Add full-fledged documentation, update I2S API (#80)

Last step before 1.0. Docs for readthedocs.io.

Update the I2S API to mimic others where `setXXX` is called before
`begin()` to set the GPIO pins used.

docs/Makefile

@@ -0,0 +1,20 @@
+# Minimal makefile for Sphinx documentation
+#
+
+# You can set these variables from the command line.
+SPHINXOPTS    =
+SPHINXBUILD   = sphinx-build
+SPHINXPROJ    = Arduino-Pico
+SOURCEDIR     = .
+BUILDDIR      = _build
+
+# Put it first so that "make" without argument is like "make help".
+help:
+	@$(SPHINXBUILD) -M help "$(SOURCEDIR)" "$(BUILDDIR)" $(SPHINXOPTS) $(O)
+
+.PHONY: help Makefile
+
+# Catch-all target: route all unknown targets to Sphinx using the new
+# "make mode" option.  $(O) is meant as a shortcut for $(SPHINXOPTS).
+%: Makefile
+	@$(SPHINXBUILD) -M $@ "$(SOURCEDIR)" "$(BUILDDIR)" $(SPHINXOPTS) $(O)

docs/analog.rst

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+Analog I/O
+==========
+
+Analog Input
+------------
+For analog inputs, the RP2040 device has a 12-bit, 4-channel ADC +
+temperature sensor available on a fixed set of pins (A0...A3).
+The standard Arduino calls can be used to read their values (with
+3.3V nominally reading as 4095).
+
+int analogRead(pin_size_t pin = A0..A3)
+---------------------------------------
+Returns a value from 0...4095 correspionding to the ADC reading
+of the specific pin.
+
+float analogReadTemp()
+----------------------
+Returns the temperature, in Celsius, of the onboard thermal sensor.
+This reading is not exceedingly accurate and of relatively low
+resolution, so it is not a replacement for an external temperature
+sensor in many cases.
+
+Analog Outputs
+--------------
+The RP2040 does not have any onboard DACs, so analog outputs are
+simulated using the standard method of using pulse width modulation
+(PWM) using the RP20400's hardware PWM units.
+
+While up to 16 PWM channels can be generated, they are not independent
+and there are significant restrictions as to allowed pins in parallel.
+See the [RP2040 datasheet](https://datasheets.raspberrypi.org/rp2040/rp2040-datasheet.pdf)
+for full details.
+
+void analogWriteFreq(uint32_t freq)
+-----------------------------------
+Sets the master PWM frequency used (i.e. how often the PWM output cycles).
+From 100Hz to 60KHz are supported.
+}
+
+void analogWriteRange(uint32_t range) and analogWriteResolution(int res)
+------------------------------------------------------------------------
+These calls set the maximum PWM value (i.e. writing this value will result in
+a PWM duty cycle of 100%)/ either explicitly (range) or as a power-of-two
+(res).  A range of 16 to 65535 is supported.
+
+void analogWrite(pin_size_t pin, int val)
+-----------------------------------------
+Writes a PWM value to a specific pin.  The PWM machine is enabled and set to
+the requested frequency and scale, and the output is generated.  This will
+continue until a `digitalWrite` or other digital output is performed.

