156 lines
8.4 KiB
ReStructuredText
156 lines
8.4 KiB
ReStructuredText
Glossary
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========
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.. glossary::
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baremetal
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A system without a (full-fledged) OS, for example an
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:term:`MCU`-based system. When running on a baremetal system,
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MicroPython effectively becomes its user-facing OS with a command
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interpreter (REPL).
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board
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A PCB board. Oftentimes, the term is used to denote a particular
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model of an :term:`MCU` system. Sometimes, it is used to actually
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refer to :term:`MicroPython port` to a particular board (and then
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may also refer to "boardless" ports like
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:term:`Unix port <MicroPython Unix port>`).
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callee-owned tuple
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A tuple returned by some builtin function/method, containing data
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which is valid for a limited time, usually until next call to the
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same function (or a group of related functions). After next call,
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data in the tuple may be changed. This leads to the following
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restriction on the usage of callee-owned tuples - references to
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them cannot be stored. The only valid operation is extracting
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values from them (including making a copy). Callee-owned tuples
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is a MicroPython-specific construct (not available in the general
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Python language), introduced for memory allocation optimization.
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The idea is that callee-owned tuple is allocated once and stored
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on the callee side. Subsequent calls don't require allocation,
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allowing to return multiple values when allocation is not possible
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(e.g. in interrupt context) or not desirable (because allocation
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inherently leads to memory fragmentation). Note that callee-owned
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tuples are effectively mutable tuples, making an exception to
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Python's rule that tuples are immutable. (It may be interesting
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why tuples were used for such a purpose then, instead of mutable
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lists - the reason for that is that lists are mutable from user
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application side too, so a user could do things to a callee-owned
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list which the callee doesn't expect and could lead to problems;
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a tuple is protected from this.)
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CPython
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CPython is the reference implementation of Python programming
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language, and the most well-known one, which most of the people
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run. It is however one of many implementations (among which
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Jython, IronPython, PyPy, and many more, including MicroPython).
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As there is no formal specification of the Python language, only
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CPython documentation, it is not always easy to draw a line
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between Python the language and CPython its particular
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implementation. This however leaves more freedom for other
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implementations. For example, MicroPython does a lot of things
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differently than CPython, while still aspiring to be a Python
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language implementation.
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GPIO
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General-purpose input/output. The simplest means to control
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electrical signals. With GPIO, user can configure hardware
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signal pin to be either input or output, and set or get
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its digital signal value (logical "0" or "1"). MicroPython
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abstracts GPIO access using :class:`machine.Pin` and :class:`machine.Signal`
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classes.
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GPIO port
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A group of :term:`GPIO` pins, usually based on hardware
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properties of these pins (e.g. controllable by the same
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register).
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interned string
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A string referenced by its (unique) identity rather than its
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address. Interned strings are thus can be quickly compared just
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by their identifiers, instead of comparing by content. The
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drawbacks of interned strings are that interning operation takes
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time (proportional to the number of existing interned strings,
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i.e. becoming slower and slower over time) and that the space
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used for interned strings is not reclaimable. String interning
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is done automatically by MicroPython compiler and runtimer when
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it's either required by the implementation (e.g. function keyword
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arguments are represented by interned string id's) or deemed
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beneficial (e.g. for short enough strings, which have a chance
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to be repeated, and thus interning them would save memory on
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copies). Most of string and I/O operations don't produce interned
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strings due to drawbacks described above.
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MCU
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Microcontroller. Microcontrollers usually have much less resources
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than a full-fledged computing system, but smaller, cheaper and
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require much less power. MicroPython is designed to be small and
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optimized enough to run on an average modern microcontroller.
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micropython-lib
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MicroPython is (usually) distributed as a single executable/binary
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file with just few builtin modules. There is no extensive standard
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library comparable with :term:`CPython`. Instead, there is a related, but
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separate project
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`micropython-lib <https://github.com/micropython/micropython-lib>`_
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which provides implementations for many modules from CPython's
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standard library. However, large subset of these modules require
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POSIX-like environment (Linux, FreeBSD, MacOS, etc.; Windows may be
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partially supported), and thus would work or make sense only with
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`MicroPython Unix port`. Some subset of modules is however usable
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for `baremetal` ports too.
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Unlike monolithic :term:`CPython` stdlib, micropython-lib modules
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are intended to be installed individually - either using manual
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copying or using :term:`upip`.
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MicroPython port
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MicroPython supports different :term:`boards <board>`, RTOSes,
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and OSes, and can be relatively easily adapted to new systems.
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MicroPython with support for a particular system is called a
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"port" to that system. Different ports may have widely different
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functionality. This documentation is intended to be a reference
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of the generic APIs available across different ports ("MicroPython
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core"). Note that some ports may still omit some APIs described
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here (e.g. due to resource constraints). Any such differences,
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and port-specific extensions beyond MicroPython core functionality,
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would be described in the separate port-specific documentation.
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MicroPython Unix port
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Unix port is one of the major :term:`MicroPython ports <MicroPython port>`.
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It is intended to run on POSIX-compatible operating systems, like
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Linux, MacOS, FreeBSD, Solaris, etc. It also serves as the basis
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of Windows port. The importance of Unix port lies in the fact
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that while there are many different :term:`boards <board>`, so
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two random users unlikely have the same board, almost all modern
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OSes have some level of POSIX compatibility, so Unix port serves
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as a kind of "common ground" to which any user can have access.
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So, Unix port is used for initial prototyping, different kinds
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of testing, development of machine-independent features, etc.
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All users of MicroPython, even those which are interested only
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in running MicroPython on :term:`MCU` systems, are recommended
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to be familiar with Unix (or Windows) port, as it is important
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productivity helper and a part of normal MicroPython workflow.
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port
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Either :term:`MicroPython port` or :term:`GPIO port`. If not clear
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from context, it's recommended to use full specification like one
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of the above.
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stream
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Also known as a "file-like object". An object which provides sequential
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read-write access to the underlying data. A stream object implements
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a corresponding interface, which consists of methods like ``read()``,
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``write()``, ``readinto()``, ``seek()``, ``flush()``, ``close()``, etc.
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A stream is an important concept in MicroPython, many I/O objects
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implement the stream interface, and thus can be used consistently and
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interchangeably in different contexts. For more information on
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streams in MicroPython, see `uio` module.
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upip
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(Literally, "micro pip"). A package manage for MicroPython, inspired
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by :term:`CPython`'s pip, but much smaller and with reduced functionality.
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upip runs both on :term:`Unix port <MicroPython Unix port>` and on
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:term:`baremetal` ports (those which offer filesystem and networking
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support).
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