/*! \page page_usrp_e3x0 USRP-E3x0 Series

\tableofcontents

\section e3x0_feature_list Comparative features list - E310

- Hardware Capabilities:
	  Integrated RF frontend (70 MHz - 6 GHz)
	- External PPS reference input
	- Configurable clock rate
	- Internal GPIO connector with UHD API control
	- 2 USB 2.0 Host ports
	- Internal GPS
	- Soundcard mono input / stereo output
	- USB UART
	- Internal IMU
	- Zynq-7020 FPGA
- FPGA Capabilities:
        - 2 RX DDC chains in FPGA
        - 2 TX DUC chain in FPGA
	- Timed commands in FPGA
	- Timed sampling in FPGA
	- 16-bit fixed point sample mode (sc16)
	- Up to 10 MHz of RF bandwidth with 16-bit samples

\section e3x0_getting_started Getting started

This will run you through the first steps relevant to get your USRP E310
up and running.

\subsection e3x0_first_boot First boot

There are two different methods to connect to the device

- using the onboard serial to usb connector
- using the gigabit ethernet connector and a ssh client on your host computer

For the first boot, booting with the serial cable connected to the device
is recommended, as it allows to review and modify the network configuration,
and allows to enter the bootloader in case of issues during the boot.


\subsubsection e3x0_first_boot_serial Serial connection

To use the serial connection together with a Linux or OSX machine (most other UNIX variants come with a version of screen, too)
a terminal emulator such as screen can be used:

    $ sudo screen /dev/ttyUSB0 115200

The exact device node /dev/ttyUSB0 depends on your operating system's driver and other USB devices that might be already connected.
It can be usually found by perusing the output of dmesg or journalctl, after connecting the USRP E310 device to your host computer.

An example of a dmesg output for the serial to usb converter:

    924.102764] usb 1-1: FTDI USB Serial Device converter now attached to ttyUSB0


On Microsoft Windows the serial connection can be established using a tool such as Putty by selecting a baudrate of 115200 and the corresponding serial port for the serial to usb converter.

In both cases you should see boot messages fly by and finally end up with a login prompt similar to the following:

    ettus-e300 login:

Note: The username is 'root' and the default password is empty.

You should be presented with a shell similar to the following

    root@ettus-e300:~#


\subsubsection e3x0_first_boot_ssh SSH connection

The USRP E310 device relies on the DHCP protocol to automatically obtain an IP address.
In case your network setup does not include a DHCP server, refer to the section \ref e3x0_first_boot_serial or configure a DHCP server to hand out IP addresses on your network.

After the device obtained an IP address you can log in from a Linux or OSX machine by typing:

    $ ssh root@192.168.10.42

where the IP address depends on your local network setup.

On Microsoft Windows again the connection can be established using a tool such as Putty, by selecting a username of root without password.

You should be presented with a shell similar to the following

    root@ettus-e300:~#

\section e3x0_sdk Using the SDK

In order to facilitate software development for the integrated ARM Cortex-A9 processor, a <a href="http://www.yoctoproject.org">Yocto Project</a> based SDK is provided in the download section of our website.
This SDK contains a cross-compiler, a cross-linker as well as a cross-debugger and can be used to develop your user space applications for the Ettus USRP-E310 devices.


\subsection e3x0_sdk_installation Installation
The following section will guide you through the installation of the provided SDK on a Linux development machine.

\subsubsection e3x0_sdk_installation_download Obtaining the correct SDK
It is necessary for the SDK version and the image version to match, to ensure the versions of the software installed on the device and the version of the software the SDK will build against match.

If you are not sure which image is installed on your device, upgrading to the latest stable version is recommended. See the appropriate section for details on upgrading.

\subsubsection e3x0_sdk_installation_install Obtaining the right toolchain

To install the toolchain you downloaded type:

    $ ./oecore-${TCLIBC}-${SDK_ARCH}-${IMAGE_BASENAME}-${TUNE_PKGARCH}.sh

This will prompt you for an installation path.
Please ensure you have sufficient disk space, as each of the SDKs may require several gigabytes of disk space (depends on the image flavor selected).

This will allow you to compile UHD as well as (depending on the image flavor) other software.

