docs/library/machine: Add docs for Counter and Encoder.

Add documentation for `machine.Counter` and `machine.Encoder` as currently
implemented by the esp32 port, but intended to be implemented by other
ports.

Originally authored by: Ihor Nehrutsa <Ihor.Nehrutsa@gmail.com> and
Jonathan Hogg <me@jonathanhogg.com>.

Signed-off-by: Jim Mussared <jim.mussared@gmail.com>

1 files changed, 15 insertions, 0 deletions

diff --git a/docs/esp32/quickref.rst b/docs/esp32/quickref.rst
index 7127cc402..2c667a0f0 100644
--- a/docs/esp32/quickref.rst
+++ b/docs/esp32/quickref.rst
@@ -587,6 +587,21 @@ Use the :ref:`esp32.PCNT <esp32.PCNT>` class::
 The PCNT hardware supports monitoring multiple pins in a single unit to
 implement quadrature decoding or up/down signal counters.
 
+See the :ref:`machine.Counter <machine.Counter>` and
+:ref:`machine.Encoder <machine.Encoder>` classes for simpler abstractions of
+common pulse counting applications::
+
+    from machine import Pin, Counter
+
+    counter = Counter(0, Pin(2))    # create a counter as above and start it
+    count = counter.value()         # read the count as an arbitrary precision signed integer
+
+    encoder = Encoder(0, Pin(12), Pin(14))    # create an encoder and begin counting
+    count = encoder.value()                   # read the count as an arbitrary precision signed integer
+
+Note that the id passed to these ``Counter()`` and ``Encoder()`` objects must be
+a PCNT id.
+
 Software SPI bus
 ----------------