Fstorage can only write max 11 bytes? Gives error when I write more than 11 bytes.

[kian79]

I am trying to use the fstorage library to store some data for my application and use the flash_fstorage example in SDK16 as a starting point and copied the required codes to my application.

I have to following array declared and called the nrf_fstorage_write function:

static char rx_data[] = "12345678901";

rc = nrf_fstorage_write(&fstorage, 0x3e000, rx_data, sizeof(rx_data), NULL);
APP_ERROR_CHECK(rc);
wait_for_flash_ready(&fstorage);
NRF_LOG_INFO("Done.");

This works well. There is 11 bytes in the array but I am not sure why the log gives: 

--> Event received: wrote 12 bytes at address 0x3E000.

If I change rx_data[] to a larger size, eg static char rx_data[] = "123456789012", it gives the following error:

<error> nrf_fstorage: !(len % p_fs->p_flash_info->program_unit) check failed in nrf_fstorage_write() with value 0x9.
<error> app: ERROR 9 [NRF_ERROR_INVALID_LENGTH] at D:\Nordic\nRF5_SDK_16.0.0\examples\ble_peripheral\ble_app_uart\main.c:1238
PC at: 0x000316AD

Anyone can advise? Thanks in advance.

[fhfs]

The array must be 32bits aligned see: nRF5_SDK_15_3_0\components\libraries\fstorage\nrf_fstorage.c:145 nRF5_SDK_15_3_0\components\libraries\fstorage\nrf_fstorage.h:260

[kian79]

Thanks. I just realised that too. But there is 11 bytes in the array why does it say wrote 12 bytes? Where is the additional byte coming from?

[Vidar Berg]

The string gets null-terminated ('\0'), hence the extra byte. Also, I would recommend using the __ALIGN(4) keyword when declaring the buffer to guarantee that the array always start at a word-aligned address.

__ALIGN(4) static char rx_data[]