.. GPIO Zero: a library for controlling the Raspberry Pi's GPIO pins
..
.. Copyright (c) 2018-2021 Ben Nuttall <ben@bennuttall.com>
.. Copyright (c) 2019 Dave Jones <dave@waveform.org.uk>
..
.. SPDX-License-Identifier: BSD-3-Clause

===============
Pi Zero USB OTG
===============

The `Raspberry Pi Zero`_ and `Pi Zero W`_ feature a USB OTG port, allowing
users to configure the device as (amongst other things) an Ethernet device. In
this mode, it is possible to control the Pi Zero's GPIO pins over USB from
another computer using the :doc:`remote GPIO <remote_gpio>` feature.


GPIO expander method - no SD card required
==========================================

The GPIO expander method allows you to boot the Pi Zero over USB from the PC,
without an SD card. Your PC sends the required boot firmware to the Pi over the
USB cable, launching a mini version of Raspberry Pi OS and booting it in RAM.
The OS then starts the pigpio daemon, allowing "remote" access over the USB
cable.

At the time of writing, this is only possible using either the Raspberry Pi
Desktop x86 OS, or Ubuntu (or a derivative), or from another Raspberry Pi.
Usage from Windows and Mac OS is not supported at present.

Raspberry Pi Desktop x86 setup
------------------------------

1. Download an ISO of the `Raspberry Pi Desktop OS`_ from raspberrypi.org

2. Write the image to a USB stick or burn to a DVD.

3. Live boot your PC or Mac into the OS (select "Run with persistence" and your
   computer will be back to normal afterwards).

Raspberry Pi setup (using Raspberry Pi OS)
------------------------------------------

1. Update your package list and install the ``usbbootgui`` package:

.. code-block:: console

    $ sudo apt update
    $ sudo apt install usbbootgui

Ubuntu setup
------------

1. Add the Raspberry Pi PPA to your system:

.. code-block:: console

    $ sudo add-apt-repository ppa:rpi-distro/ppa

2. If you have previously installed ``gpiozero`` or ``pigpio`` with pip,
uninstall these first:

.. code-block:: console

    $ sudo pip3 uninstall gpiozero pigpio

3. Install the required packages from the PPA:

.. code-block:: console

    $ sudo apt install usbbootgui pigpio python3-gpiozero python3-pigpio

Access the GPIOs
----------------

Once your PC or Pi has the USB Boot GUI tool installed, connecting a Pi Zero
will automatically launch a prompt to select a role for the device. Select
"GPIO expansion board" and continue:

.. image:: images/gpio-expansion-prompt.png
    :align: center
    :width: 364px

It will take 30 seconds or so to flash it, then the dialogue will disappear.

Raspberry Pi OS will name your Pi Zero connection ``usb0``. On Ubuntu, this will
likely be something else. You can ping it using the address ``fe80::1%``
followed by the connection string. You can look this up using ``ifconfig``.

Set the :envvar:`GPIOZERO_PIN_FACTORY` and :envvar:`PIGPIO_ADDR` environment
variables on your PC so GPIO Zero connects to the "remote" Pi Zero:

.. code-block:: console

    $ export GPIOZERO_PIN_FACTORY=pigpio
    $ export PIGPIO_ADDR=fe80::1%usb0

Now any GPIO Zero code you run on the PC will use the GPIOs of the attached Pi
Zero:

.. image:: images/gpio-expansion-example.png
    :align: center
    :width: 640px

Alternatively, you can set the pin factory in-line, as explained in
:doc:`remote_gpio`.

Read more on the GPIO expander in blog posts on `raspberrypi.org`_ and
`bennuttall.com`_.

Legacy method - SD card required
================================

The legacy method requires the Pi Zero to have an SD card with Raspberry Pi OS
inserted.

Start by creating a Raspberry Pi OS (desktop or lite) SD card, and then
configure the boot partition like so:

1. Edit :file:`config.txt` and add ``dtoverlay=dwc2`` on a new line, then save
   the file.

2. Create an empty file called :file:`ssh` (no file extension) and save it in
   the boot partition.

3. Edit :file:`cmdline.txt`` and insert ``modules-load=dwc2,g_ether`` after
   ``rootwait``.

(See guides on `blog.gbaman.info`_ and `learn.adafruit.com`_ for more detailed
instructions)

Then connect the Pi Zero to your computer using a micro USB cable (connecting
it to the USB port, not the power port). You'll see the indicator LED flashing
as the Pi Zero boots. When it's ready, you will be able to ping and SSH into it
using the hostname ``raspberrypi.local``. SSH into the Pi Zero, install pigpio
and run the pigpio daemon.

Then, drop out of the SSH session and you can run Python code on your computer
to control devices attached to the Pi Zero, referencing it by its hostname (or
IP address if you know it), for example:

.. code-block:: console

    $ GPIOZERO_PIN_FACTORY=pigpio PIGPIO_ADDR=raspberrypi.local python3 led.py


.. _Raspberry Pi Zero: https://www.raspberrypi.org/products/raspberry-pi-zero/
.. _Pi Zero W: https://www.raspberrypi.org/products/raspberry-pi-zero-w/
.. _Raspberry Pi Desktop OS: https://www.raspberrypi.org/downloads/raspberry-pi-desktop/
.. _raspberrypi.org: https://www.raspberrypi.org/blog/gpio-expander/
.. _bennuttall.com: http://bennuttall.com/raspberry-pi-zero-gpio-expander/
.. _blog.gbaman.info: http://blog.gbaman.info/?p=791
.. _learn.adafruit.com: https://learn.adafruit.com/turning-your-raspberry-pi-zero-into-a-usb-gadget/ethernet-gadget