Please note, that while several toolchains can be installed in parallel, they have to be installed to different directories.

\subsection e3x0_sdk_usage Usage

Having installed the toolchain in the last step,
in order to build software for your device open a new shell and type:

    $ . <yoursdkinstallpath>/environment-setup-armv7ahf-vfp-neon-oe-linux-gnueabi

This will modifiy the PATH, CC, CXX etc, environment variables and allow you to compile software for your USRP E310 device.
To verify all went well you can try:

    $ $CC -dumpmachine

which should return 'arm-oe-linux-gnueabi'.

\subsubsection e3x0_sdk_usage_uhd Building UHD

-# Obtain the UHD source code via git or tarball
-# Setup your environment as described in \ref e3x0_sdk_usage
-# Type the following in the build directory (assuming a build in host/build):

        $ cmake -DCMAKE_TOOLCHAIN_FILE=<youruhdsrc>/host/cmake/Toolchains/oe-sdk_cross.cmake -DCMAKE_INSTALL_PREFIX=/usr -DENABLE_E300=ON ..
        $ make

\subsubsection e3x0_sdk_usage_gnuradio Building GNU Radio

-# Obtain the gnuradio source code via git.
-# Setup the environment as described in \ref e3x0_sdk_usage
-# Use the following commands to create a build directory, configure and compile gnuradio. You only need create the build directory once.

\code{.sh}
$ mkdir build-arm
$ cmake -Wno-dev -DCMAKE_TOOLCHAIN_FILE=../cmake/Toolchains/oe-sdk_cross.cmake \-DCMAKE_INSTALL_PREFIX=/usr -DENABLE_GR_VOCODER=OFF -DENABLE_GR_ATSC=OFF \
-DENABLE_GR_DTV=OFF -DENABLE_DOXYGEN=OFF ../
\endcode

Several GNU Radio components depend on running binaries built for the build
machine during compile. These binaries can be built and used for cross
compiling, but this is an advanced topic.

\section e3x0_image_building Rebuilding the file system

The file system images are built using OpenEmbedded Core. The `repo` tool is
used to manage the versions of the various layers that supply recipes for
building the image. For more documentation see http://www.yoctoproject.org.
These notes will show you how to rebuild the files used to create the SD
card included with the E310. These instructions assume you ahve a working
knowledge of Linux.

-# Install `repo`.
\code{.sh}
 $ curl http://commondatastorage.googleapis.com/git-repo-downloads/repo > repo
 $ chmod a+x repo
 $ sudo mv repo /usr/local/bin
\endcode

-# Configure the repo manifest that controls the build.
\code{.sh}
 $ mkdir e300-oe-build
 $ cd e300-oe-build
 $ repo init -u git://github.com/EttusResearch/e300-manifest.git -b release1
\endcode

-# Initialize the environment. This will take a little while.
\code{.sh}
 $ repo sync
 $ TEMPLATECONF=`pwd`/meta-ettus/conf source ./oe-core/oe-init-build-env ./build ./bitbake
\endcode

At this point you should review the file in conf/local.conf and make sure
path names make sense for your machine.

-# Build an image. This will take a few hours, especially the first run since
it will download all the required sources. (These are saved locally for future
builds)
\code{.sh}
 $ export MACHINE="ettus-e300"
 $ bitbake gnuradio-dev-image
\endcode

When this completes, the files needed to create the sd card are in
`tmp-glibc/deploy/images/ettus-e300`

-# Build the toolchain.
\code{.sh}
 $ bitbake -c populate_sdk gnuradio-dev-image
\endcode

The sdk is in `tmp-glibc/deploy/sdk`

Note that you can set the `MACHINE` variable in `local.conf so that you no
longer need to set it from the command line.

When you log back in, you will need to setup the OpenEmbedded environment
again by:

\code{.sh}
 $ cd e300-oe-build/oe-core
 $ . oe-core/oe-init-build-env ./build ./bitbake
\endcode

\section e3x0_load_fpga_imgs Specifying a Non-standard FPGA Image

\subsection e3x0_load_fpga_imgs_uhd Using UHD to load FPGA images

UHD software will automatically select the USRP E310 images from the
installed images package. The image selection can be overridden with the
`fpga` device address parameter.

