Update docs for board_flash_mode

docs/platforms/espressif_extra.rst

@@ -26,10 +26,10 @@ Custom FLASH Frequency
 See :ref:`projectconf_board_f_flash` option from :ref:`projectconf`. Possible
 values:
 
-* 20000000L
-* 26000000L
-* 40000000L
-* 80000000L
+* ``20000000L``
+* ``26000000L``
+* ``40000000L``
+* ``80000000L``
 
 .. code-block:: ini
 
@@ -37,6 +37,27 @@ values:
     # set frequency to 80MHz
     board_f_flash = 80000000L
 
+Custom FLASH Mode
+-----------------
+
+Flash chip interface mode. This parameter is stored in the binary image
+header, along with the flash size and flash frequency. The ROM bootloader
+in the ESP chip uses the value of these parameters in order to know how to
+talk to the flash chip.
+
+See :ref:`projectconf_board_flash_mode` option from :ref:`projectconf`. Possible
+values:
+
+* ``qio``
+* ``qout``
+* ``dio``
+* ``dout``
+
+.. code-block:: ini
+
+    [env:myenv]
+    board_flash_mode = qio
+
 Custom Reset Method
 -------------------
 

docs/projectconf.rst

@@ -220,6 +220,14 @@ format of this option is ``C-like long integer`` value with ``L`` suffix. The
 This option isn't available for the all development platforms. The only
 :ref:`platform_espressif` supports it.
 
+.. _projectconf_board_flash_mode:
+
+``board_flash_mode``
+^^^^^^^^^^^^^^^^^^^^
+
+Flash chip interface mode. This option isn't available for the all development
+platforms. The only :ref:`platform_espressif` supports it.
+
 Building options
 ~~~~~~~~~~~~~~~~