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

+# 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)
\ No newline at end of file

docs/analog.rst

+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

+# -*- 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

+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

+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.

docs/help.rst

+Getting Help and Contributing
+=============================
+
+This is a community supported project and has multiple ways to get assistance.
+Posting complete details, in a polite and organized way will get the best
+response.
+
+For bugs in the Core, or to submit patches, please use the
+[GitHub Issues](https://github.com/earlephilhower/arduino-pico/issues) or
+[GitHub Pull Requests](https://github.com/earlephilhower/arduino-pico/pulls)
+
+For general questions/discussions use either [GitHub Discussions](https://github.com/earlephilhower/arduino-pico/discussions)
+or live-chat with [gitter](https://gitter.im/arduino-pico/community)
+

docs/i2s.rst

+I2S (Digital Audio) Output Library
+==================================
+
+While the RP2040 chip on the Raspberry Pi Pico does not include a hardware
+I2S device, it is possible to use the PIO (Programmable I/O) state machines
+to implement one dynamically.
+
+This I2S library uses the `pico-extras` I2S audio library and wraps it in
+an Arduino I2S library.  It supports 16 bits/sample and frequencies of up
+to 48kHZ, with configurable BCLK, LRCLK(always pin "BCLK + 1"), and DOUT pins.
+
+**Note:** This I2S device takes over the entire PIO1 (second) unit and adjusts
+its clock frequency to meet the I2S needs.  That means when only 4 Tones
+or only 4 Servos may be used when the I2S device is used.
+
+bool setBCLK(pin_size_t pin)
+----------------------------
+Sets the BCLK pin of the I2S device.  The LRCLK/word clock will be `pin + 1`
+due to limitations of the PIO state machines.  Call this before `I2S.begin()`
+Default BCLK = 26, LRCLK = 27
+
+bool setDOUT(pin_size_t pin)
+----------------------------
+Sets the DOUT pin of the I2S device.  Any pin may be used.  Default DOUT = 28
+Call before `I2S.begin()`
+
+bool begin(long sampleRate)
+---------------------------
+Start the I2S device up with the given sample rate.  The pins selected above
+will be turned to output and the I2S will begin to drive silence frames (all
+zero) out.
+
+void end()
+----------
+Stops the I2S device.  **Note, at present the memory allocated for I2S buffers
+is not freed leading to a memory leak when `end()` is called.  This is due
+to the state of the `pico-extras` release from thich this device came.**
+
+void flush()
+------------
+Sends any partial frames in memory to the I2S output device.  They may NOT play
+immediately.  Potential use case for this call would be when the frequency of
+the output will be changing.
+
+size_t write(uint8_t)
+---------------------
+Provided for compatibilty, but not very useful.  Writes a sample from 0...255
+to the I2S buffer.  See `write(int16_t)` for a better one
+
+size_t write(const uint8_t \*buffer, size_t size)
+-------------------------------------------------
+Transfers number of bytes from an application buffer to the I2S output buffer.
+Be aware that `size` is in *bytes** and not samples.  Size must be a multiple
+of **4 bytes** (i.e. one left/right sample).  Will not block, so check
+the return value to find out how many bytes were actually written.
+
+int availableForWrite()
+-----------------------
+Returns the number of **32-bit L/R samples** that can be written without
+potentially blocking.
+
+bool setFrequency(int newFreq)
+------------------------------
+Adjusts the I2S output frequency.  When changing frequency while I2S output
+is underway, be sure to use `I2S.flush()` before changing the frequency to
+ensure the older data is played at the right frequency.
+
+
+size_t write(int16_t)
+---------------------
+Writes a single 16-bit left or right sample to the I2S output buffer.  The
+user is required to ensure that an even number of samples is written (i.e.
+left and right) over the application lifetime.  The application also needs
+to track which sample is next to be written (right/left).  For this reason,
+the `write(void *b, size_t lrsamples)` call may be easier and faster to use.
+
+size_t write(const void \*buffer, size_t lrsamples)
+---------------------------------------------------
+Writes up to size left+right packed samples to the I2S device.  Non-blocking,
+will writefrom 0...size samples and return that count.  Be sure your app
+handles partial writes (i.e. by yield()ing and then retrying to write the
+remaining data.)
+
+The `onTransmit` callback is not supported.
+
+See the [ESP8266Audio](https://github.com/earlephilhower/ESP8266Audio) library
+for a working example, or look at the included sample tone generator.

