RE: Read value from several characteristics as central to a custom service

maxx44 — Wed, 30 Mar 2022 01:35:58 GMT

Thanks Susheel.

This is somewhat helpful in that it tells me I have to resubmit the sd_ble_gattc_char_value_by_uuid_read() function. However it doesn't provide any details on how to implement the "updated handle range" in my code. My best guess was to use routines like my code snippet above for each characteristic.

This appears to be working. I am able to read the characteristic values for all 3 of my custom service characteristics. I implemented code to submit the sd_ble_gattc_char_value_by_uuid_read() for each characteristic, then used a timer to check the response had been handled. Then I launched the sd_ble_gattc_char_value_by_uuid_read() for the next characteristic. I can't claim this is a "good" solution, just that it seems to work. The SDK doesn't appear to have examples cover the ble central function to the extent of the ble peripheral functions.

Here's what I have in the ble event handler:

        case BLE_GATTC_EVT_CHAR_VAL_BY_UUID_READ_RSP:
            {
              if (temp_read)
                {             
                  ble_gattc_handle_value_t iter;
                  memset(&iter, 0, sizeof(ble_gattc_handle_value_t));
                  while (sd_ble_gattc_evt_char_val_by_uuid_read_rsp_iter(&p_ble_evt->evt.gattc_evt, &iter) == NRF_SUCCESS)
                   {
                     memcpy(temp_value, iter.p_value, p_ble_evt->evt.gattc_evt.params.char_val_by_uuid_read_rsp.value_len);
                   }
                   temp_read = false;
                }
              else if (hum_read)
                {             
                  ble_gattc_handle_value_t iter2;
                  memset(&iter2, 0, sizeof(ble_gattc_handle_value_t));
                  while (sd_ble_gattc_evt_char_val_by_uuid_read_rsp_iter(&p_ble_evt->evt.gattc_evt, &iter2) == NRF_SUCCESS)
                   {
                     memcpy(hum_value, iter2.p_value, p_ble_evt->evt.gattc_evt.params.char_val_by_uuid_read_rsp.value_len);
                   }
                   hum_read = false;
                }
              else if (vbatt_read)
                {             
                  ble_gattc_handle_value_t iter3;
                  memset(&iter3, 0, sizeof(ble_gattc_handle_value_t));
                  while (sd_ble_gattc_evt_char_val_by_uuid_read_rsp_iter(&p_ble_evt->evt.gattc_evt, &iter3) == NRF_SUCCESS)
                   {
                     memcpy(vbatt_value, iter3.p_value, p_ble_evt->evt.gattc_evt.params.char_val_by_uuid_read_rsp.value_len);
                   }
                   vbatt_read = false;
                }
              break;
            }

As can be seen, I used some boolean semaphore's to indicate a characteristic was handled and to move on to reading the next one.

It's still a work in progress, but I'm good with this for now. Hopefully this code might help someone grappling with the same problem despite the marginal coding style.

Cheers!

Max

RE: Read value from several characteristics as central to a custom service

Susheel Nuguru — Tue, 29 Mar 2022 08:53:23 GMT

From the documentation of sd_ble_gattc_char_value_by_uuid_read, it shows that you need to call the function again with an updated handle range if there are more characteristics in this service that need to be read.