how erase flash memory only N bytes?

[lyrics]

Hi, all

I'm trying to write/erase data to flash memory (nrf52833, pca10100)

I want to erase only 4 bytes.. Is it wrong to define like this? I guess '4' value's unit is not bytes.  

        ret_code_t rc = nrf_fstorage_erase(&fstorage, now_addr, 4, NULL);
        APP_ERROR_CHECK(rc);
        wait_for_flash_ready(&fstorage);
        NRF_LOG_INFO("Done.");

I write code like above, but didn't work what I expected,

so I changed 'erase unit' 4096 to 4.. (in nrf_fstorage_sd.c)

/* Flash device information. */
static nrf_fstorage_info_t m_flash_info =
{
#if   defined(NRF51)
    .erase_unit   = 1024,
#elif defined(NRF52_SERIES)
//    .erase_unit   = 4,
    .erase_unit   = 4096,
#endif
    .program_unit = 4,
    .rmap         = true,
    .wmap         = false,
};

but it returns 0x03 error in fstorage_evt_handler function.

I don't know which part to modify more.

I'd appreciate it if you could suggest other methods than the ones above.

BR,

lyrics

[Kenneth]

Hi,

It's not possible to erase individual bytes, you need to erase a flash page. A page is 4096bytes.

Have in mind that when calling nrf_fstorage_erase() you specify the flash page address you want to erase, not the memory address.

Kenneth 

[lyrics]

Hi, thank you for reply..

So change the erase unit 4096 to 4 does not work.. right?

Kenneth said:

Have in mind that when calling nrf_fstorage_erase() you specify the flash page address you want to erase, not the memory address.

and can you explain more about this? What is different between flash page address and memory address? 

I though erasing flash page address is same as erasing memory.

I mean.. I want to erase(or write) data in flash memory, and is it right to use 'nrf_fstorage_earse()' function?

[Kenneth]

https://infocenter.nordicsemi.com/topic/ps_nrf52833/chapters/memory/doc/image/mem.svg

So page 0 start from 0x00000000-0x00001000, page 1 from 0x00001000-0x00002000, ..., page127 0x0007F000.

So if you want to erase memory in 0x00002nnnn, then you need to erase page 2.

Kenneth