Reading Data

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Within the switch statement defined in esp_profile_a_event_handler() , we have a case which responds to the Gatts event ESP_GATTS_READ_EVT . This is the case wherein the Central Device has requested to read some data ..

Response Structure

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We begin by logging when the ESP_GATTS_READ_EVT is received .

    case ESP_GATTS_READ_EVT: {
        ESP_LOGI(GATTS_TAG, "Characteristic read, conn_id %d, trans_id %" PRIu32 ", handle %d", param->read.conn_id, param->read.trans_id, param->read.handle);

Next we prepare our response to the Central Device . Here we utilize an esp_gatt_rsp_t which holds the GATT attribute value, including its data, handle, and metadata.

        esp_gatt_rsp_t rsp;
        memset(&rsp, 0, sizeof(esp_gatt_rsp_t));
        rsp.attr_value.handle = param->read.handle;
        rsp.attr_value.len = 4;
        rsp.attr_value.value[0] = 0xde;
        rsp.attr_value.value[1] = 0xed;
        rsp.attr_value.value[2] = 0xbe;
        rsp.attr_value.value[3] = 0xef;
        esp_ble_gatts_send_response(gatts_if, param->read.conn_id, param->read.trans_id,
                                    ESP_GATT_OK, &rsp);
        break;
    }

Response Structure

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esp_gatt_rsp_t rsp

• Purpose : represents the response type for a GATT remote read request.
• Members ..
  • esp_gatt_value_t attr_value : he GATT attribute value, including its data, handle, and metadata.
  • uint16_t : Only the handle of the GATT attribute, when that's the only required information.

esp_gatt_value_t attr_value

• Purpose : Represents a GATT attribute's value.
• Members : We only concern ourselves with the .value & .len to set data within the array and the current length of the data in the value array respectively . for more see the entire Struct Implementaiton