Add native USB CDC broker transport

src/usb_cdc_transport.h

@@ -0,0 +1,82 @@
+#pragma once
+
+#include <stdbool.h>
+#include <stdint.h>
+
+#include "esp_err.h"
+#include "session_broker.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/* USB CDC line-coding values are the numeric encodings defined by USB PSTN. */
+#define USB_CDC_TRANSPORT_STOP_BITS_1 0U
+#define USB_CDC_TRANSPORT_STOP_BITS_1_5 1U
+#define USB_CDC_TRANSPORT_STOP_BITS_2 2U
+
+#define USB_CDC_TRANSPORT_PARITY_NONE 0U
+#define USB_CDC_TRANSPORT_PARITY_ODD 1U
+#define USB_CDC_TRANSPORT_PARITY_EVEN 2U
+#define USB_CDC_TRANSPORT_PARITY_MARK 3U
+#define USB_CDC_TRANSPORT_PARITY_SPACE 4U
+
+typedef struct {
+    uint32_t baud_rate;
+    uint8_t stop_bits;
+    uint8_t parity;
+    uint8_t data_bits;
+} usb_cdc_transport_line_coding_t;
+
+typedef struct {
+    uint64_t host_rx_bytes;
+    uint64_t host_rx_stream_dropped_bytes;
+    uint64_t broker_accepted_bytes;
+    uint64_t broker_rejected_bytes;
+    uint64_t broker_to_usb_bytes;
+    /* Bytes admitted to TinyUSB's TX FIFO, not a host-delivery acknowledgement. */
+    uint64_t usb_tx_queued_bytes;
+    uint64_t usb_tx_dropped_bytes;
+    uint64_t connections;
+    uint64_t disconnections;
+    uint64_t writer_grants;
+    uint64_t writer_denials;
+    uint64_t writer_revocations;
+    uint64_t writer_events;
+    uint64_t service_start_failures;
+    uint64_t line_coding_applied;
+    uint64_t line_coding_rejected;
+    uint64_t line_coding_failed;
+    uint64_t callback_drops;
+    uint64_t control_drops;
+} usb_cdc_transport_counters_t;
+
+typedef struct {
+    bool initialized;
+    bool attached;
+    bool dtr;
+    bool rts;
+    session_broker_client_id_t broker_client_id;
+    bool writer;
+    usb_cdc_transport_line_coding_t line_coding;
+    usb_cdc_transport_counters_t counters;
+} usb_cdc_transport_snapshot_t;
+
+/*
+ * Installs the native ESP32-S3 USB-OTG device on GPIO19/20 as CDC-ACM 0.
+ * UART0 console/logging configuration is not changed.
+ */
+esp_err_t usb_cdc_transport_init(void);
+
+esp_err_t usb_cdc_transport_get_snapshot(usb_cdc_transport_snapshot_t *snapshot);
+
+/* Requests are asynchronous and execute in the transport task. */
+esp_err_t usb_cdc_transport_request_writer(void);
+esp_err_t usb_cdc_transport_release_writer(void);
+
+/* Clearing counters does not alter connection, ownership, or queued data. */
+esp_err_t usb_cdc_transport_clear_counters(void);
+
+#ifdef __cplusplus
+}
+#endif