Example device address string representations to specify non-standard
image:

    $ uhd_usrp_probe --args='fpga=usrp_e310_fpga.bit'

\subsection e3x0_load_fpga_imgs_jtag Using JTAG to load FPGA images

The USRP-E Series device features an on-board JTAG connector (see \ref e3x0_hw_chipscope) that can be accessed on the PCB
of the device. The iMPACT tool in the <a href="http://www.xilinx.com/support/download/index.htm">Xilinx Programming Tools (ISE, iMPACT)</a> package can be used to load an image over the JTAG interface.

If you have iMPACT installed, you can use the `impact_jtag_programmer.sh` tool to install images. Make sure your e3x0 is powered on and connected to your computer using the internal JTAG connector. Then run the tool:

    <path_to_uhd_tools>/impact_jtag_programmer.sh --fpga-path=<fpga_image_path>

\subsection e3x0_setup_change_ip Change the USRP's IP address

You may need to change the USRP's IP address for several reasons:
- to satisfy your particular network configuration
- to use multiple USRP-E Series devices with the same host computer
- to set a known IP address into USRP (in case you forgot)




\section e3x0_hw Hardware Notes

\subsection e3x0_hw_fpanel Front Panel

\image html e3x0_fp_overlay.png "USRP E310 Front panel"

- **RF A Group**
  + **TX/RX LED**: Indicates that data is streaming on the TX/RX channel on frontend side A
  + **RX2 LED**: Indicates that data is streaming on the RX2 channel on frontend side A

- **RF B Group**
  + **TX/RX LED**: Indicates that data is streaming on the TX/RX channel on frontend B
  + **RX2 LED**: Indicates that data is streaming on the RX2 channel on frontend B
- **PWR**: Power switch

- **SYNC**: Input port for external PPS signal

- **GPS**: Connection for the GPS antenna

- **AUDIO**: Audio input / output

\subsection e3x0_hw_rear_panel Rear Panel

\image html e3x0_rp_overlay.png "USRP E310 Rear Panel"

- **PWR**: Locking connector for the USRP-E Series power supply
- **1G ETH**: RJ45 port for Ethernet interfaces
- **USB**: USB 2.0 Port
- **SERIAL**: Micro USB connection for serial uart console

\subsection e3x0_hw_sync Clock and Time Synchronization
Unlike most USRP devices, the E310 does not have independent reference clock and time source inputs.
It is possible, however, to discipline the internal reference clock using an external time (PPS) source
connected to the SYNC input pin. The E310 FPGA has a subsystem that can use the PPS signal from the
SYNC pin or the internal GPS to align edges of the reference clock to edges of a shared PPS signal. 
This alignment happens automatically when the time source in UHD is set to "gpsdo" or "external". 
Please note that because the SYNC input can only accept a PPS signal, the only supported value for 
the reference clock source is "internal".


\subsection e3x0_hw_pps PPS - Pulse Per Second
Using a PPS signal for timestamp synchronization requires a LVCMOS or a 5V logic input signal.
An external PPS can be used to discipline the internal reference clock. This feature is automatically 
enabled with the time source is set to "external".

To test the PPS input, you can use the following tool from the UHD examples:

- `<args>` are device address arguments (optional if only one USRP device is on your machine)

    cd <install-path>/lib/uhd/examples
    ./test_pps_input --args=\<args\>

\subsection e3x0_hw_gps Internal GPS

Your USRP-E Series device comes with an internal GPS.
In order to get a lock on a satellite an external GPS antenna is required.
The PPS from the internal GPS can be used to discipline the internal reference clock. This feature is automatically 
enabled with the time source is set to "gpsdo".

The device provides a 3.3V supply voltage to an external antenna connected to the *GPS* port
of your device. Note that this supply voltage is turned off in order to safe power upon destruction of the software object.

\subsection e3x0_hw_imu Inertial Measurement Unit (IMU)

Your USRP-E Series device has an onboard IMU that provides
9 axis (Gyro, Accelerometer and compass) functionality.

The USRP-E Series images ship with several example applications based on
<a href="https://github.com/richards-tech/RTIMULib">RTIMULib</a> that allow the user
to explore the basic functionality of the IMU as well as to calibrate it.

