:mod:`micropython` --- access and control MicroPython internals =============================================================== .. module:: micropython :synopsis: access and control MicroPython internals Functions --------- .. function:: const(expr: int) -> int Used to declare that the expression is a constant so that the compiler can optimise it. The use of this function should be as follows:: from micropython import const CONST_X = const(123) CONST_Y = const(2 * CONST_X + 1) Constants declared this way are still accessible as global variables from outside the module they are declared in. On the other hand, if a constant begins with an underscore then it is hidden, it is not available as a global variable, and does not take up any memory during execution. This `const` function is recognised directly by the MicroPython parser and is provided as part of the :mod:`micropython` module mainly so that scripts can be written which run under both CPython and MicroPython, by following the above pattern. .. function:: opt_level(level: Optional[int] = None) -> Optional[int] If *level* is given then this function sets the optimisation level for subsequent compilation of scripts, and returns ``None``. Otherwise it returns the current optimisation level. The optimisation level controls the following compilation features: - Assertions: at level 0 assertion statements are enabled and compiled into the bytecode; at levels 1 and higher assertions are not compiled. - Built-in ``__debug__`` variable: at level 0 this variable expands to ``True``; at levels 1 and higher it expands to ``False``. - Source-code line numbers: at levels 0, 1 and 2 source-code line number are stored along with the bytecode so that exceptions can report the line number they occurred at; at levels 3 and higher line numbers are not stored. The default optimisation level is usually level 0. .. function:: alloc_emergency_exception_buf(size: int) -> None Allocate *size* bytes of RAM for the emergency exception buffer (a good size is around 100 bytes). The buffer is used to create exceptions in cases when normal RAM allocation would fail (eg within an interrupt handler) and therefore give useful traceback information in these situations. A good way to use this function is to put it at the start of your main script (eg ``boot.py`` or ``main.py``) and then the emergency exception buffer will be active for all the code following it. .. function:: mem_info(verbose: Optional[Any] = None) -> None Print information about currently used memory. If the *verbose* argument is given then extra information is printed. The information that is printed is implementation dependent, but currently includes the amount of stack and heap used. In verbose mode it prints out the entire heap indicating which blocks are used and which are free. .. function:: qstr_info(verbose: Optional[Any] = None) -> None Print information about currently interned strings. If the *verbose* argument is given then extra information is printed. The information that is printed is implementation dependent, but currently includes the number of interned strings and the amount of RAM they use. In verbose mode it prints out the names of all RAM-interned strings. .. function:: stack_use() -> int Return an integer representing the current amount of stack that is being used. The absolute value of this is not particularly useful, rather it should be used to compute differences in stack usage at different points. .. function:: heap_lock() -> None Lock the heap. While locked, no memory allocation can occur and a `MemoryError` will be raised if any heap allocation is attempted. Locks nest: calling `heap_lock()` multiple times increases the lock depth. The heap remains locked until `heap_unlock()` has been called the same number of times. If the REPL becomes active with the heap locked then it will be forcefully unlocked. .. function:: heap_unlock() -> int Decrement the heap lock depth by one and return the new depth as a non-negative integer. A return value of ``0`` means the heap is no longer locked and allocations are once again permitted. .. function:: heap_locked() -> int Return the current heap lock depth as a non-negative integer; ``0`` means the heap is not locked. Note: this function is not available on the OpenMV Cam. .. function:: kbd_intr(chr: int) -> None Set the character that will raise a `KeyboardInterrupt` exception. By default this is set to 3 during script execution, corresponding to Ctrl-C. Passing -1 to this function will disable capture of Ctrl-C, and passing 3 will restore it. This function can be used to prevent the capturing of Ctrl-C on the incoming stream of characters that is usually used for the REPL, in case that stream is used for other purposes. .. function:: schedule(func: Callable[[Any], Any], arg: Any) -> None Schedule the function *func* to be executed "very soon". The