.. currentmodule:: rp2
.. _rp2.StateMachine:

class StateMachine -- access to the RP2040's programmable I/O interface
=======================================================================

The :class:`StateMachine` class gives access to the RP2040's PIO (programmable
I/O) interface.

For assembling PIO programs, see :func:`rp2.asm_pio`.


Constructors
------------

.. class:: StateMachine(id, [program, ...])

    Get the state machine numbered *id*. The RP2040 has two identical PIO
    instances, each with 4 state machines: so there are 8 state machines in
    total, numbered 0 to 7.

    Optionally initialize it with the given program *program*: see
    `StateMachine.init`.


Methods
-------

.. method:: StateMachine.init(program, freq=-1, *, in_base=None, out_base=None, set_base=None, jmp_pin=None, sideset_base=None, in_shiftdir=None, out_shiftdir=None, push_thresh=None, pull_thresh=None)

    Configure the state machine instance to run the given *program*.

    The program is added to the instruction memory of this PIO instance. If the
    instruction memory already contains this program, then its offset is
    re-used so as to save on instruction memory.

    - *freq* is the frequency in Hz to run the state machine at. Defaults to
      the system clock frequency.

      The clock divider is computed as ``system clock frequency / freq``, so
      there can be slight rounding errors.

      The minimum possible clock divider is one 65536th of the system clock: so
      at the default system clock frequency of 125MHz, the minimum value of
      *freq* is ``1908``. To run state machines at slower frequencies, you'll
      need to reduce the system clock speed with `machine.freq()`.
    - *in_base* is the first pin to use for ``in()`` instructions.
    - *out_base* is the first pin to use for ``out()`` instructions.
    - *set_base* is the first pin to use for ``set()`` instructions.
    - *jmp_pin* is the first pin to use for ``jmp(pin, ...)`` instructions.
    - *sideset_base* is the first pin to use for side-setting.
    - *in_shiftdir* is the direction the ISR will shift, either
      `PIO.SHIFT_LEFT` or `PIO.SHIFT_RIGHT`.
    - *out_shiftdir* is the direction the OSR will shift, either
      `PIO.SHIFT_LEFT` or `PIO.SHIFT_RIGHT`.
    - *push_thresh* is the threshold in bits before auto-push or conditional
      re-pushing is triggered.
    - *pull_thresh* is the threshold in bits before auto-push or conditional
      re-pushing is triggered.

.. method:: StateMachine.active([value])

    Gets or sets whether the state machine is currently running.

    >>> sm.active()
    True
    >>> sm.active(0)
    False

.. method:: StateMachine.restart()

    Restarts the state machine and jumps to the beginning of the program.

    This method clears the state machine's internal state using the RP2040's
    ``SM_RESTART`` register. This includes:

     - input and output shift counters
     - the contents of the input shift register
     - the delay counter
     - the waiting-on-IRQ state
     - a stalled instruction run using `StateMachine.exec()`

.. method:: StateMachine.exec(instr)

    Execute a single PIO instruction. Uses `asm_pio_encode` to encode the
    instruction from the given string *instr*.

    >>> sm.exec("set(0, 1)")

.. method:: StateMachine.get(buf=None, shift=0)

    Pull a word from the state machine's RX FIFO.

    If the FIFO is empty, it blocks until data arrives (i.e. the state machine
    pushes a word).

    The value is shifted right by *shift* bits before returning, i.e. the
    return value is ``word >> shift``.

.. method:: StateMachine.put(value, shift=0)

    Push a word onto the state machine's TX FIFO.

    If the FIFO is full, it blocks until there is space (i.e. the state machine
    pulls a word).

    The value is first shifted left by *shift* bits, i.e. the state machine
    receives ``value << shift``.

.. method:: StateMachine.rx_fifo()

    Returns the number of words in the state machine's RX FIFO. A value of 0
    indicates the FIFO is empty.

    Useful for checking if data is waiting to be read, before calling
    `StateMachine.get()`.

.. method:: StateMachine.tx_fifo()

    Returns the number of words in the state machine's TX FIFO. A value of 0
    indicates the FIFO is empty.

    Useful for checking if there is space to push another word using
    `StateMachine.put()`.

.. method:: StateMachine.irq(handler=None, trigger=0|1, hard=False)

     Returns the IRQ object for the given StateMachine.

     Optionally configure it.

