0xC000 0000

which is the two lock bit, so each of the unlock sequences above are tied to one bit, so do both sequences and in theory both bits unlock. May dig out a board/chip and try this and edit this answer to confirm.

It looks like you are doing this from a program, these chips are quite picky, with the flash erased (as in a new chip) you get one shot at the bootloader approach to loading, once something is there, then you can come in through SWD (I assume there is a way to block that), but you can't use swd to write these registers to perform these kinds of tasks you have to run code, and you can run it from ram or flash.

Depending what you are trying to change you may need to power cycle the chip to see the change take effect.

EDIT

while(GET32(0x40022010)&0x10000) continue; //need this here?
ra=GET32(0x40022014); //FLASH_CR
while(GET32(0x40022010)&0x10000) continue;
PUT32(0x40022008,0x45670123);
PUT32(0x40022008,0xCDEF89AB);
rb=GET32(0x40022014); //FLASH_CR
PUT32(0x4002200C,0x08192A3B);
PUT32(0x4002200C,0x4C5D6E7F);
rc=GET32(0x40022014); //FLASH_CR
hexstring(ra);
hexstring(rb);
hexstring(rc);

uart output

C0000000 
40000000 
00000000 

Which as expected from the documentation.

How and when are you reading the register? Are you touching any registers in between unlock and read?

Answer 2

I guess you did not enable the dugital FLASH intrface.

RCC -> AHBENR |= RCC_AHBENR_FLASHEN;

then

wait for the FLASH peripheral

while (FLASH -> SR & FLASH_SR_BSY1) ;

        RCC -> AHBENR |= RCC_AHBENR_FLASHEN;
        (*void)RCC -> AHBENR; // readback instead of delay to let this change to propagate throut the bus.
        while(FLASH -> SR & FLASH_SR_BSY1));
        //FLASH->CR &= FLASH_CR_LOCK; this line is worng. First of all it is not the way of reseting the bits, Secondly this bit is SET ONLY which meand that you can set it to enable the lock again
        FLASH->KEYR = KEY1;
        FLASH->KEYR = KEY2;

        while(FLASH -> SR & FLASH_SR_BSY1));