🛠 Dompter le double USB : Serial/JTAG et OTG de front

Objectives

Leverage the unique feature of the ESP32-S3: two simultaneous USB personalities. On one side, the USB-Serial/JTAG peripheral (serial console + hardware debugging without an external bridge); on the other, the USB-OTG controller (HID/MSC/CDC device or host). On boards that wire both controllers to two distinct connectors (some DevKitC-1, ESP32-S3-Box), you can flash and debug via one port while emulating a keyboard on the other. You will configure the Hardware CDC+JTAG mode, launch a debug session, and understand pin routing.

Hardware

• 1 ESP32-S3 board exposing both ports (or a UART adapter on GPIO43/44 as a fallback)
• 2 USB cables
• Arduino IDE (esp32 core >= 2.0.14) or ESP-IDF v5.x with OpenOCD for JTAG

Full Code

// Mode "Hardware CDC and JTAG" : console + debug sur le port Serial/JTAG,
// le port OTG (GPIO19/20) reste libre pour un peripherique TinyUSB.
// Outils Arduino : USB CDC On Boot = Enabled,
//                  USB Mode = "Hardware CDC and JTAG"
#include "Arduino.h"

// Point d'arret logiciel : si un debogueur JTAG est attache, il s'y connecte ;
// sinon la boucle courte evite toute surprise côté watchdog.
volatile int drapeau_debug = 0;

void setup {
  Serial.begin(115200);            // passe par USB-Serial/JTAG (pas GPIO43/44)
  Serial.println("Boot sur USB-Serial/JTAG");
}

void loop {
  static uint32_t n = 0;
  if (drapeau_debug) {             // breakpoint logiciel : pause pour GDB
    while (drapeau_debug) { asm volatile("nop"); delay(1); }
  }
  if (++n % 50 == 0) Serial.printf("tick %u, heap %u\n", n, ESP.getFreeHeap);
  delay(20);
}

On the ESP-IDF side, the JTAG console is enabled via idf.py menuconfig → Component config → ESP System → “Channel for console output” → “USB Serial/JTAG”, and debugging via idf.py openocd followed by idf.py gdb (or the VS Code launch configuration “OpenOCD GDB Server”).

Expected Verification

Connected to the Serial/JTAG port, the board presents a serial port without any bridge chip; the console works at USB link speed. In debug mode (ESP-IDF), GDB attaches via the same cable: breakpoints, stepping, and memory reading without external JTAG. On a board with two connectors, the second port remains available for a TinyUSB device: the two worlds truly coexist.

Common Errors

• Confusing the two controllers: “USB CDC On Boot” drives the hardware Serial/JTAG (internal pins), whereas TinyUSB requires GPIO19/20; enabling both simultaneously on the same pins results in a phantom or non-existent port.
• Lost console after switching to TinyUSB: the Serial/JTAG port is no longer initialized; reflash while holding BOOT + RESET (ROM mode) or connect a serial adapter to GPIO43 (RX) / GPIO44 (TX) / GND.
• Watch out for resets: the Serial/JTAG peripheral may trigger a DTR/RTS reset when opening the port; disable DTR/RTS in the terminal if your script gets reset.
• Console speed: with Serial/JTAG, the actual throughput depends on the host, not the configured baud rate; do not look for a “2000000” UART setting.
• GDB failing to attach: verify that the cable is connected to the correct connector (the Serial/JTAG one, not the OTG) and that no program is configuring GPIO19/20 as outputs.