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docs/library/uos.rst: Improve block devices section, and ioctl ret vals.

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Peter Hinch 2020-01-12 09:20:36 +00:00 committed by Damien George
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commit 59746ac14a
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docs/library/uos.rst
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@ -218,11 +218,19 @@ represented by VFS classes.
Block devices
-------------
A block device is an object which implements the block protocol, which is a set
of methods described below by the :class:`AbstractBlockDev` class. A concrete
implementation of this class will usually allow access to the memory-like
functionality a piece of hardware (like flash memory). A block device can be
used by a particular filesystem driver to store the data for its filesystem.
A block device is an object which implements the block protocol. This enables a
device to support MicroPython filesystems. The physical hardware is represented
by a user defined class. The :class:`AbstractBlockDev` class is a template for
the design of such a class: MicroPython does not actually provide that class,
but an actual block device class must implement the methods described below.
A concrete implementation of this class will usually allow access to the
memory-like functionality of a piece of hardware (like flash memory). A block
device can be formatted to any supported filesystem and mounted using ``uos``
methods.
See :ref:`filesystem` for example implementations of block devices using the
two variants of the block protocol described below.
.. _block-device-interface:
@ -294,5 +302,12 @@ that the block device supports the extended interface.
(*arg* is unused)
- 6 -- erase a block, *arg* is the block number to erase
See :ref:`filesystem` for example implementations of block devices using both
protocols.
As a minimum ``ioctl(4, ...)`` must be intercepted; for littlefs
``ioctl(6, ...)`` must also be intercepted. The need for others is
hardware dependent.
Unless otherwise stated ``ioctl(op, arg)`` can return ``None``.
Consequently an implementation can ignore unused values of ``op``. Where
``op`` is intercepted, the return value for operations 4 and 5 are as
detailed above. Other operations should return 0 on success and non-zero
for failure, with the value returned being an ``OSError`` errno code.