BLE Server attribute value response truncation issue

[Ashvajit.P]

Hello

I am using ESP32 S3 with GATT server example. When I am sending read characteristic request from BLE client (ESP32 S3) then I am getting proper response as shown

BLE client log from ESP32 S3

ble_c_resp.PNG (29.92 KiB) Viewed 2901 times

But same request is sent form mobile app then I am getting same hex value dumped over 4-5 times and getting warning in the logs of my ESP32 S3 GATT SERVER

BLE Server log in ESP32 S3 when requested from app

ble.PNG (37.64 KiB) Viewed 2901 times

BLE server code snippet :

Code: Select all

#define GATTS_DEMO_CHAR_VAL_LEN_MAX 0xf0
static uint8_t BLE_payload[60] =  { 46, 197, 213, 196, 245,  22,  22,  98,130, 180, 185,  27, 212,  55, 243, 215, 135,  12,   2,  75,  16,  54, 218, 125, 183, 159,  35, 161, 215, 221,  97, 26, 110, 105,  64, 145, 228, 242,  80,  70, 156,  34, 121, 213,  49, 229, 199, 148, 134, 73};
static uint8_t BLE_buffer[22] = { 46, 197, 213, 196, 245, 22, 22, 98, 130, 180, 185, 27, 212, 55, 243, 215, 135, 12, 2, 75, 16 };
static esp_attr_value_t gatts_demo_char1_val =
{
    .attr_max_len = GATTS_DEMO_CHAR_VAL_LEN_MAX,
    .attr_len     = 60,
    .attr_value   = BLE_payload,
};

Code: Select all

  
    case ESP_GATTS_READ_EVT: {
        ESP_LOGI(GATTS_TAG, "GATT_READ_EVT, conn_id %d, trans_id %d, handle %d\n", param->read.conn_id, param->read.trans_id, param->read.handle);
        esp_gatt_rsp_t rsp;
        memset(&rsp, 0, sizeof(esp_gatt_rsp_t));
        rsp.attr_value.handle = param->read.handle;
        rsp.attr_value.len = 32;
        rsp.attr_value.value[0] = 0xde;
        rsp.attr_value.value[1] = 0xed;
        rsp.attr_value.value[2] = 0xbe;
        rsp.attr_value.value[3] = 0xef;
	    memcpy(rsp.attr_value.value, BLE_payload, 32);
        esp_ble_gatts_send_response(gatts_if, param->read.conn_id, param->read.trans_id,
                                    ESP_GATT_OK, &rsp);
        break;

Response observed on app

Screenshot from NRF connect app after sending read request

nrf_ss.jpeg (157.7 KiB) Viewed 2901 times

[chegewara]

I didnt check your code, but from NRF connect screenshot i can tell that you are sending incorrect value (characteristic value) on CCC descriptor request.

[Ashvajit.P]

Yes, but that is not the case with same data, wen requested from ESP module instead of the app

[chegewara]

1. your code is messed in many places, one i mentioned above, another is probably sending response on read request, which is not setting bit which tells its not whole value sent (due to MTU size)
2. i am guessing esp32 BLE client code is exchanging MTU with server code, which you are not doing when using NRF connect app; this has to be done manually

All above are only guessing, because there is not enough info to provide more accurate solution.

[Ashvajit.P]

1. your code is messed in many places, one i mentioned above, another is probably sending response on read request, which is not setting bit which tells its not whole value sent (due to MTU size)
2. i am guessing esp32 BLE client code is exchanging MTU with server code, which you are not doing when using NRF connect app; this has to be done manually

All above are only guessing, because there is not enough info to provide more accurate solution.

Even if I use GATT server example as it is, I am not able to increase response bytes greater than 22. Or I don't know how to do that properly.
I want to send 60-70 bytes of data, Is there any way to manage this payload size ?

[chegewara]

Screenshot_20220802-082708_nRF Connect.jpg (231.93 KiB) Viewed 2741 times