docs/ide.rst

+IDE Menus
+=========
+
+Model
+-----
+Use the boards menu to select your model of RP2040 board.  There will be two
+options:  `Boardname` and `Boardname (Picoprobe)`.  If you want to use a
+Picoprobe to upload your sketches and not the default automatic UF2 upload,
+use the `(Picoprobe)` option, otherwise use the normal name.  No functional
+or code changes are done because of this.
+
+There is also a `Generic` board which allows you to individually select
+things such as flash size or boot2 flash type.  Use this if your board isn't
+yet fully supported and isn't working with the normal `Raspberry Pi Pico`
+option.
+
+Flash Size
+----------
+Arduino-Pico supports onboard filesystems which will set aside some of the
+flash on your board for the filesystem, shrinking the maximum code size
+allowed.  Use this menu to select the desired ratio of filesystem to sketch.
+
+CPU Speed
+---------
+While it is unsupported, the Raspberry Pi Pico RP2040 can often run much
+faster than the stock 125MHz.  Use the `CPU Speed` menu to select a
+desired over or underclock speed.  **If the sketch fails at the higher
+speed, hold the BOOTSEL while plugging it in to enter update mode and try
+a lower overclock.**
+
+Debug Port and Debug Level
+--------------------------
+Debug messages from `printf` and the Core can be printed to a Serial port
+to allow for easier debugging.  Select the desired port and verbosity.
+Selecting a port for debug output does not stop a sketch from using it
+for normal operations.

docs/index.rst

+Arduino-Pico
+============
+
+This is the documentation for the Raspberry Pi Pico Arduino core,
+Arduino-Pico.  Arduino-Pico is a community port of the RP2040
+(Raspberry Pi Pico processor) to the Arduino ecosystem, intended
+to make it easier and more fun to use and program the Raspberry Pi
+Pico / RP2040 based boards.
+
+This Arduino core uses a custom toolset with GCC 10.2 and Newlib 4.0.0
+and doesn't require any system-installed prerequisites.
+
+For the latest version, always check https://github.com/earlephilhower/arduino-pico
+
+.. toctree::
+   :maxdepth: 2
+   :caption: Contents:
+
+   Getting Help and Contributing <help>
+   Installation <install>
+   Using the IDE <ide>
+
+   Pin (Re)Assignment <pins>
+
+   Analog I/O <analog>
+   Digital I/O <digital>
+   EEPROM <eeprom>
+   I2S Audio <i2s>
+   Serial USB and UARTs <serial>
+   Servo <servo>
+   SPI <spi>
+   Wire(I2C) <wire>
+   File Systems (SD, SDFS, LittleFS) <fs>
+
+   Ported/Optimized Libraries <libraries>
+
+   Using Pico-SDK <sdk>
+
+   Licenses <license>
+
+Indices and Tables
+==================
+
+* :ref:`genindex`
+* :ref:`modindex`
+* :ref:`search`

