docs/rp2: Add reference for PIO assembly instructions, and PIO tutorial.

1 files changed, 152 insertions, 0 deletions

diff --git a/docs/library/rp2.rst b/docs/library/rp2.rst
index 5d168bce2..43143fe08 100644
--- a/docs/library/rp2.rst
+++ b/docs/library/rp2.rst
@@ -72,6 +72,158 @@ For running PIO programs, see :class:`rp2.StateMachine`.
     an error assembling a PIO program.
 
 
+PIO assembly language instructions
+----------------------------------
+
+PIO state machines are programmed in a custom assembly language with nine core
+PIO-machine instructions.  In MicroPython, PIO assembly routines are written as
+a Python function with the decorator ``@rp2.asm_pio()``, and they use Python
+syntax.  Such routines support standard Python variables and arithmetic, as well
+as the following custom functions that encode PIO instructions and direct the
+assembler.  See sec 3.4 of the RP2040 datasheet for further details.
+
+wrap_target()
+    Specify the location where execution continues after program wrapping.
+    By default this is the start of the PIO routine.
+
+wrap()
+    Specify the location where the program finishes and wraps around.
+    If this directive is not used then it is added automatically at the end of
+    the PIO routine.  Wrapping does not cost any execution cycles.
+
+label(label)
+    Define a label called *label* at the current location.  *label* can be a
+    string or integer.
+
+word(instr, label=None)
+    Insert an arbitrary 16-bit word in the assembled output.
+
+    - *instr*: the 16-bit value
+    - *label*: if given, look up the label and logical-or the label's value with
+      *instr*
+
+jmp(...)
+    This instruction takes two forms:
+
+    jmp(label)
+        - *label*: label to jump to unconditionally
+
+    jmp(cond, label)
+        - *cond*: the condition to check, one of:
+
+            - ``not_x``, ``not_y``: true if register is zero
+            - ``x_dec``, ``y_dec``: true if register is non-zero, and do post
+              decrement
+            - ``x_not_y``: true if X is not equal to Y
+            - ``pin``: true if the input pin is set
+            - ``not_osre``: true if OSR is not empty (hasn't reached its
+              threshold)
+
+        - *label*: label to jump to if condition is true
+
+wait(polarity, src, index)
+    Block, waiting for high/low on a pin or IRQ line.
+
+    - *polarity*: 0 or 1, whether to wait for a low or high value
+    - *src*: one of: ``gpio`` (absolute pin), ``pin`` (pin relative to
+      StateMachine's ``in_base`` argument), ``irq``
+    - *index*: 0-31, the index for *src*
+
+in_(src, bit_count)
+    Shift data in from *src* to ISR.
+
+    - *src*: one of: ``pins``, ``x``, ``y``, ``null``, ``isr``, ``osr``
+    - *bit_count*: number of bits to shift in (1-32)
+
+out(dest, bit_count)
+    Shift data out from OSR to *dest*.
+
+    - *dest*: one of: ``pins``, ``x``, ``y``, ``pindirs``, ``pc``, ``isr``,
+      ``exec``
+    - *bit_count*: number of bits to shift out (1-32)
+
+push(...)
+    Push ISR to the RX FIFO, then clear ISR to zero.
+    This instruction takes the following forms:
+
+    - push()
+    - push(block)
+    - push(noblock)
+    - push(iffull)
+    - push(iffull, block)
+    - push(iffull, noblock)
+
+    If ``block`` is used then the instruction stalls if the RX FIFO is full.
+    The default is to block.  If ``iffull`` is used then it only pushes if the
+    input shift count has reached its threshold.
+
+pull(...)
+    Pull from the TX FIFO into OSR.
+    This instruction takes the following forms:
+
+    - pull()
+    - pull(block)
+    - pull(noblock)
+    - pull(ifempty)
+    - pull(ifempty, block)
+    - pull(ifempty, noblock)
+
+    If ``block`` is used then the instruction stalls if the TX FIFO is empty.
+    The default is to block.  If ``ifempty`` is used then it only pulls if the
+    output shift count has reached its threshold.
+
+mov(dest, src)
+    Move into *dest* the value from *src*.
+
+    - *dest*: one of: ``pins``, ``x``, ``y``, ``exec``, ``pc``, ``isr``, ``osr``
+    - *src*: one of: ``pins``, ``x``, ``y``, ``null``, ``status``, ``isr``,
+      ``osr``; this argument can be optionally modified by wrapping it in
+      ``invert()`` or ``reverse()`` (but not both together)
+
+irq(...)
+    Set or clear an IRQ flag.
+    This instruction takes two forms:
+
+    irq(index)
+        - *index*: 0-7, or ``rel(0)`` to ``rel(7)``
+
+    irq(mode, index)
+        - *mode*: one of: ``block``, ``clear``
+        - *index*: 0-7, or ``rel(0)`` to ``rel(7)``
+
+    If ``block`` is used then the instruction stalls until the flag is cleared
+    by another entity.  If ``clear`` is used then the flag is cleared instead of
+    being set.  Relative IRQ indices add the state machine ID to the IRQ index
+    with modulo-4 addition.  IRQs 0-3 are visible from to the processor, 4-7 are
+    internal to the state machines.
+
+set(dest, data)
+    Set *dest* with the value *data*.
+
+    - *dest*: ``pins``, ``x``, ``y``, ``pindirs``
+    - *data*: value (0-31)
+
+nop()
+    This is a pseudoinstruction that assembles to ``mov(y, y)`` and has no side
+    effect.
+
+.side(value)
+    This is a modifier which can be applied to any instruction, and is used to
+    control side-set pin values.
+
+    - *value*: the value (bits) to output on the side-set pins
+
+.delay(value)
+    This is a modifier which can be applied to any instruction, and specifies
+    how many cycles to delay for after the instruction executes.
+
+    - *value*: cycles to delay, 0-31 (maximum value reduced if side-set pins are
+      used)
+
+[value]
+    This is a modifier and is equivalent to ``.delay(value)``.
+
+
 Classes
 -------