sd_ble_gatts_value_set causes a segmentation violation (SIGSEGV)

[SergeyK]

I'm trying to create a simple service that would just provide some data which could get updated internally (for example, via SPI bus). Data may be of a different size, so I'm trying to notify the device about the change in data buffer by calling sd_ble_gatts_value_set. However, I get a SIGSEGV when I call that function. Here's how I set up a service:



ble_uuid_t ble_uuid;

ble_gatts_char_md_t char_md;
ble_gatts_attr_md_t attr_md;
ble_gatts_attr_t attr_char_value;
...
char_md.char_props.read = 1;
char_md.char_props.write = 0;
char_md.char_props.notify = 0;

BLE_GAP_CONN_SEC_MODE_SET_OPEN(&attr_md.read_perm);
BLE_GAP_CONN_SEC_MODE_SET_NO_ACCESS(&attr_md.write_perm);
attr_md.vloc = BLE_GATTS_VLOC_STACK;
attr_md.rd_auth = 0;
attr_md.wr_auth = 0;
attr_md.vlen = 1;

attr_char_value.p_uuid = &ble_uuid;
attr_char_value.p_attr_md = &attr_md;
attr_char_value.init_len = 1;
attr_char_value.init_offs = 0;
attr_char_value.max_len = 256;
attr_char_value.p_value = data; // data is a pointer to the buffer

err_code = sd_ble_gatts_characteristic_add(
  p_service->service_handle,
  &char_md, &attr_char_value,
  &p_service->char_handle
);

VERIFY_SUCCESS(err_code);

I tried setting attr_md.vloc to either BLE_GATTS_VLOC_STACK or BLE_GATTS_VLOC_USER, depending on whether I was allocating arrays on stack or on heap - I have tried both, with both using malloc and nrf_malloc.
Then I change a data in the buffer and I would like to update the length of the data:

ble_gatts_value_t value_md = {
 .len = length, // length is passed to the function 
 .offset = 0,
 .p_value = NULL
};
err_code = sd_ble_gatts_value_set(
 BLE_CONN_HANDLE_INVALID,
 p_service->char_handles.value_handle,
 &value_md
);
VERIFY_SUCCESS(err_code);

return NRF_SUCCESS

I suspect I have some issues with allocating my buffers, or I don't understand something about what data exactly is in the Characteristic, because when I try to just change the first byte of the data array in the code after I have created the service and characteristics, I don't see an update in the nRF Connect app, but if I set it beforehand, I can see it.

Please tell me if I can provide any other code snippets or sdk configuration information if that would help you help me solve this problem. My SDK version is 7.0.1.

Thanks in advance for all suggestions.