I am using an STM32WLE5 in a design, in the user manual section 3.3.8 it specifically says:
Programming in a previously programmed double-word is only allowed when programming an all 0 value. It is not allowed to program any other value in a previously programmed double-word. Any attempt sets PROGERR flag in FLASH_SR, except when programming an already programmed double-word with an all 0 value.
In practice this is not working, I noticed the MCU differentiates between "virgin" all FF double word which is the erase state and a programmed all FF double word. I believe this is related to ECC but I would like to get more information about this if possible.
Below is a small code snippet that illustrates the test I am running:
uint8_t *addr = (uint8_t *) 0x08000800;
uint8_t zeroes[8] = {0};
uint8_t effs[8] = {0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,};
hal_flash_page_erase(addr); //Page erase to all FFs as expected
flash_write_dw(addr, effs); //Manually programming 1st dw as effs
flash_write_dw(addr+8, effs); //Manually programming 2nd dw as effs
flash_write_dw(addr+16, effs); //Manually programming 3rd dw as effs
flash_write_dw(addr+24, effs); //Manually programming 4th dw as effs
flash_write_dw(addr, zeroes); //Reprogram 1st dw as zeros, does not work
flash_write_dw(addr+8, zeroes); //Reprogram 2nd dw as zeros, does not work
flash_write_dw(addr+16, zeroes); //Reprogram 3rd dw as zeros, does not work
flash_write_dw(addr+24, zeroes); //Reprogram 4th dw as zeros, does not work
flash_write_dw(addr+32, zeroes); //Reprogram 5th dw as zeros, WORKS DW still erased
flash_write_dw(addr+40, zeroes); //Reprogram 6th dw as zeros, WORKS DW still erased