To test the accelerometer, run:

    $ RTIMULibDrive

This will print the current acclerometer values on the console.

To launch the IMU calibration procedure, run:

    $ RTIMULibCal

and follow the onscreen instructions. Please note that magnetometer calibration is important to obtain
sensible results if the IMU is to be used in sensor fusion applications.

Using X11 forwarding over SSH (see \ref e3x0_faq) a complete sensor fusion application can be run over SSH
from a host computer by typing:

    $ RTIMULibDemo

This should open a graphical window on the host computer that displays the various outputs of the IMU,
as well as quaternion measurements based on different sensor fusion algorithms.

\image html e3x0_imu_demo.png "RTIMULibDemo"

For more advanced IMU based applications please refer to the <a href="https://github.com/richards-tech/RTIMULib">RTIMULib repository</a> as well as the datasheets.

\subsection e3x0_hw_gpio Internal GPIO

### Connector

\image html e3x0_gpio_conn.png "E3x0 GPIO Connector"

### Pin Mapping

- Pin 1:   +3.3V
- Pin 2:   Reserved
- Pin 3:   Data[5]
- Pin 4:   Reserved
- Pin 5:   Data[4]
- Pin 6:   Data[0]
- Pin 7:   Data[3]
- Pin 8:   Data[1]
- Pin 9:   0V
- Pin 10:  Data[2]

Please see the \ref page_gpio_api for information on configuring and using the GPIO bus.

\subsection e3x0_hw_audio Audio connectors
The E3x0 2.5 mm Audio Jack TRRS pins are assigned as follows: Tip=Mic, Ring1=Right, Ring2=Left, Sleeve=GND. 

\image html TRRS.png "Audio Jack"

The Left/Right audio outputs are compatible with typical low-impedance headphones (16 to 32 Ohms). The Microphone pin provides approximately 2 mA bias at 2.2 V when not suspended. A variety of pin configurations can be found on commonly available headsets, so an adapter may be required.

\subsection e3x0_hw_chipscope Debugging custom FPGA designs with Xilinx Chipscope

### Connector

\image html e3x0_jtag_conn.png "E3x0 JTAG Connector"

### Pin Mapping

- Pin 1: TDO
- Pin 2: 3.3V
- Pin 3: TCK
- Pin 4: TDI
- Pin 5: 0V
- Pin 6: TMS


Xilinx chipscope allows for debugging custom FPGA designs similar to a logic analyzer.
USRP-E series devices can be used with Xilinx chipscope using the internal JTAG connector.

Further information on how to use Chipscope can be found in the *Xilinx Chipscope Pro Software and Cores User Guide (UG029)*.

\section e3x0_dboards Daughterboard notes

\subsection e3x0_dboard_e310 E310 MIMO XCVR board

The USRP E310 MIMO XCVR daughterboard features an integrated MIMO capable RF frontend.

\subsubsection e3x0_dboard_e310_tuning Frontend tuning

The RF frontend has individually tunable receive and transmit chains.
Both transmit and receive can be used in a MIMO configuration. For
the MIMO case, both receive frontends share the RX LO, and both transmit
frontends share the TX LO. Each LO is tunable between 50 MHz and 6 GHz.

\subsubsection e3x0_dboard_e310_gain Frontend gain

All frontends have individual analog gain controls. The receive
frontends have 73 dB of available gain; and the transmit frontends have
89.5 dB of available gain. Gain settings are application specific, but
it is recommended that users consider using at least half of the
available gain to get reasonable dynamic range.

\subsubsection e3x0_dboard_e310_pll Frontend LO lock status

The frontends provide a *lo-locked* sensor that can be queried through the UHD API.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
// assumes 'usrp' is a valid uhd::usrp::multi_usrp::sptr instance

// get status for rx frontend
usrp->get_rx_sensor("lo-locked");

// get status for tx frontend
usrp->get_tx_sensor("lo-locked");
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

\subsubsection e3x0_dboard_e310_band_select Frontend Filter and Antenna Switches

The transmit and receive filter banks uses switches to select between the available filters. These paths are
also dependent on the antenna switch settings. Incorrectly setting the switches generally results
in attenuated input / output power. Receive filters are band pass (series high & low pass filters), 
transmit filters are low pass.

