USB-Mux Overview
###################

Theory Of Operation
-------------------

USB paths inside the USB-Mux
~~~~~~~~~~~~~~~~~~~~~~~~~~~~

In this chapter :term:`DUT` describes the Embedded Device under Test.
The :term:`host` is the computer controlling the operation of the USB-Mux.
The :term:`device` is a USB device connected to the *device* port, eg. a
flash drive.

The USB-Mux contains a 3 port USB hub:

(1) The microcontroller inside the USB-Mux is connected to port 1.
(2) The :term:`DUT` can be multiplexed to port 2.
(3) The *device* can be multiplexed to port 3.

The USB-Mux can be instructed in software to create
the following conditions:

(1) Isolation of the :term:`DUT` and Device ports.
    This is the default mode after power on.

.. code-block:: none

                                          +-----------------------+
                                          | USB-Mux               |
                                       +--|                       |
                                       |  | SN:   00002           |
                                       |  | Path: 5-1.3.4.2.1     |
                                       |  +-----------------------+
            VCC: 4.99V    +---------+  |
     Host |>--------------|       1 |--+         ID: High
                          |         |           VCC: 0.00V
                          |       2 |----x    ------------|> DUT
                          |         |
                          |       3 |----x    ------------|> Device
                          +---------+           VCC: 0.00V

(2) A direct connection between the :term:`DUT`, in the
    USB Host role, to the Device port of the USB-Mux.

.. code-block:: none

                                         +-----------------------+
                                         | USB-Mux               |
                                      +--|                       |
                                      |  | SN:   00002           |
                                      |  | Path: 5-1.3.4.2.1     |
                                      |  +-----------------------+
           VCC: 4.99V    +---------+  |
    Host |>--------------|       1 |--+         ID: Low
                         |         |           VCC: 5.12V
                         |       2 |----x    +-----------|> DUT
                         |         |         |
                         |       3 |----x    +-----------|> Device
                         +---------+           VCC: 5.11V

(3) A connection via the USB-Hub integrated in the USB-Mux
    between the :term:`DUT`, in the USB Device role, and the test host.

.. code-block:: none

                                          +-----------------------+
                                          | USB-Mux               |
                                       +--|                       |
                                       |  | SN:   00002           |
                                       |  | Path: 5-1.3.4.2.1     |
                                       |  +-----------------------+
            VCC: 4.99V    +---------+  |
     Host |>--------------|       1 |--+         ID: High
                          |         |           VCC: 4.79V
                          |       2 |---------------------|> DUT
                          |         |
                          |       3 |----x    ------------|> Device
                          +---------+           VCC: 0.00V

(4) A connection via the USB-Hub integrated in the USB-Mux
    between the Device port and the host.

.. code-block:: none

                                          +-----------------------+
                                          | USB-Mux               |
                                       +--|                       |
                                       |  | SN:   00002           |
                                       |  | Path: 5-1.3.4.2.1     |
                                       |  +-----------------------+
            VCC: 4.99V    +---------+  |
     Host |>--------------|       1 |--+         ID: High
                          |         |           VCC: 0.15V
                          |       2 |----x    ------------|> DUT
                          |         |
                          |       3 |---------------------|> Device
                          +---------+           VCC: 4.79V

(5) Modes 3 and 4 can be combined to connect both :term:`DUT` and
    *device* to the host.

.. code-block:: none

                                         +-----------------------+
                                         | USB-Mux               |
                                      +--|                       |
                                      |  | SN:   00002           |
                                      |  | Path: 5-1.3.4.2.1     |
                                      |  +-----------------------+
           VCC: 4.99V    +---------+  |
    Host |>--------------|       1 |--+         ID: High
                         |         |           VCC: 4.80V
                         |       2 |---------------------|> DUT
                         |         |
                         |       3 |---------------------|> Device
                         +---------+           VCC: 4.80V


Switch sequence when multiplexing
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

When the USB-Mux switches between modes using the control software
the following steps are executed:

#. The currently active connection is electrically disconnected.
#. The control software waits 0.5s for the switches to settle and
   for the bus-members to notice a disconnect.
#. The new connection is made.
#. The new connection is discovered by the bus-members
   via USB hotplug logic.

Using the ID pin
~~~~~~~~~~~~~~~~

The USB-Mux has an ID pin output in the :term:`DUT` connection.
By default this pin is switched according to the connection made to the DUT.
This behavior can be disabled.

The ID pin is used to signal the following modes to a :term:`DUT`:

* When the ID pin is pulled low a OTG-capable DUT will go into the host mode.
* When the ID pin is floating (usually high) the DUT will go into device mode.

Hardware
--------

The following figure shows a rendering of the USB-Mux,
including the connectors and their associated case-printing:

.. figure:: product-operation-overview.svg.png

The connectors and their respective function are:

On the right side of the device:

- **Device:** USB port that can either be connected through to the :term:`DUT` or Host.
- **DUT:** USB signals on a Pin-Header to connect to the :term:`DUT` via
  appropriate cabling.
  Can be connected to the Device or Host port using the control software.

On the left side of the device:

- **Host:** USB-Port used to control the USB-Mux and optionally connect to
  either the :term:`DUT` or Device port.
- **DUT Power:** Lockout-Switch that, when activated, prevents direct connections
  between the Host and :term:`DUT`.