function is passed the value *arg* as its single argument. "Very soon" means that the MicroPython runtime will do its best to execute the function at the earliest possible time, given that it is also trying to be efficient, and that the following conditions hold: - A scheduled function will never preempt another scheduled function. - Scheduled functions are always executed "between opcodes" which means that all fundamental Python operations (such as appending to a list) are guaranteed to be atomic. - A given port may define "critical regions" within which scheduled functions will never be executed. Functions may be scheduled within a critical region but they will not be executed until that region is exited. An example of a critical region is a preempting interrupt handler (an IRQ). - Inside native code functions, scheduled functions are not called unless the native code calls a function that specifically does so. - Certain functions including ``poll.poll``, ``poll.ipoll``, ``time.sleep`` and ``time.sleep_ms`` (including zero-duration sleeps) will call scheduled functions. A use for this function is to schedule a callback from a preempting IRQ. Such an IRQ puts restrictions on the code that runs in the IRQ (for example the heap may be locked) and scheduling a function to call later will lift those restrictions. On multi-threaded ports, the scheduled function's behaviour depends on whether the Global Interpreter Lock (GIL) is enabled for the specific port: - If GIL is enabled, the function can preempt any thread and run in its context. - If GIL is disabled, the function will only preempt the main thread and run in its context. Note: If `schedule()` is called from a preempting IRQ, when memory allocation is not allowed and the callback to be passed to `schedule()` is a bound method, passing this directly will fail. This is because creating a reference to a bound method causes memory allocation. A solution is to create a reference to the method in the class constructor and to pass that reference to `schedule()`. This is discussed in detail here :ref:`reference documentation ` under "Creation of Python objects". There is a finite queue to hold the scheduled functions and `schedule()` will raise a `RuntimeError` if the queue is full. Classes ------- .. class:: RingIO(size: int) RingIO(buffer: Union[bytes, bytearray, memoryview]) Provides a fixed-size ringbuffer for bytes with a stream interface. Can be considered a FIFO-queue variant of `io.BytesIO`. The two constructor forms differ only in how the backing buffer is supplied: - ``RingIO(size)`` allocates the backing buffer internally. The classic ringbuffer algorithm reserves one byte for tracking, so the allocated buffer is one byte larger than ``size`` and the instance can hold the full ``size`` bytes of data. For example, ``RingIO(16)`` allocates a 17-byte buffer and holds 16 bytes of data. - ``RingIO(buffer)`` uses the supplied ``buffer`` in place rather than allocating one. Because one byte is reserved for tracking, the instance can hold ``len(buffer) - 1`` bytes of data. For example, ``RingIO(bytearray(16))`` holds 15 bytes of data. A RingIO instance is IRQ-/thread-safe when used to pass data in a single direction (for example written to from an IRQ and read from a non-IRQ function, or vice versa). This does not hold if a single instance is written to from both IRQ and non-IRQ contexts, which would often cause data corruption. .. method:: RingIO.any() -> int Returns an integer counting the number of characters that can be read. .. method:: RingIO.read(nbytes: Optional[int] = None) -> bytes Read available characters. This is a non-blocking function. If ``nbytes`` is specified then read at most that many bytes, otherwise read as much data as possible. Return value: a bytes object containing the bytes read. Will be zero-length bytes object if no data is available. .. method:: RingIO.readline(nbytes: Optional[int] = None) -> bytes Read a line, ending in a newline character or return if one exists in the buffer, else return available bytes in buffer. If ``nbytes`` is specified then read at most that many bytes. Return value: a bytes object containing the line read. .. method:: RingIO.readinto(buf: Union[bytearray, memoryview], nbytes: Optional[int] = None) -> int Read available bytes into the provided ``buf``. If ``nbytes`` is specified then read at most that many bytes. Otherwise, read at most ``len(buf)`` bytes. Return value: Integer count of the number of bytes read into ``buf``. .. method:: RingIO.write(buf: Union[bytes, bytearray, memoryview]) -> int Non-blocking write of bytes from ``buf`` into the ringbuffer, limited by the available space in the ringbuffer. Return value: Integer count of bytes written. .. method:: RingIO.close() -> None No-op provided as part of standard :std:term:`stream` interface. Has no effect on data in the ringbuffer.