Source code related to controlling the filter band and antenna switches resides in e300_impl.c. Specifically, refer to methods 
`e300_impl::_update_bandsel`, `e300_impl::_update_atrs`, `e300_impl::_update_gpio`, and `e300_impl::_update_enables`. Generally, these 
methods set the switches depending on the state of transmit and receive streams.

The following sections provide switch setting tables for antenna and filter selection for frontends A & B receive and transmit paths.
For futher details refer to the schematics. 

\subsubsection e3x0_dboard_e310_frontend_a_switches Frontend Side A Filter and Antenna Switches

_Note: X = don't care, T = If full duplex, set bits according to transmit table, otherwise don't care.
Filter range A – B will be selected if A <= freq < B._

__Receive__
RX Port | RX Filter (MHz) | VCTXRX2_V1,V2 | VCRX2_V1,V2 | RX2_BANDSEL[2:0] | RX2B_BANDSEL[1:0] | RX2C_BANDSEL[1:0]
:-----: | :-------------: | :-----------: | :---------: | :--------------: | :---------------: | :---------------:
TRX-A   | < 450           | 01            | 10          | 101              | XX                | 01               
TRX-A   | 450 – 700       | 01            | 10          | 011              | XX                | 11               
TRX-A   | 700 – 1200      | 01            | 10          | 001              | XX                | 10               
TRX-A   | 1200 – 1800     | 01            | 10          | 000              | 01                | XX               
TRX-A   | 1800 – 2350     | 01            | 10          | 010              | 11                | XX               
TRX-A   | 2350 – 2600     | 01            | 10          | 100              | 10                | XX               
TRX-A   | 2600 – 6000     | 01            | 01          | XXX              | XX                | XX               
RX2-A   | 70  – 450       | TT            | 01          | 101              | XX                | 01               
RX2-A   | 450 – 700       | TT            | 01          | 011              | XX                | 11               
RX2-A   | 700 – 1200      | TT            | 01          | 001              | XX                | 10               
RX2-A   | 1200 – 1800     | TT            | 01          | 000              | 01                | XX               
RX2-A   | 1800 – 2350     | TT            | 01          | 010              | 11                | XX               
RX2-A   | 2350 – 2600     | TT            | 01          | 100              | 10                | XX               
RX2-A   | >= 2600         | TT            | 10          | XXX              | XX                | XX               

__Transmit__
TX Port | TX Filter (MHz) | VCTXRX2_V1,V2 | TX_ENABLE2A,2B | TX_BANDSEL[2:0]
:-----: | :-------------: | :-----------: | :------------: | :-------------:
TRX-A   | < 117.7         | 10            | 01             | 111            
TRX-A   | 117.7 – 178.2   | 10            | 01             | 110            
TRX-A   | 178.2 – 284.3   | 10            | 01             | 101            
TRX-A   | 284.3 – 453.7   | 10            | 01             | 100            
TRX-A   | 453.7 – 723.8   | 10            | 01             | 011            
TRX-A   | 723.8 – 1154.9  | 10            | 01             | 010            
TRX-A   | 1154.9 – 1842.6 | 10            | 01             | 001            
TRX-A   | 1842.6 – 2940.0 | 10            | 01             | 000            
TRX-A   | >= 2940.0       | 11            | 10             | XXX            
_Note: Although the transmit filters are low pass, this table describes UHD's tuning range for selecting each filter path.
The table also includes the required transmit enable state._

\subsubsection e3x0_dboard_e310_frontend_b_switches Frontend Side B Filter and Antenna Switches

_Note: X = don't care, T = If full duplex, set bits according to transmit table, otherwise don't care.
Filter range A – B will be selected if A <= freq < B._

