circuitpython/docs/library/rp2.StateMachine.rst

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.. 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.