docs(advanced-topics): Fixed strapping pin for Automatic Bootloader s…

…ection

docs/en/advanced-topics/boot-mode-selection.rst

@@ -125,7 +125,7 @@ Automatic Bootloader
 
 As an example of auto-reset curcuitry implementation, check the `schematic <https://dl.espressif.com/dl/schematics/esp32_devkitc_v4-sch-20180607a.pdf>`_ of the ESP32 DevKitC development board:
 
--  The **Micro USB 5V & USB-UART** section shows the ``DTR`` and ``RTS`` control lines of the USB to serial converter chip connected to ``GPIO0`` and ``EN`` pins of the ESP module.
+-  The **Micro USB 5V & USB-UART** section shows the ``DTR`` and ``RTS`` control lines of the USB to serial converter chip connected to ``{IDF_TARGET_STRAP_BOOT_GPIO}`` and ``EN`` pins of the ESP module.
 -  Some OS and/or drivers may activate ``RTS`` and or ``DTR`` automatically when opening the serial port (true only for some serial terminal programs, not ``esptool.py``), pulling them low together and holding the ESP in reset. If ``RTS`` is wired directly to ``EN`` then RTS/CTS "hardware flow control" needs to be disabled in the serial program to avoid this.
    An additional circuitry is implemented in order to avoid this problem - if both ``RTS`` and ``DTR`` are asserted together, this doesn't reset the chip. The schematic shows this specific circuit with two transistors and its truth table.
 -  If this circuitry is implemented (all Espressif boards have it), adding a capacitor between the ``EN`` pin and ``GND`` (in the 1uF-10uF range) is necessary for the reset circuitry to work reliably. This is shown in the **ESP32 Module** section of the schematic.

test/test_esptool.py

@@ -1049,6 +1049,12 @@ class TestLoadRAM(EsptoolTestCase):
 
     def verify_output(self, expected_out: List[bytes]):
         """Verify that at least one element of expected_out is in serial output"""
+        # Setting rtscts to true enables hardware flow control.
+        # This removes unwanted RTS logic level changes for some machines
+        # (and, therefore, chip resets)
+        # when the port is opened by the following function.
+        # As a result, the app loaded to RAM has a chance to run and send
+        # "Hello world" data without unwanted chip reset.
         with serial.serial_for_url(arg_port, arg_baud, rtscts=True) as p:
             p.timeout = 5
             output = p.read(100)