feat(usb-otg): Finish the USB-OTG RX/TX support

Author: radimkarnis

CMakeLists.txt

@@ -23,7 +23,7 @@ set(srcs
     src/security.c
     src/uart.c
     src/usb_serial_jtag.c
-    src/usb_cdc.c
+    src/usb_otg.c
 )
 
 if(STUB_LOG_ENABLED IN_LIST STUB_COMPILE_DEFS)

include/esp-stub-lib/usb_cdc.h

@@ -0,0 +1,79 @@
+/*
+ * SPDX-FileCopyrightText: 2025 Espressif Systems (Shanghai) CO LTD
+ *
+ * SPDX-License-Identifier: Apache-2.0 OR MIT
+ */
+
+#pragma once
+
+#include <stdint.h>
+#include <stdbool.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif // __cplusplus
+
+/**
+ * @brief Check if USB-OTG is currently being used for communication
+ *
+ * This function checks if the ROM has initialized USB-OTG as the communication
+ * interface instead of UART.
+ *
+ * @return true if USB-OTG is active, false otherwise
+ */
+bool stub_lib_usb_otg_is_active(void);
+
+/**
+ * @brief Initialize USB-OTG for communication
+ *
+ * This function sets up USB-OTG interrupts and the RX callback function.
+ * It should be called after ROM initialization if USB-OTG is detected.
+ *
+ * @param intr_num Interrupt number
+ * @param rx_callback Callback function to be called when data is received
+ *                    The callback receives a single byte as parameter
+ */
+void stub_lib_usb_otg_rominit_intr_attach(int intr_num, void (*rx_callback)(uint8_t));
+
+/**
+ * @brief Transmit a single byte over USB-OTG
+ *
+ * @param c Byte to transmit
+ * @return 0 if successful, non-zero if error occurred
+ */
+uint8_t stub_lib_usb_otg_tx_one_char(uint8_t c);
+
+/**
+ * @brief Flush any buffered USB-OTG transmit data
+ */
+void stub_lib_usb_otg_tx_flush(void);
+
+/**
+ * @brief Enable or disable USB-OTG RX interrupts
+ *
+ * @param enable true to enable, false to disable
+ */
+void stub_lib_usb_otg_rx_async_enable(bool enable);
+
+/**
+ * @brief Check if USB-OTG reset was requested via RTS line
+ *
+ * This function checks if the host has requested a reset by toggling RTS.
+ * If reset is requested, the function returns true and should be followed
+ * by calling stub_lib_usb_otg_handle_reset().
+ *
+ * @return true if reset was requested, false otherwise
+ */
+bool stub_lib_usb_otg_is_reset_requested(void);
+
+/**
+ * @brief Handle USB-OTG reset request
+ *
+ * This function performs the necessary cleanup and prepares for reset.
+ * It should be called when stub_lib_usb_otg_is_reset_requested() returns true.
+ */
+void stub_lib_usb_otg_handle_reset(void);
+
+#ifdef __cplusplus
+}
+#endif // __cplusplus