2 COM ports in Windows when Bluetooth SPP connects

kbaud1
Posts: 47
Joined: Wed Jan 17, 2018 11:55 pm

2 COM ports in Windows when Bluetooth SPP connects

Postby kbaud1 » Tue Jul 16, 2019 3:48 pm

When I connect the ESP32 to my PC, I see 2 com ports in windows. I searched online for an answer. Found some examples but they showed two com ports as well. One of the ports (which one changes randomly) does not work. You have to try both. The 2 ports show up in windows device manager and at the command prompt ("wmic path Win32_SerialPort").

This appears to effect SPP ports created either using the IDF or Arduino.

The source I am using (IDF):

Code: Select all

#include <stdint.h>
#include <string.h>
#include <stdbool.h>
#include <stdio.h>
#include "nvs.h"
#include "nvs_flash.h"
#include "freertos/FreeRTOS.h"
#include "freertos/task.h"
#include "esp_log.h"
#include "esp_bt.h"
#include "esp_bt_main.h"
#include "esp_gap_bt_api.h"
#include "esp_bt_device.h"
#include "esp_spp_api.h"

#define SPP_TAG "SPP_ACCEPTOR_DEMO"
#define SPP_SERVER_NAME "SPP_SERVER"
#define EXAMPLE_DEVICE_NAME "ESP_SPP_ACCEPTOR"

static const esp_spp_mode_t esp_spp_mode = ESP_SPP_MODE_CB;
static const esp_spp_sec_t sec_mask = ESP_SPP_SEC_NONE;
static const esp_spp_role_t role_slave = ESP_SPP_ROLE_SLAVE;

static void esp_spp_cb(esp_spp_cb_event_t event, esp_spp_cb_param_t *param)
{
    switch (event) {
    case ESP_SPP_INIT_EVT:
        ESP_LOGI(SPP_TAG, "ESP_SPP_INIT_EVT");
        esp_bt_dev_set_device_name(EXAMPLE_DEVICE_NAME);
        esp_bt_gap_set_scan_mode(ESP_BT_SCAN_MODE_CONNECTABLE_DISCOVERABLE);
        esp_spp_start_srv(sec_mask,role_slave, 0, SPP_SERVER_NAME);
        break;
    case ESP_SPP_DISCOVERY_COMP_EVT:
        ESP_LOGI(SPP_TAG, "ESP_SPP_DISCOVERY_COMP_EVT");
        break;
    case ESP_SPP_OPEN_EVT:
        ESP_LOGI(SPP_TAG, "ESP_SPP_OPEN_EVT");
        break;
    case ESP_SPP_CLOSE_EVT:
        ESP_LOGI(SPP_TAG, "ESP_SPP_CLOSE_EVT");
        break;
    case ESP_SPP_START_EVT:
        ESP_LOGI(SPP_TAG, "ESP_SPP_START_EVT");
        break;
    case ESP_SPP_CL_INIT_EVT:
        ESP_LOGI(SPP_TAG, "ESP_SPP_CL_INIT_EVT");
        break;
    case ESP_SPP_DATA_IND_EVT:
    	ets_delay_us (50);
        ESP_LOGI(SPP_TAG, "ESP_SPP_DATA_IND_EVT len=%d handle=%d",
                 param->data_ind.len, param->data_ind.handle);
        if (param->data_ind.len < 1023) {
            esp_spp_write(param->write.handle, (size_t)param->data_ind.len, (uint8_t *)param->data_ind.data);
        }
        else {
            esp_log_buffer_hex("",param->data_ind.data,param->data_ind.len);
        }
        break;
    case ESP_SPP_CONG_EVT:
        ESP_LOGI(SPP_TAG, "ESP_SPP_CONG_EVT");
        break;
    case ESP_SPP_WRITE_EVT:
        ESP_LOGI(SPP_TAG, "ESP_SPP_WRITE_EVT");
        break;
    case ESP_SPP_SRV_OPEN_EVT:
        ESP_LOGI(SPP_TAG, "ESP_SPP_SRV_OPEN_EVT");
        break;
    default:
        break;
    }
}

void app_main()
{
    esp_err_t ret = nvs_flash_init();
    if (ret == ESP_ERR_NVS_NO_FREE_PAGES) {
        ESP_ERROR_CHECK(nvs_flash_erase());
        ret = nvs_flash_init();
    }
    ESP_ERROR_CHECK( ret );


    esp_bt_controller_config_t bt_cfg = BT_CONTROLLER_INIT_CONFIG_DEFAULT();
    if (esp_bt_controller_init(&bt_cfg) != ESP_OK) {
        ESP_LOGE(SPP_TAG, "%s initialize controller failed\n", __func__);
        return;
    }

    if (esp_bt_controller_enable(ESP_BT_MODE_CLASSIC_BT) != ESP_OK) {
        ESP_LOGE(SPP_TAG, "%s enable controller failed\n", __func__);
        return;
    }

    if (esp_bluedroid_init() != ESP_OK) {
        ESP_LOGE(SPP_TAG, "%s initialize bluedroid failed\n", __func__);
        return;
    }

    if (esp_bluedroid_enable() != ESP_OK) {
        ESP_LOGE(SPP_TAG, "%s enable bluedroid failed\n", __func__);
        return;
    }

    if (esp_spp_register_callback(esp_spp_cb) != ESP_OK) {
        ESP_LOGE(SPP_TAG, "%s spp register failed\n", __func__);
        return;
    }

    if (esp_spp_init(esp_spp_mode) != ESP_OK) {
        ESP_LOGE(SPP_TAG, "%s spp init failed\n", __func__);
        return;
    }
}
An example I found online of what this looks like:

Image
Last edited by kbaud1 on Tue Jul 16, 2019 4:44 pm, edited 1 time in total.

kbaud1
Posts: 47
Joined: Wed Jan 17, 2018 11:55 pm

Re: 2 COM ports in Windows when Bluetooth SPP connects

Postby kbaud1 » Tue Jul 16, 2019 4:39 pm

I did notice that under "Bluetooth settings" in windows, one port is listed at incoming and one is listed as outgoing. but when I connect to the correct port (whichever one it is at that time), I can send and receive. how to only get one port? the "outgoing" port seems to be the one that works. but this changes and not sure how a program would automatically find this.

Apparently, this is a common "feature" of bluetooth SPP devices? Here is an example I found online:

Image


kbaud1
Posts: 47
Joined: Wed Jan 17, 2018 11:55 pm

Re: 2 COM ports in Windows when Bluetooth SPP connects

Postby kbaud1 » Thu Jul 18, 2019 1:59 pm

Thank you for the link. So it appears to be normal. I will need to figure out how the application will know which port to use since it varies from connection to connection. I could test both, might be able to find a register value, etc.

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