docs/install.rst

+Intallation
+===========
+
+The Arduino-Pico core can be installed using the Arduino IDE Boards Manager
+or using `git`.  If you want to simply write programs for your RP2040 board,
+the Boards Manager installation will suffice, but if you want to try the
+latest pre-release versions and submit improvements, you will need the `git`
+instllation.
+
+Installing via Arduino Boards Manager
+-------------------------------------
+**Note for Windows Users**: Please do not use the Windows Store version of
+the actual Arduino application because it has issues detecting attached Pico
+boards.  Use the "Windows ZIP" or plain "Windows" executable (EXE) download
+direct from https://arduino.cc. and allow it to install any device drivers
+it suggests.  Otherwise the Pico board may not be detected.  Also, if trying
+out the 2.0 beta Arduino please install the release 1.8 version beforehand
+to ensure needed device drivers are present.
+
+1. Open up the Arduino IDE and go to File->Preferences.
+2. In the dialog that pops up, enter the following URL in the "Additional Boards Manager URLs" field:  https://github.com/earlephilhower/arduino-pico/releases/download/global/package_rp2040_index.json
+   .. image:: images/install1.png
+3. Hit OK to close the dialog.
+4. Go to Tools->Boards->Board Manager in the IDE
+5. Type "pico" in the search box and select "Add":
+   .. image:: images/install2.png
+
+Installing via GIT
+------------------
+To install via GIT (for latest and greatest versions):
+
+.. code:: bash
+
+        mkdir -p ~/Arduino/hardware/pico
+        git clone https://github.com/earlephilhower/arduino-pico.git ~/Arduino/hardware/pico/rp2040
+        cd ~/Arduino/hardware/pico/rp2040
+        git submodule update --init
+        cd pico-sdk
+        git submodule update --init
+        cd pico-extras
+        git submodule update --init
+        cd ../tools
+        python3 ./get.py
+
+Installing both Arduino and CMake
+---------------------------------
+Tom's Hardware presented a very nice writeup on installing `arduino-pico` on
+both Windows and Linux, available at [Tom's Hardware](https://www.tomshardware.com/how-to/program-raspberry-pi-pico-with-arduino-ide)
+
+If you follow their step-by-step you will also have a fully functional
+`CMake`-based environment to build Pico apps on if you outgrow the Arduino
+ecosystem.
+
+Uploading Sketches
+
+To upload your first sketch, you will need to hold the BOOTSEL button down while plugging in the Pico to your computer.
+Then hit the upload button and the sketch should be transferred and start to run.
+
+After the first upload, this should not be necessary as the `arduino-pico` core has auto-reset support. 
+Select the appropriate serial port shown in the Arduino Tools->Port->Serial Port menu once (this setting will stick and does not need to be
+touched for multiple uploads).   This selection allows the auto-reset tool to identify the proper device to reset.
+Them hit the upload button and your sketch should upload and run.
+
+In some cases the Pico will encounter a hard hang and its USB port will not respond to the auto-reset request.  Should this happen, just
+follow the initial procedure of holding the BOOTSEL button down while plugging in the Pico to enter the ROM bootloader.
+
+# Uploading Filesystem Images
+The onboard flash filesystem for the Pico, LittleFS, lets you upload a filesystem image from the sketch directory for your sketch to use.  Download the needed plugin from
+* https://github.com/earlephilhower/arduino-pico-littlefs-plugin/releases
+
+To install, follow the directions in 
+* https://github.com/earlephilhower/arduino-pico-littlefs-plugin/blob/master/README.md 
+
+For detailed usage information, please check the ESP8266 repo documentation (ignore SPIFFS related notes) available at
+* https://arduino-esp8266.readthedocs.io/en/latest/filesystem.html
+
+# Uploading Sketches with Picoprobe
+If you have built a Raspberry Pi Picoprobe, you can use OpenOCD to handle your sketch uploads and for debugging with GDB.
+
+Under Windows a local admin user should be able to access the Picoprobe port automatically, but under Linux `udev` must be told about the device and to allow normal users access.
+
+To set up user-level access to Picoprobes on Ubuntu (and other OSes which use `udev`):
+
+.. code::
+
+        echo 'SUBSYSTEMS=="usb", ATTRS{idVendor}=="2e8a", ATTRS{idProduct}=="0004", GROUP="users", MODE="0666"' | sudo tee -a /etc/udev/rules.d/98-PicoProbe.rules
+        sudo udevadm control --reload
+
+The first line creates a file with the USB vendor and ID of the Picoprobe and tells UDEV to give users full access to it.  The second causes `udev` to load this new rule.  Note that you will need to unplug and re-plug in your device the first time you create this file, to allow udev to make the device node properly.
+
+Once Picoprobe permissions are set up properly, then select the board "Raspberry Pi Pico (Picoprobe)" in the Tools menu and upload as normal.
+
+# Debugging with Picoprobe, OpenOCD, and GDB
+The installed tools include a version of OpenOCD (in the pqt-openocd directory) and GDB (in the pqt-gcc directory).  These may be used to run GDB in an interactive window as documented in the Pico Getting Started manuals from the Raspberry Pi Foundation.

