nrf_fstorage not working

Question

Hello,

I am trying to use the **persistent** flash area of my nRF52.

I created a separate zone (PERSISTENT_FLASH) in my LD script as follows:

MEMORY
{
  FLASH (rx) : ORIGIN = 0x26000, LENGTH = 0x52000
  PERSISTENT_FLASH(rw): ORIGIN = 0x77000, LENGTH = 0x1000
  RAM (rwx) :  ORIGIN = 0x20002bf0, LENGTH = 0xd410
}

I try the following C code:

#define FSTORAGE_START  0x77000
#define FSTORAGE_LEN    0x01000

void callback(nrf_fstorage_evt_t * p_evt)
{
  NRF_LOG_DEBUG("callback");
}
NRF_FSTORAGE_DEF(nrf_fstorage_t my_instance) =
{
    .evt_handler    = callback,
    .start_addr     = FSTORAGE_START,
    .end_addr       = FSTORAGE_START + FSTORAGE_LEN,
};

void test_flash()
{
    ret_code_t rc;

    rc = nrf_fstorage_init(
        &my_instance,       /* You fstorage instance, previously defined. */
        &nrf_fstorage_sd,   /* Name of the backend. */
        NULL                /* Optional parameter, backend-dependant. */
    );
    NRF_LOG_DEBUG("1===> %d %s", rc, nrf_strerror_get(rc));

    char buf_i[] = "1234567890123456";
    rc = nrf_fstorage_write(
        &my_instance,   /* The instance to use. */
        FSTORAGE_START, /* The address in flash where to store the data. */
        buf_i,          /* A pointer to the data. */
        16,             /* Lenght of the data, in bytes. */
        NULL            /* Optional parameter, backend-dependent. */
    );
    NRF_LOG_DEBUG("2===> %d %s", rc, nrf_strerror_get(rc));

    char buf_o[24];
    rc = nrf_fstorage_read(
        &my_instance,       /* The instance to use. */
        FSTORAGE_START,     /* The address in flash where to read data from. */
        buf_o,              /* A buffer to copy the data into. */
        16                  /* Lenght of the data, in bytes. */
    );
    buf_o[16] = '\0';
    NRF_LOG_DEBUG("3===> %d %s `%s'", rc, nrf_strerror_get(rc), buf_o);
}

I get the following output:

00> <debug> app: 1===> 0 NRF_SUCCESS
00> <debug> app: callback
00> <debug> app: 2===> 0 NRF_SUCCESS
00> <debug> app: 3===> 0 NRF_SUCCESS `'

What am I missing here?

I am using SDK nRF5_SDK_17.0.2_d674dde, with softdevice s132_nrf52_7.2.0_softdevice.hex.

Thanks a lot!