How to read characteristic value

[lyrics]

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]

You may read characteristic from your gatt evt handle like this.

void ble_gatt_c_on_ble_evt(ble_evt_t const * p_ble_evt, void * p_context)
{
if ((p_context == NULL) || (p_ble_evt == NULL))
{
return;
}

ble_gatt_c_t * p_ble_gatt_c = (ble_gatt_c_t *)p_context;

switch (p_ble_evt->header.evt_id)
{
case BLE_GATTC_EVT_HVX:
on_hvx(p_ble_gatt_c, p_ble_evt);
break;

case BLE_GATTC_EVT_CHAR_VAL_BY_UUID_READ_RSP:

on_read_rsp(p_ble_gatt_c, p_ble_evt);
break;

case   BLE_GATTC_EVT_WRITE_RSP:

on_write_rsp(p_ble_gatt_c, p_ble_evt);
break;

case BLE_GAP_EVT_DISCONNECTED:
on_disconnected(p_ble_gatt_c, p_ble_evt);
break;

default:
break;
}
}

In on_read_rsp code

evt->gattc_evt.params.char_val_by_uuid_read_rsp.handle_value[?]

to get your data.

By the way, your GAP service uuid=0x1601.

should be setup in your handle initial.

[Edvin]

Have you tried to debug and see what the data in the p_read_rsp->data looks like? What is the p_read_rsp->offset when you hit this for-loop?

[lyrics]

Hi, Edvin

Edvin said:

What is the p_read_rsp->offset when you hit this for-loop?

I just don't understand what offset means, so I tried 'for-loop'.

Edvin said:

Have you tried to debug and see what the data in the p_read_rsp->data looks like?

When I tried to see my device name which is 'MyService',

I can see my device name through 'p_read_rsp->data'.

 The picture is the result below.

case BLE_GATTC_EVT_CHAR_VAL_BY_UUID_READ_RSP :
    printf("Read length: %d, Read offset: %d\r\n", p_read_rsp->len, p_read_rsp->offset);
    printf("Read %d\r\n", p_read_rsp->data);
           
    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;

(I don't understand why offset fits the length of the data...)

I tried to show the characteristic value, just like the name but it's not coming out properly.

[lyrics]

Hi, Henry

The 'ble_app_uart_c' example does not have 'on_read_rsp', so I compiled the code.

Henry_Chou said:

evt->gattc_evt.params.char_val_by_uuid_read_rsp.handle_value[?]

ble_gattc_evt_read_rsp_t const * p_read_rsp = &p_ble_evt->evt.gattc_evt.params.read_rsp;

I tried to access value with 'p_read_rsp' by defining like this.

[Henry_Chou]

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