docs/libraries.rst

+Libraries Ported/Optimizef for the RP2040
+=========================================
+
+Most Arduino libraries that work on modern 32-bit CPU based Arduino boards
+will run fine using Arduino-Pico.
+
+The following libraries have undergone additional porting and optimizations
+specifically for the RP2040 and you should consider using them instead of
+the generic versions available in the Library Manager
+
+* [Adafruit GFX Library](https://github.com/Bodmer/Adafruit-GFX-Library) by @Bodmer, 2-20x faster than the standard version on the Pico
+* [Adafruit ILI9341 Library](https://github.com/Bodmer/Adafruit_ILI9341), again by @Bodmer
+* [ESP8266Audio](https://github.com/earlephilhower/ESP8266Audio), ported to use the included `I2S` library

docs/license.rst

+Licensing and Credits
+=====================
+
+Arduino-Pico is licensed under the LGPL license as detailed in the included README.
+
+In addition, it contains code from additional open source projects:
+
+* The [Arduino IDE and ArduinoCore-API](https://arduino.cc) are developed and maintained by the Arduino team. The IDE is licensed under GPL.
+* The [RP2040 GCC-based toolchain](https://github.com/earlephilhower/pico-quick-toolchain) is licensed under under the GPL.
+* The [Pico-SDK](https://github.com/raspberrypi/pico-sdk) and [Pico-Extras](https://github.com/raspberrypi/pico-extras) are by Raspberry Pi (Trading) Ltd and licensed under the BSD 3-Clause license.
+* [Arduino-Pico](https://github.com/earlephilhower/arduino-pico) core files are licenses under the LGPL.
+* [LittleFS](https://github.com/ARMmbed/littlefs) library written by ARM Limited and released under the [BSD 3-clause license](https://github.com/ARMmbed/littlefs/blob/master/LICENSE.md).
+* [UF2CONV.PY](https://github.com/microsoft/uf2) is by Microsoft Corporatio and licensed under the MIT license.
+* Some filesystem code taken from the [ESP8266 Arduino Core](https://github.com/esp8266/Arduino) and licensed under the LGPL.

docs/make.bat

+@ECHO OFF
+
+pushd %~dp0
+
+REM Command file for Sphinx documentation
+
+if "%SPHINXBUILD%" == "" (
+	set SPHINXBUILD=sphinx-build
+)
+set SOURCEDIR=.
+set BUILDDIR=_build
+set SPHINXPROJ=Arduino-Pico
+
+if "%1" == "" goto help
+
+%SPHINXBUILD% >NUL 2>NUL
+if errorlevel 9009 (
+	echo.
+	echo.The 'sphinx-build' command was not found. Make sure you have Sphinx
+	echo.installed, then set the SPHINXBUILD environment variable to point
+	echo.to the full path of the 'sphinx-build' executable. Alternatively you
+	echo.may add the Sphinx directory to PATH.
+	echo.
+	echo.If you don't have Sphinx installed, grab it from
+	echo.http://sphinx-doc.org/
+	exit /b 1
+)
+
+%SPHINXBUILD% -M %1 %SOURCEDIR% %BUILDDIR% %SPHINXOPTS%
+goto end
+
+:help
+%SPHINXBUILD% -M help %SOURCEDIR% %BUILDDIR% %SPHINXOPTS%
+
+:end
+popd

