nRF51: writing to a characteristic

[mr91]

Hello,

I am using SD 130 on nRF5 with SDK V12.1.0.

I want to write to a characteristic using the android debug app (nrf connect).

This is my code for the characteristic:

  ble_uuid_t          char_uuid;
  char_uuid.uuid      = BLE_UUID_MY_CHARACTERISTC_UUID;
  err_code = sd_ble_uuid_vs_add(&base_uuid, &char_uuid.type);
  APP_ERROR_CHECK(err_code);



  ble_gatts_attr_md_t attr_md;
  memset(&attr_md, 0, sizeof(attr_md));
  attr_md.vloc        = BLE_GATTS_VLOC_STACK;              
  BLE_GAP_CONN_SEC_MODE_SET_OPEN(&attr_md.read_perm);       
  BLE_GAP_CONN_SEC_MODE_SET_OPEN(&attr_md.write_perm);      

  /* Characteristic Value Attribute  */
  ble_gatts_attr_t    attr_char_value;

  memset(&attr_char_value, 0, sizeof(attr_char_value));   
  attr_char_value.p_uuid      = &char_uuid;
  attr_char_value.p_attr_md   = &attr_md;                     /* assign attribute metadata to characteristic value attribute */
  attr_char_value.max_len     = 1;                            /* max value length */
  attr_char_value.init_len    = 1;                            /* initial value length */
  attr_char_value.p_value = (uint8_t*)&MyVar;                            /* ptr to actual value */


  ble_gatts_char_md_t char_md;
  memset(&char_md, 0, sizeof(char_md));
  char_md.char_props.read = 1;                                /* set read property */
  char_md.char_props.write = 1;                               /* set write proper */
  

  err_code = sd_ble_gatts_characteristic_add(p_our_service->service_handle,
                                     &char_md,
                                     &attr_char_value,
                                     &p_our_service->char_handles_dry);
  APP_ERROR_CHECK(err_code);

What is happening: I can write a value to the characteristic. When I read it afterwards, it is correct. BUT: The debugger shows me, that MyVar did not change.

Question 1: Where is the new value saved? It's obviously not in MyVar as I assumed.

Question 2: How can I update MyVar with the correct value?

Thank you very much in advance!

Regards

[Michael Antwih]

The code you show above will just setup the characteristic. You need to handle the writing of the value in the on_write function which is normally called by the on ble evt handler. The value might be wriiten to the stack by default which might be why you are able to read it back correctly. If you handle the on write for your char then you should be able to set the value of myvar.