docs/library: Add docs for pyb.Flash class.

docs/library/pyb.Flash.rst

@@ -0,0 +1,52 @@
+.. currentmodule:: pyb
+.. _pyb.Flash:
+
+class Flash -- access to built-in flash storage
+===============================================
+
+The Flash class allows direct access to the primary flash device on the pyboard.
+
+In most cases, to store persistent data on the device, you'll want to use a
+higher-level abstraction, for example the filesystem via Python's standard file
+API, but this interface is useful to :ref:`customise the filesystem
+configuration <filesystem>` or implement a low-level storage system for your
+application.
+
+Constructors
+------------
+
+.. class:: pyb.Flash()
+
+   Create and return a block device that represents the flash device presented
+   to the USB mass storage interface.
+
+   It includes a virtual partition table at the start, and the actual flash
+   starts at block ``0x100``.
+
+   This constructor is deprecated and will be removed in a future version of MicroPython.
+
+.. class:: pyb.Flash(\*, start=-1, len=-1)
+
+   Create and return a block device that accesses the flash at the specified offset. The length defaults to the remaining size of the device.
+
+   The *start* and *len* offsets are in bytes, and must be a multiple of the block size (typically 512 for internal flash).
+
+Methods
+-------
+
+.. method:: Flash.readblocks(block_num, buf)
+.. method:: Flash.readblocks(block_num, buf, offset)
+.. method:: Flash.writeblocks(block_num, buf)
+.. method:: Flash.writeblocks(block_num, buf, offset)
+.. method:: Flash.ioctl(cmd, arg)
+
+    These methods implement the simple and :ref:`extended
+    <block-device-interface>` block protocol defined by
+    :class:`uos.AbstractBlockDev`.
+
+Hardware Note
+-------------
+
+On boards with external spiflash (e.g. Pyboard D), the MicroPython firmware will
+be configured to use that as the primary flash storage. On all other boards, the
+internal flash inside the :term:`MCU` will be used.

docs/library/pyb.rst

@@ -309,6 +309,7 @@ Classes
    pyb.CAN.rst
    pyb.DAC.rst
    pyb.ExtInt.rst
+   pyb.Flash.rst
    pyb.I2C.rst
    pyb.LCD.rst
    pyb.LED.rst