143 lines
4.8 KiB
ReStructuredText
143 lines
4.8 KiB
ReStructuredText
.. currentmodule:: rp2
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.. _rp2.StateMachine:
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class StateMachine -- access to the RP2040's programmable I/O interface
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=======================================================================
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The :class:`StateMachine` class gives access to the RP2040's PIO (programmable
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I/O) interface.
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For assembling PIO programs, see :func:`rp2.asm_pio`.
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Constructors
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------------
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.. class:: StateMachine(id, [program, ...])
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Get the state machine numbered *id*. The RP2040 has two identical PIO
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instances, each with 4 state machines: so there are 8 state machines in
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total, numbered 0 to 7.
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Optionally initialize it with the given program *program*: see
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`StateMachine.init`.
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Methods
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-------
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.. 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)
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Configure the state machine instance to run the given *program*.
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The program is added to the instruction memory of this PIO instance. If the
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instruction memory already contains this program, then its offset is
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reused so as to save on instruction memory.
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- *freq* is the frequency in Hz to run the state machine at. Defaults to
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the system clock frequency.
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The clock divider is computed as ``system clock frequency / freq``, so
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there can be slight rounding errors.
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The minimum possible clock divider is one 65536th of the system clock: so
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at the default system clock frequency of 125MHz, the minimum value of
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*freq* is ``1908``. To run state machines at slower frequencies, you'll
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need to reduce the system clock speed with `machine.freq()`.
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- *in_base* is the first pin to use for ``in()`` instructions.
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- *out_base* is the first pin to use for ``out()`` instructions.
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- *set_base* is the first pin to use for ``set()`` instructions.
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- *jmp_pin* is the first pin to use for ``jmp(pin, ...)`` instructions.
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- *sideset_base* is the first pin to use for side-setting.
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- *in_shiftdir* is the direction the ISR will shift, either
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`PIO.SHIFT_LEFT` or `PIO.SHIFT_RIGHT`.
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- *out_shiftdir* is the direction the OSR will shift, either
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`PIO.SHIFT_LEFT` or `PIO.SHIFT_RIGHT`.
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- *push_thresh* is the threshold in bits before auto-push or conditional
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re-pushing is triggered.
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- *pull_thresh* is the threshold in bits before auto-pull or conditional
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re-pulling is triggered.
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.. method:: StateMachine.active([value])
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Gets or sets whether the state machine is currently running.
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>>> sm.active()
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True
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>>> sm.active(0)
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False
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.. method:: StateMachine.restart()
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Restarts the state machine and jumps to the beginning of the program.
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This method clears the state machine's internal state using the RP2040's
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``SM_RESTART`` register. This includes:
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- input and output shift counters
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- the contents of the input shift register
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- the delay counter
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- the waiting-on-IRQ state
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- a stalled instruction run using `StateMachine.exec()`
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.. method:: StateMachine.exec(instr)
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Execute a single PIO instruction.
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If *instr* is a string then uses `asm_pio_encode` to encode the instruction
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from the given string.
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>>> sm.exec("set(0, 1)")
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If *instr* is an integer then it is treated as an already encoded PIO
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machine code instruction to be executed.
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>>> sm.exec(rp2.asm_pio_encode("out(y, 8)", 0))
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.. method:: StateMachine.get(buf=None, shift=0)
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Pull a word from the state machine's RX FIFO.
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If the FIFO is empty, it blocks until data arrives (i.e. the state machine
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pushes a word).
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The value is shifted right by *shift* bits before returning, i.e. the
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return value is ``word >> shift``.
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.. method:: StateMachine.put(value, shift=0)
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Push words onto the state machine's TX FIFO.
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*value* can be an integer, an array of type ``B``, ``H`` or ``I``, or a
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`bytearray`.
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This method will block until all words have been written to the FIFO. If
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the FIFO is, or becomes, full, the method will block until the state machine
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pulls enough words to complete the write.
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Each word is first shifted left by *shift* bits, i.e. the state machine
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receives ``word << shift``.
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.. method:: StateMachine.rx_fifo()
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Returns the number of words in the state machine's RX FIFO. A value of 0
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indicates the FIFO is empty.
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Useful for checking if data is waiting to be read, before calling
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`StateMachine.get()`.
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.. method:: StateMachine.tx_fifo()
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Returns the number of words in the state machine's TX FIFO. A value of 0
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indicates the FIFO is empty.
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Useful for checking if there is space to push another word using
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`StateMachine.put()`.
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.. method:: StateMachine.irq(handler=None, trigger=0|1, hard=False)
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Returns the IRQ object for the given StateMachine.
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Optionally configure it.
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