ESP32-C3 BLE 5.0 분석 — GAP·GATT·Coded PHY

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// NimBLE: 연결 후 PHY 변경
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struct ble_gap_set_phy_args args = {
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    .tx_phys = BLE_GAP_LE_PHY_CODED_MASK,
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    .rx_phys = BLE_GAP_LE_PHY_CODED_MASK,
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    .phy_opts = BLE_HCI_LE_PHY_CODED_S8_PREF,
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};
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ble_gap_set_prefered_le_phy(conn_handle, args.tx_phys, args.rx_phys, args.phy_opts);

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// NimBLE advertising 시작
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static int gap_event_handler(struct ble_gap_event *event, void *arg)
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{
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    switch (event->type) {
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    case BLE_GAP_EVENT_CONNECT:
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        if (event->connect.status == 0) {
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            ESP_LOGI("ble", "connected handle=%d", event->connect.conn_handle);
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        }
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        break;
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    case BLE_GAP_EVENT_DISCONNECT:
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        ESP_LOGI("ble", "disconnected reason=%d", event->disconnect.reason);
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        ble_advertise_start();
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        break;
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    case BLE_GAP_EVENT_SUBSCRIBE:
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        ESP_LOGI("ble", "notify enabled=%d", event->subscribe.cur_notify);
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        break;
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    }
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    return 0;
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}
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void ble_advertise_start(void)
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{
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    struct ble_hs_adv_fields fields = {0};
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    fields.flags = BLE_HS_ADV_F_DISC_GEN | BLE_HS_ADV_F_BREDR_UNSUP;
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    fields.tx_pwr_lvl_is_present = 1;
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    fields.tx_pwr_lvl = BLE_HS_ADV_TX_PWR_LVL_AUTO;
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    fields.name = (uint8_t*)"ESP32-C3-Sensor";
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    fields.name_len = strlen("ESP32-C3-Sensor");
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    fields.name_is_complete = 1;
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    ble_gap_adv_set_fields(&fields);
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    struct ble_gap_adv_params adv_params = {
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        .conn_mode = BLE_GAP_CONN_MODE_UND,
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        .disc_mode = BLE_GAP_DISC_MODE_GEN,
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        .itvl_min = BLE_GAP_ADV_FAST_INTERVAL1_MIN, // 30 ms
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        .itvl_max = BLE_GAP_ADV_FAST_INTERVAL1_MAX, // 60 ms
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    };
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    ble_gap_adv_start(BLE_OWN_ADDR_PUBLIC, NULL, BLE_HS_FOREVER,
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                      &adv_params, gap_event_handler, NULL);
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}

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Battery Service (0x180F)
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├── Battery Level Characteristic (0x2A19)
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│   ├── value (uint8, 0~100)
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│   ├── property: READ | NOTIFY
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│   └── descriptor: CCCD (0x2902) — notify 활성화 비트
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└── (다른 characteristic은 옵션)

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static uint8_t battery_level = 87;
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static int battery_level_access(uint16_t conn_handle, uint16_t attr_handle,
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                                 struct ble_gatt_access_ctxt *ctxt, void *arg)
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{
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    if (ctxt->op == BLE_GATT_ACCESS_OP_READ_CHR) {
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        os_mbuf_append(ctxt->om, &battery_level, sizeof(battery_level));
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        return 0;
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    }
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    return BLE_ATT_ERR_UNLIKELY;
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}
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static const struct ble_gatt_svc_def gatt_svcs[] = {
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    {
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        .type = BLE_GATT_SVC_TYPE_PRIMARY,
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        .uuid = BLE_UUID16_DECLARE(0x180F),  // Battery Service
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        .characteristics = (struct ble_gatt_chr_def[]) {
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            {
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                .uuid = BLE_UUID16_DECLARE(0x2A19),
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                .access_cb = battery_level_access,
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                .flags = BLE_GATT_CHR_F_READ | BLE_GATT_CHR_F_NOTIFY,
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            },
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            { 0 } // terminator
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        },
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    },
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    { 0 } // terminator
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};
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void gatt_init(void)
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{
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    ble_svc_gap_init();
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    ble_svc_gatt_init();
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    ble_gatts_count_cfg(gatt_svcs);
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    ble_gatts_add_svcs(gatt_svcs);
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}

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// 1초마다 battery level notify
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void battery_notify_task(void *param)
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{
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    while (1) {
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        if (current_conn_handle != BLE_HS_CONN_HANDLE_NONE) {
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            struct os_mbuf *om = ble_hs_mbuf_from_flat(&battery_level, 1);
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            ble_gatts_notify_custom(current_conn_handle,
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                                     battery_level_attr_handle, om);
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        }
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        vTaskDelay(pdMS_TO_TICKS(1000));
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    }
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}

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ble_hs_cfg.sm_io_cap = BLE_SM_IO_CAP_NO_IO;          // Just Works
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// ble_hs_cfg.sm_io_cap = BLE_SM_IO_CAP_DISP_ONLY;   // Passkey display
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// ble_hs_cfg.sm_io_cap = BLE_SM_IO_CAP_KEYBOARD_ONLY;
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ble_hs_cfg.sm_bonding = 1;       // bond 저장
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ble_hs_cfg.sm_mitm = 1;          // MITM 방어 요구
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ble_hs_cfg.sm_sc = 1;            // LE Secure Connections (ECDH P-256)

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시간 ──────────────────────────────────────►
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WiFi:  ███   ██     ████    ██   ███
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BLE:      ██    ███     ██     ██    ██
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       양쪽 모두 약 50%씩 시간 점유

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// menuconfig: Component config → Bluetooth → Bluetooth controller
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// CONFIG_BT_CTRL_COEX_PHY_CODED_TX_RX_TIME_LIMIT (BLE Coded PHY 우선)
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// Component config → Wi-Fi → CONFIG_ESP_COEX_SW_COEXIST_ENABLE