Fix CDC fallback logic/path, add ESP32 CDC examples

.github/workflows/build_arduinoide.yaml

@@ -25,6 +25,8 @@ jobs:
               source-url: https://raw.githubusercontent.com/espressif/arduino-esp32/gh-pages/package_esp32_index.json
           sketch-paths: |
             - examples/loopback
+            - examples/native_host
+            - examples/native_peripheral
           libraries: |
             - name: USBHostSerial
               source-path: ./

.github/workflows/build_platformio.yaml

@@ -9,9 +9,10 @@ jobs:
     container: ghcr.io/bertmelis/pio-test-container
     strategy:
       matrix:
-        example: [
-          examples/loopback/loopback.ino
-        ]
+        example:
+          - examples/loopback/loopback.ino
+          - examples/native_host/native_host.ino
+          - examples/native_peripheral/native_peripheral.ino
     steps:
       - uses: actions/checkout@v4
       - uses: actions/cache@v4

examples/native_host/native_host.ino

@@ -0,0 +1,48 @@
+/**
+ * @file native_host.ino
+ * @brief Example sketch for USBHostSerial library demonstrating native USB host functionality.
+ * @date 4/1/26
+ * @author Aldem Pido
+ * 
+ * Tested with 2ESP32 S3 Wroom 2 Boards with UART and USB ports.
+ * 
+ * Host Board
+ * USB -> Peripheral USB
+ * UART -> Computer Serial Monitor
+ * 
+ * Peripheral Board
+ * USB -> Peripheral USB
+ * UART -> Computer Serial Monitor
+ */
+#define USBHOSTSERIAL_BUFFERSIZE 512
+#include <Arduino.h>
+#include <USBHostSerial.h>
+
+USBHostSerial hostSerial;
+
+// Logger function for USBHostSerial
+void usbHostLogger(const char* msg) {
+  Serial.print("[USBHostSerial] ");
+  Serial.println(msg);
+}
+
+void setup() {
+  Serial.begin(115200);
+  delay(1000);
+
+  hostSerial.begin(115200, 0, 0, 8); // baudrate, stopbits, parity, databits
+  hostSerial.setLogger(usbHostLogger);  // Enable logging
+}
+
+void loop() {
+  // Host to Serial
+  if (hostSerial.available()) {
+    Serial.write(hostSerial.read());
+    Serial.flush();
+  }
+
+  // Serial to Host
+  if (Serial.available()) {
+    hostSerial.write(Serial.read());
+  }
+}

examples/native_peripheral/native_peripheral.ino

@@ -0,0 +1,32 @@
+/**
+ * @file native_peripheral.ino
+ * @brief Flushes data between Native USB Serial and UART Serial
+ * @date 4/1/26
+ * @author Aldem Pido
+ */
+
+#include "USB.h"
+#include "USBCDC.h"
+
+USBCDC USBSerial;
+
+void setup() {
+  Serial.begin(115200);
+  USBSerial.begin();
+  USB.begin();
+  delay(1000);
+}
+
+void loop() {
+  // USB to Serial
+  if (USBSerial.available()) {
+    Serial.write(USBSerial.read());
+    Serial.flush();
+  }
+
+  // Serial to USB
+  if (Serial.available()) {
+    USBSerial.write(Serial.read());
+    USBSerial.flush();
+  }
+}

src/USBHostSerial.cpp

@@ -177,6 +177,7 @@ bool USBHostSerial::_handle_rx(const uint8_t *data, size_t data_len, void *arg)
 