docs/conf.py

@@ -0,0 +1,168 @@
+# -*- coding: utf-8 -*-
+#
+# Arduino-Pico documentation build configuration file, created by
+# sphinx-quickstart on Sat Apr  3 15:02:21 2021.
+#
+# This file is execfile()d with the current directory set to its
+# containing dir.
+#
+# Note that not all possible configuration values are present in this
+# autogenerated file.
+#
+# All configuration values have a default; values that are commented out
+# serve to show the default.
+
+# If extensions (or modules to document with autodoc) are in another directory,
+# add these directories to sys.path here. If the directory is relative to the
+# documentation root, use os.path.abspath to make it absolute, like shown here.
+#
+# import os
+# import sys
+# sys.path.insert(0, os.path.abspath('.'))
+
+
+# -- General configuration ------------------------------------------------
+
+# If your documentation needs a minimal Sphinx version, state it here.
+#
+# needs_sphinx = '1.0'
+
+# Add any Sphinx extension module names here, as strings. They can be
+# extensions coming with Sphinx (named 'sphinx.ext.*') or your custom
+# ones.
+extensions = []
+
+# Add any paths that contain templates here, relative to this directory.
+templates_path = ['_templates']
+
+# The suffix(es) of source filenames.
+# You can specify multiple suffix as a list of string:
+#
+# source_suffix = ['.rst', '.md']
+source_suffix = '.rst'
+
+# The master toctree document.
+master_doc = 'index'
+
+# General information about the project.
+project = u'Arduino-Pico'
+copyright = u'2021, Earle F. Philhower, III'
+author = u'Earle F. Philhower, III'
+
+# The version info for the project you're documenting, acts as replacement for
+# |version| and |release|, also used in various other places throughout the
+# built documents.
+#
+# The short X.Y version.
+version = u'1.0.0'
+# The full version, including alpha/beta/rc tags.
+release = u'1.0.0'
+
+# The language for content autogenerated by Sphinx. Refer to documentation
+# for a list of supported languages.
+#
+# This is also used if you do content translation via gettext catalogs.
+# Usually you set "language" from the command line for these cases.
+language = None
+
+# List of patterns, relative to source directory, that match files and
+# directories to ignore when looking for source files.
+# This patterns also effect to html_static_path and html_extra_path
+exclude_patterns = ['_build', 'Thumbs.db', '.DS_Store']
+
+# The name of the Pygments (syntax highlighting) style to use.
+pygments_style = 'sphinx'
+
+# If true, `todo` and `todoList` produce output, else they produce nothing.
+todo_include_todos = False
+
+
+# -- Options for HTML output ----------------------------------------------
+
+# The theme to use for HTML and HTML Help pages.  See the documentation for
+# a list of builtin themes.
+#
+html_theme = 'alabaster'
+
+# Theme options are theme-specific and customize the look and feel of a theme
+# further.  For a list of options available for each theme, see the
+# documentation.
+#
+# html_theme_options = {}
+
+# Add any paths that contain custom static files (such as style sheets) here,
+# relative to this directory. They are copied after the builtin static files,
+# so a file named "default.css" will overwrite the builtin "default.css".
+html_static_path = ['_static']
+
+# Custom sidebar templates, must be a dictionary that maps document names
+# to template names.
+#
+# This is required for the alabaster theme
+# refs: http://alabaster.readthedocs.io/en/latest/installation.html#sidebars
+html_sidebars = {
+    '**': [
+        'relations.html',  # needs 'show_related': True theme option to display
+        'searchbox.html',
+    ]
+}
+
+
+# -- Options for HTMLHelp output ------------------------------------------
+
+# Output file base name for HTML help builder.
+htmlhelp_basename = 'Arduino-Picodoc'
+
+
+# -- Options for LaTeX output ---------------------------------------------
+
+latex_elements = {
+    # The paper size ('letterpaper' or 'a4paper').
+    #
+    # 'papersize': 'letterpaper',
+
+    # The font size ('10pt', '11pt' or '12pt').
+    #
+    # 'pointsize': '10pt',
+
+    # Additional stuff for the LaTeX preamble.
+    #
+    # 'preamble': '',
+
+    # Latex figure (float) alignment
+    #
+    # 'figure_align': 'htbp',
+}
+
+# Grouping the document tree into LaTeX files. List of tuples
+# (source start file, target name, title,
+#  author, documentclass [howto, manual, or own class]).
+latex_documents = [
+    (master_doc, 'Arduino-Pico.tex', u'Arduino-Pico Documentation',
+     u'Earle F. Philhower, III', 'manual'),
+]
+
+
+# -- Options for manual page output ---------------------------------------
+
+# One entry per manual page. List of tuples
+# (source start file, name, description, authors, manual section).
+man_pages = [
+    (master_doc, 'arduino-pico', u'Arduino-Pico Documentation',
+     [author], 1)
+]
+
+
+# -- Options for Texinfo output -------------------------------------------
+
+# Grouping the document tree into Texinfo files. List of tuples
+# (source start file, target name, title, author,
+#  dir menu entry, description, category)
+texinfo_documents = [
+    (master_doc, 'Arduino-Pico', u'Arduino-Pico Documentation',
+     author, 'Arduino-Pico', 'One line description of project.',
+     'Miscellaneous'),
+]
+
+
+

docs/digital.rst

@@ -0,0 +1,6 @@
+Digital I/O
+===========
+
+The Raspberry Pi Pico RP2040 chip supports up to 30 digital I/O pins,
+however not all boards provide access to all pins.
+

docs/eeprom.rst

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+EEPROM Library
+==============
+
+While the Raspberry Pi Pico RP2040 does not come with an EEPROM onboard, we
+simulate one by using a single 4K chunk of flash at the end of flash space.
+
+**Note that this is a simulated EEPROM and will only support the numeber of
+writes as the onboard flash chip, not the 100,000 or so of a real EEPROM.**
+Therefore, do not frequently update the EEPROM or you may prematurely wear
+out the flash.
+
+EEPROM.begin(size=256...4096)
+-----------------------------
+Call before the first use of the EEPROM data for read or write.  It makes a
+copy of the emulated EEPROM sector in RAM to allow random update and access.
+
+EEPROM.read(addr), EEPROM[addr]
+-------------------------------
+Returns the data at a specific offset in the EEPROM. See `EEPROM.get` later
+for a more 
+
+EEPROM.write(addr, data), EEPROM[addr] = data
+---------------------------------------------
+Writes a byte of data at the offset specified.  Not persisted to flash until
+`EEPROM.commit()` is called.
+
+EEPROM.commit()
+---------------
+Writes the updated data to flash, so next reboot it will be readable.
+
+EEPROM.end()
+------------
+`EEPROM.commit()` and frees all memory used.  Need to call `EEPROM.begin()`
+before the EEPROM can be used again.
+
+EEPROM.get(addr, val)
+---------------------
+Copies the (potentially multi-byte) data in EEPROM at the specific byte
+offset into the returned value.  Useful for reading structures from EEPROM.
+
+EEPROM.put(addr, val)
+---------------------
+Copies the (potentially multi-byte) value into EEPROM a the byte offset
+supplied.  Useful for storing `struct` in EEPROM.  Note that any pointers
+inside a written structure will not be valid, and that most C++ objects
+like `String` cannot be written to EEPROM this way because of it.
+
+EEPROM.length()
+---------------
+Returns the length of the EEPROM (i.e. the value specified in
+`EEPROM.begin()` ).
+
+EEPROM Examples
+---------------
+Three EEPROM [examples](https://github.com/earlephilhower/arduino-pico/tree/master/libraries/EEPROM) are included.