How to read characteristic value

Question

Hi, all

I'm using nRF52832 pc10040, s132.

This is ble_app_uart_c example, and I'm trying to read my own beacon device's characteristic value.

ble_uuid_t p_uuid = {.uuid = 0x1601, .type = BLE_UUID_TYPE_BLE};
ble_gattc_handle_range_t p_handle_range = {.start_handle = 0x0001, .end_handle = 0xFFFF};

err_code = sd_ble_gattc_char_value_by_uuid_read(p_ble_nus_evt->conn_handle, &p_uuid, &p_handle_range);
            
if(err_code != NRF_SUCCESS)
{
    NRF_LOG_INFO("Failed to send read request to peer error = %d", err_code);
    printf("\n\rFailed to send read request to peer error = %d\n\r", err_code);
}

I successfully retrieved device name using line 4: 'sd_ble_gattc_char_value_by_uuid_read'.

I also read the value of '0' before my device sent data.

But if I try to read the moment the device sends data, I can't get the value right.

I have to read this type of value.

case BLE_GATTC_EVT_CHAR_VAL_BY_UUID_READ_RSP :
            for(uint32_t j = 0; j <=  p_read_rsp->len; j++) {
                for (uint32_t i = 0; i < p_read_rsp->offset; i++)
                {
                    while(app_uart_put( p_read_rsp->data[i]) != NRF_SUCCESS);
                }
                printf("\r\n");       
            }
            break;

this is my output part code.

How can I get this value?

Henry_Chou · Accepted Answer

Hey!Lyrics: 
 the ble_app_uart.c dosen't have the code exactly. The code is build in my project case. 
 However, you may take the reference code from SDK (Central or Peripheral) ble_app_gatts example. The gatt_cache_manager.c 
 void gcm_ble_evt_handler(ble_evt_t const * p_ble_evt) 
 function. case BLE_GATTC_EVT_READ_RSP: 
 You may get the answer which you need. However nus(Nordic Uart service) is also a kind of gatt. So the solution is the same. 
 My SDK version is 17.0.2

Edvin · Answer

Do you know what data the characteristic you are reading holds? Is it "E5 2F 46 C4 00 00 00"? Or is that just an example? It looks like you are trying to print them as numbers when you use %d, but when you use app_uart_put() it will print the hexadecimal value, so depending on your UART terminal, it may look different due to how it interprets non-ascii values. I am a bit confused by your parameter names. Where do you receive this event, and what parameters does that callback contain? The BLE_GATTC_EVT_CHAR_VAL_BY_UUID_READ_RSP event should contain something like a ble_evt_t, possibly called p_ble_evt, and it should contain: p_ble_evt-> gattc_evt . params. char_val_by_uuid_read_rsp.value_len and p_ble_evt-> gattc_evt . params. char_val_by_uuid_read_rsp.handle_value, but not "len". Where do you get this callback? And does your peripheral support reading and not only notifications? What is your peripheral? Is it something you wrote yourself? Is it running on a Nordic chip? Let us say that the event does contain a pointer to the data, "p_value", and a length variable "len". If your data contains ascii characters (only) you can use: NRF_LOG_RAW_INFO("received: "); for (uint8_t i=0; i

How to read characteristic value

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