docs/pins.rst

+Pin Assignments
+===============
+
+The Raspberry Pi Pico has an incredibly flexible I/O configuration and most
+built-in peripherals (except for the ADC) can be used on multiple sets of
+pins.  Note, however, that not all peripherals can use all I/Os.  Refer to
+the RP2040 datasheet or an online pinout diagram for more details.
+
+Additional methods have been added to allow you to select a peripheral's
+I/O pins **before calling ::begin**.  This is especially helpful when
+using third party libraries:  the library doesn't need to be modified,
+only your own code in `setup()` is needed to adjust pinouts.
+
+I2S:
+----
+
+.. code:: cpp
+
+        ::setBCLK(pin)
+        ::setDOUT(pin)
+
+Serial1 (UART0), Serial2 (UART1):
+---------------------------------
+
+.. code:: cpp
+
+        ::setRX(pin)
+        ::setTX(pin)
+
+SPI (SPI0), SPI1 (SPI1):
+------------------------
+
+.. code:: cpp
+
+        ::setSCK(pin)
+        ::setRX(pin)
+        ::setTX(pin)
+
+Wire (I2C0), Wire1 (I2C1):
+--------------------------
+
+.. code:: cpp
+
+        ::setSDA(pin)
+        ::setSCL(pin)
+
+
+For example, because the `SD` library uses the `SPI` library, we can make
+it use a non-default pinout with a simple call
+
+.. code:: cpp
+
+    void setup() {
+        SPI.setRX(4);
+        SPI.setTX(7);
+        SPI.setSCK(6);
+        SPI.setCS(5);
+        SD.begin(5);
+    }
+

docs/sdk.rst

+Using the Raspberry Pi Pico SDK (PICO-SDK)
+==========================================
+
+A complete copy of the [Raspberry Pi Pico SDK](https://datasheets.raspberrypi.org/pico/raspberry-pi-pico-c-sdk.pdf)
+is included with the Arduino core, and all functions in the core are available
+inside the standard link libraries.
+
+For simple programs wishing to call these functions, simply include the
+appropriate header as shown below
+
+.. code:: cpp
+
+        #include "pico/stdlib.h"
+        
+        void setup() {
+            const uint LED_PIN = 25;
+            gpio_init(LED_PIN);
+            gpio_set_dir(LED_PIN, GPIO_OUT);
+            while (true) {
+                gpio_put(LED_PIN, 1);
+                sleep_ms(250);
+                gpio_put(LED_PIN, 0);
+                sleep_ms(250);
+            }
+        }
+        void loop() {}
+
+**Note:**  When you call SDK functions in your own app, the core and
+libraries are not aware of any changes to the Pico you perform.  So,
+you may break the functionality of certain libraries in doing so.
+
+**Warning:**  While you may spawn multicore applications on CORE1
+using the SDK, the Arduino core may have issues running properly with
+them.  In particular, anything involving flash writes (i.e. EEPROM,
+filesystems) will probably crash due to CORE1 attempting to read from
+flash while CORE0 is writing to it.

docs/serial.rst

+Serial Ports (USB and UART)
+===========================
+
+The Arduino-Pico core implements a software-based Serial-over-USB port
+using the USB ACM-CDC model to support a wide variety of operating
+systems.
+
+`Serial` is the USB serial port, and while `Serial.begin()` doea allow
+specifying a baud rate, this rate is ignored since it is USB-based.
+(Also be aware that this USB `Serial` port is responsible for resetting
+the RP2040 during the upload process, following the Arduino standard
+of 1200bps = reset to bootloader).
+
+The RP2040 provides two hardware-based UARTS with configurable
+pin selection.
+
+`Serial1` is UART0, and `Serial2` is UART1.
+
+Configure their pins using the `setXXX` calls prior to calling `begin()`
+.. code:: cpp
+
+        Serial1.setRX(pin);
+        Serial1.setTX(pin);
+        Serial1.begin(baud);
+
+For detailed information about the Serial ports, see the
+Arduino [Serial reference](https://www.arduino.cc/reference/en/language/functions/communication/serial/)

docs/servo.rst

+Servo Library
+=============
+
+A hardware-based servo controller is provided using the `Servo` library.
+It utilizes the PIO state machines and generates the appropriate servo
+control pulses, glitch-free and jitter-free (within crystal limits).
+
+Up to 8 Servos can be controlled in parallel assuming no other tasks
+require the use of a PIO machine.
+
+See the Arduino standard [Servo documentation](https://www.arduino.cc/reference/en/libraries/servo/)
+for detailed usage instructions.  There is also an included `sweep` example.

