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| -rw-r--r-- | docs/library/uos.rst | 29 |
1 files changed, 22 insertions, 7 deletions
diff --git a/docs/library/uos.rst b/docs/library/uos.rst index cbc1f3e915..c49b13a5f5 100644 --- a/docs/library/uos.rst +++ b/docs/library/uos.rst @@ -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. |