diff --git a/main/usb_cdc.c b/main/usb_cdc.c
--- a/main/usb_cdc.c
+++ b/main/usb_cdc.c
@@ -12,12 +12,11 @@
 
 // Private variables
 static const char *TAG = "main";
+static uint8_t buf[CONFIG_TINYUSB_CDC_RX_BUFSIZE + 1];
 
 
-// ------------------------ USB CDC ----------------------------------------
-static uint8_t buf[CONFIG_TINYUSB_CDC_RX_BUFSIZE + 1];
-
-void tinyusb_cdc_rx_callback(int itf, cdcacm_event_t *event)
+// Callback for received data
+static void __cdc_rx_callback(int itf, cdcacm_event_t *event)
 {
     /* initialization */
     size_t rx_size = 0;
@@ -36,7 +35,9 @@ void tinyusb_cdc_rx_callback(int itf, cd
     tinyusb_cdcacm_write_flush(itf, 0);
 }
 
-void tinyusb_cdc_line_state_changed_callback(int itf, cdcacm_event_t *event)
+
+// Callback for line state changed
+void __cdc_line_state_changed_callback(int itf, cdcacm_event_t *event)
 {
     int dtr = event->line_state_changed_data.dtr;
     int rts = event->line_state_changed_data.rts;
@@ -44,6 +45,7 @@ void tinyusb_cdc_line_state_changed_call
 }
 
 
+// Initialize usb-cdc
 void usb_cdc_init(void)
 {
     ESP_LOGI(TAG, "USB initialization");
@@ -60,7 +62,7 @@ void usb_cdc_init(void)
         .usb_dev = TINYUSB_USBDEV_0,
         .cdc_port = TINYUSB_CDC_ACM_0,
         .rx_unread_buf_sz = 64,
-        .callback_rx = &tinyusb_cdc_rx_callback, // the first way to register a callback
+        .callback_rx = &__cdc_rx_callback, // the first way to register a callback
         .callback_rx_wanted_char = NULL,
         .callback_line_state_changed = NULL,
         .callback_line_coding_changed = NULL
@@ -71,7 +73,7 @@ void usb_cdc_init(void)
     ESP_ERROR_CHECK(tinyusb_cdcacm_register_callback(
                         TINYUSB_CDC_ACM_0,
                         CDC_EVENT_LINE_STATE_CHANGED,
-                        &tinyusb_cdc_line_state_changed_callback));
+                        &__cdc_line_state_changed_callback));
 
 #if (CONFIG_TINYUSB_CDC_COUNT > 1)
     acm_cfg.cdc_port = TINYUSB_CDC_ACM_1;