docs/spi.rst

+SPI (Serial Peripheral Interface)
+=================================
+
+The RP2040 has two hardware SPI interfaces, `spi0 (SPI)` and `spi1 (SPI1)`.
+These interfaces are supported by the `SPI` library in master mode.
+
+SPI pinouts can be set **before SPI.begin()** using the following calls:
+
+.. code:: cpp
+
+    bool setRX(pin_size_t pin);
+    bool setCS(pin_size_t pin);
+    bool setSCK(pin_size_t pin);
+    bool setTX(pin_size_t pin);
+
+Note that the `CS` pin can be hardware or software controlled by the sketch.
+When software controlled, the `setCS()` call is ignored.
+
+The [Arduino SPI documention](https://www.arduino.cc/en/reference/SPI) gives
+a detailed overview of the library, except for the following RP2040-specific
+changes:
+* `SPI.begin(bool hwCS)` can take an options `hwCS` parameter.
+By passing in `true` for `hwCS` the sketch does not need to worry about
+asserting and deasserting the `CS` pin between transactions.  The default
+is `false` and requires the sketch to handle the CS pin itself, as is the
+standard way in Arduino.
+* The interrupt calls (`usingInterrupt`, `notUsingInterrupt`,
+`attachInterrupt`, and `detachInterrpt`) are not implemented.

docs/wire.rst

+Wire (I2C Master and Slave)
+===========================
+
+The RP2040 has two I2C devices, `i2c0 (Wire)` and `i2c1 (Wire1)`
+
+The current implementation is compatible with the Arduino standard
+with the addition of two calls to allof the `SDA` and `SCL` pins
+to be set **before calling Wire.begin()**
+
+.. code:: cpp
+
+        bool setSDA(pin_size_t sda);
+        bool setSCL(pin_size_t scl);
+
+Both master and slave operation is supported.
+
+Master transmissions are buffered (up to 128 bytes) and only performed
+on `endTransmission`, as is standard with modern Arduino Wire implementations.
+
+For more detailed information, check the [Arduino Wire documentation.](https://www.arduino.cc/en/reference/wire)

libraries/I2S/src/I2S.cpp

@@ -27,9 +27,25 @@ I2SClass::I2SClass() {
     _curBuff = nullptr;
     _bps = 0;
     _writtenHalf = false;
+    _pinBCLK = 26;
+    _pinDOUT = 28;
 }
 
-bool I2SClass::begin(long sampleRate, pin_size_t sck, pin_size_t data) {
+bool I2SClass::setBCLK(pin_size_t pin) {
+    if (_running || (pin < 0) || (pin > 28)) {
+        return false;
+    }
+    _pinBCLK = pin;
+}
+
+bool I2SClass::setDOUT(pin_size_t pin) {
+    if (_running || (pin < 0) || (pin > 29)) {
+        return false;
+    }
+    _pinDOUT = pin;
+}
+
+bool I2SClass::begin(long sampleRate) {
     if (_running) {
         return false;
     }
@@ -48,8 +64,8 @@ bool I2SClass::begin(long sampleRate, pin_size_t sck, pin_size_t data) {
     }
 
     bzero(&_config, sizeof(_config));
-    _config.data_pin = data;
-    _config.clock_pin_base = sck;
+    _config.data_pin = _pinDOUT;
+    _config.clock_pin_base = _pinBCLK;
     _config.dma_channel = 0;
     _config.pio_sm = 1;
 

libraries/I2S/src/I2S.h

@@ -29,7 +29,9 @@ public:
   I2SClass();
 
   // Only 16 bitsPerSample are allowed by the PIO code.  Only write, no read.
-  bool begin(long sampleRate, pin_size_t sck = 26, /* lrclk is sck+1 */ pin_size_t data = 28);
+  bool setBCLK(pin_size_t pin);
+  bool setDOUT(pin_size_t pin);
+  bool begin(long sampleRate);
   void end();
 
   // from Stream
@@ -60,6 +62,8 @@ public:
   //void onReceive(void(*)(void)); -- no I2S input yet
 
 private:
+    pin_size_t _pinBCLK;
+    pin_size_t _pinDOUT;
     int _bps;
     int _freq;
     bool _running;