 void USBHostSerial::_handle_event(const cdc_acm_host_dev_event_data_t *event, void *user_ctx) {
   if (event->type == CDC_ACM_HOST_DEVICE_DISCONNECTED) {
+    static_cast<USBHostSerial*>(user_ctx)->_log("USB device disconnected event");
     xSemaphoreGive(static_cast<USBHostSerial*>(user_ctx)->_device_disconnected_sem);
   }
 }
@@ -207,9 +208,11 @@ void USBHostSerial::_USBHostSerial_task(void *arg) {
     cdc_acm_dev_hdl_t cdc_dev = NULL;
     auto vcp = std::unique_ptr<CdcAcmDevice>(VCP::open(&dev_config));
     if (vcp == nullptr) {
+      thisInstance->_log("USB VCP open returned null, falling back to CDC");
       // try to fallback to CDC
       err = cdc_acm_host_open(thisInstance->_vid, thisInstance->_pid, 0, &dev_config, &cdc_dev);
       if (err != ESP_OK) {
+        vTaskDelay(pdMS_TO_TICKS(500));
         continue;
       }
       thisInstance->_fallback = true;
@@ -219,21 +222,58 @@ void USBHostSerial::_USBHostSerial_task(void *arg) {
       thisInstance->_log("USB VCP device opened");
     }
 
-    // mark connected
-    xSemaphoreTake(thisInstance->_device_disconnected_sem, portMAX_DELAY);
+    // Clear any stale disconnect token from a previous cycle.
+    while (xSemaphoreTake(thisInstance->_device_disconnected_sem, 0) == pdTRUE) {
+    }
 
-    // set line coding
+    // set line coding and control line states
     err = ESP_OK;
     if (thisInstance->_fallback) {
-      err = cdc_acm_host_line_coding_get(cdc_dev, &(thisInstance->_line_coding));
+      err = cdc_acm_host_line_coding_set(cdc_dev, &(thisInstance->_line_coding));
+      if (err != ESP_OK) {
+        thisInstance->_log("USB line coding set error");
+        if (cdc_dev != NULL) {
+          cdc_acm_host_close(cdc_dev);
+          cdc_dev = NULL;
+        }
+        vTaskDelay(pdMS_TO_TICKS(500));
+        continue;
+      }
+      thisInstance->_log("USB line coding set");
+
+      err = cdc_acm_host_set_control_line_state(cdc_dev, true, true);
+      if (err == ESP_ERR_NOT_SUPPORTED) {
+        thisInstance->_log("USB control line state not supported");
+      } else if (err != ESP_OK) {
+        thisInstance->_log("USB control line state set error");
+        if (cdc_dev != NULL) {
+          cdc_acm_host_close(cdc_dev);
+          cdc_dev = NULL;
+        }
+        vTaskDelay(pdMS_TO_TICKS(500));
+        continue;
+      } else {
+        thisInstance->_log("USB control line state set");
+      }
     } else {
       err = vcp->line_coding_set(&(thisInstance->_line_coding));
-    }
-    if (err == ESP_OK) {
+      if (err != ESP_OK) {
+        thisInstance->_log("USB line coding set error");
+        vTaskDelay(pdMS_TO_TICKS(500));
+        continue;
+      }
       thisInstance->_log("USB line coding set");
-    } else {
-      thisInstance->_log("USB line coding error");
-      continue;
+
+      err = vcp->set_control_line_state(true, true);
+      if (err == ESP_ERR_NOT_SUPPORTED) {
+        thisInstance->_log("USB control line state not supported");
+      } else if (err != ESP_OK) {
+        thisInstance->_log("USB control line state set error");
+        vTaskDelay(pdMS_TO_TICKS(500));
+        continue;
+      } else {
+        thisInstance->_log("USB control line state set");
+      }
     }
 
     // all set, enter loop to start sending
@@ -255,11 +295,23 @@ void USBHostSerial::_USBHostSerial_task(void *arg) {
         if (err == ESP_OK) {
           vRingbufferReturnItem(thisInstance->_tx_buf_handle, data);
         } else {
+          vRingbufferReturnItem(thisInstance->_tx_buf_handle, data);
           thisInstance->_log("Error writing to USB");
+          // Device likely reset/disconnected; break to cleanup/reopen path.
+          if (err == ESP_ERR_INVALID_STATE || err == ESP_ERR_INVALID_RESPONSE || err == ESP_FAIL) {
+            break;
+          }
         }
       }
       taskYIELD();
     }
+
+    // Ensure CDC handles are released before attempting to reopen.
+    if (thisInstance->_fallback && cdc_dev != NULL) {
+      cdc_acm_host_close(cdc_dev);
+      cdc_dev = NULL;
+    }
+    vTaskDelay(pdMS_TO_TICKS(500));
   }
 }