Problem with Writing to the Flash Memory of the STM32L4R5 microcontroller - c++

Question

I'm trying to write to the flash memory of STM32L4R5 in 'FLASH_TYPEPROGRAM_FAST' mode of the HAL_FLASH_Program().
The flash of the MCU is configured as Single Bank.
Writing to the flash only works when using 'FLASH_TYPEPROGRAM_DOUBLEWORD'. The flash reads as 0xFFFFFFFF when written in 'FLASH_TYPEPROGRAM_FAST' mode.
This is my test project:
// Page Erase Structure
static FLASH_EraseInitTypeDef EraseInitStruct;
// Page Erase Status
uint32_t eraseStatus;
// Data Buffer
uint64_t pDataBuf[32] =
{
0x1111111122222222, 0x3333333344444444,
0x5555555566666666, 0x7777777788888888,
0x12345678ABC12345, 0x23456789DEF01234,
0x34567890AAABBB12, 0x4567890FABCDDD34,
0x1111111122222222, 0x3333333344444444,
0x5555555566666666, 0x7777777788888888,
0x12345678ABC12345, 0x23456789DEF01234,
0x34567890AAABBB12, 0x4567890FABCDDD34,
0x1111111122222222, 0x3333333344444444,
0x5555555566666666, 0x7777777788888888,
0x12345678ABC12345, 0x23456789DEF01234,
0x34567890AAABBB12, 0x4567890FABCDDD34,
0x1111111122222222, 0x3333333344444444,
0x5555555566666666, 0x7777777788888888,
0x12345678ABC12345, 0x23456789DEF01234,
0x34567890AAABBB12, 0x4567890FABCDDD34
};
// Flash Page Start Address
uint32_t pageAddr = 0x081FE000;
// Fill Erase Init Structure
EraseInitStruct.TypeErase = FLASH_TYPEERASE_PAGES;
EraseInitStruct.Banks = FLASH_BANK_1;
EraseInitStruct.Page = 255;
EraseInitStruct.NbPages = 1;
// Unlocking the FLASH Control Register
HAL_FLASH_Unlock();
// Clear OPTVERR Bit Set on Virgin Samples
__HAL_FLASH_CLEAR_FLAG(FLASH_FLAG_OPTVERR);
// Erasing the Flash Page
HAL_FLASHEx_Erase(&EraseInitStruct, &Error);
#if 0
// Wriring a Doubled Word to Flash. pDataBuf[0] is the 64-bit Word
HAL_FLASH_Program(FLASH_TYPEPROGRAM_DOUBLEWORD, pageAddr, pDataBuf[0]);
#else
// Wriring 32 Double Words. pDataBuf is the Starting Address of the 64-bit Array
HAL_FLASH_Program(FLASH_TYPEPROGRAM_FAST_AND_LAST, pageAddr, pDataBuf);
#endif
// Locking the FLASH Control Register
HAL_FLASH_Lock();
Am I doing anything wrong?
Thank you,
Ivan

Answer 1

Document RM0932, Reference manual for STM32L4+, section FLASH. It covers reading and writing from/to flash, for both single-bank and double-bank configurations and different MCU models of this line. It seems, most differences are about reading from Flash (64-bit for dual bank, 128-bit for single bank). As for writing, page 128:
Flash is very picky about data width, and every STM32 has different data width for its flash, it seems. Very recently I stumbled upon one, which accepted only 16-bit writes and reads. This one likes double words. There is no universal function to read and write flash to any STM32, so it seems one of your commands doesn't respect this MCU's Flash data width rules. You can check if any error flags appear as per reference manual, although, as you can see, it doesn't say anything about trying to write 32-bit piece of data. I would expect that write to fail, but we can't make any conclusions about error flags from the screenshot provided. If you're curious enough, you can look at what data width every mode/function of yours utilizes and see what happens. 64-bit writes have to work.