__Receive__
RX Port | RX Filter (MHz) | VCTXRX1_V1,V2 | VCRX1_V1,V2 | RX1_BANDSEL[2:0] | RX1B_BANDSEL[1:0] | RX1C_BANDSEL[1:0]
:-----: | :-------------: | :-----------: | :---------: | :--------------: | :---------------: | :---------------:
TRX-B   | < 450           | 10            | 01          | 100              | XX                | 10               
TRX-B   | 450 – 700       | 10            | 01          | 010              | XX                | 11               
TRX-B   | 700 – 1200      | 10            | 01          | 000              | XX                | 01               
TRX-B   | 1200 – 1800     | 10            | 01          | 001              | 10                | XX               
TRX-B   | 1800 – 2350     | 10            | 01          | 011              | 11                | XX               
TRX-B   | 2350 – 2600     | 10            | 01          | 101              | 01                | XX               
TRX-B   | 2600 – 6000     | 10            | 10          | XXX              | XX                | XX               
RX2-B   | 70  – 450       | TT            | 10          | 100              | XX                | 10               
RX2-B   | 450 – 700       | TT            | 10          | 010              | XX                | 11               
RX2-B   | 700 – 1200      | TT            | 10          | 000              | XX                | 01               
RX2-B   | 1200 – 1800     | TT            | 10          | 001              | 10                | XX               
RX2-B   | 1800 – 2350     | TT            | 10          | 011              | 11                | XX               
RX2-B   | 2350 – 2600     | TT            | 10          | 101              | 01                | XX               
RX2-B   | >= 2600         | TT            | 01          | XXX              | XX                | XX               

__Transmit__
TX Port | TX Filter (MHz) | VCTXRX1_V1,V2 | TX_ENABLE1A,1B | TX1_BANDSEL[2:0]
:-----: | :-------------: | :-----------: | :------------: | :--------------:
TRX-B   | < 117.7         | 00            | 01             | 111             
TRX-B   | 117.7 – 178.2   | 00            | 01             | 110             
TRX-B   | 178.2 – 284.3   | 00            | 01             | 101             
TRX-B   | 284.3 – 453.7   | 00            | 01             | 100             
TRX-B   | 453.7 – 723.8   | 00            | 01             | 011             
TRX-B   | 723.8 – 1154.9  | 00            | 01             | 010             
TRX-B   | 1154.9 – 1842.6 | 00            | 01             | 001             
TRX-B   | 1842.6 – 2940.0 | 00            | 01             | 000             
TRX-B   | >= 2940.0       | 11            | 10             | XXX             
_Note: Although the transmit filters are low pass, the following table describes UHD's tuning range for selecting each filter path.
The table also includes the required transmit enable states._

\section e3x0_misc Miscellaneous

\subsection e3x0_misc_multirx Multiple RX channels

There are two complete DDC and DUC DSP chains in the FPGA. In the single channel case,
only one chain is ever used. To receive / transmit from both channels, the user must set the **RX** or **TX**
subdevice specification.

In the following example, a E310 MIMO XCVR is installed.
Channel 0 is sourced from subdevice **A**,
and channel 1 is sourced from subdevice **B**

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
// assumes 'usrp' is a valid uhd::usrp::multi_usrp::sptr instance

usrp->set_rx_subdev_spec("A:A A:B");
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

\subsection e3x0_misc_sensors Available Sensors

The following sensors are available for the USRP-E Series motherboards;
they can be queried through the API.

- **fe_locked** - rx / tx frontend pll locked
- **temp** - processor temperature value
- **gps_time** and **gps_locked** sensors are added when the GPS is found

\subsection e3x0_network_mode Network Mode

Your USRP-E series device can be used in network mode for narrow band signal observation, evaluation and debugging purposes.

Please note that when compared with normal operation as a standalone device the usable bandwidth is limited and therefore Network Mode is not the recommended mode of operation.

In order to use the device in network mode it is necessary to start the *usrp_e3x0_network_mode* executable on the device.
In order to start the executable please log into your device either via SSH or serial console(see \ref e3x0_first_boot) and type

    $ usrp_e3x0_network_mode

Your device should now be discoverable by your host computer via the usual UHD tools. If you are having trouble communicating with your device see the \ref e3x0_comm_problems section.

\subsubsection e3x0_addressing Addressing the Device

### Single device configuration

In a single-device configuration,
the USRP device must have a unique IPv4 address on the host computer.
The USRP can be identified through its IPv4 address or resolvable hostname.
See the application notes on \ref page_identification.
Use this addressing scheme with the uhd::usrp::multi_usrp interface (not a typo!).

Example device address string representation for a USRP-E Series device with IPv4 address 192.168.10.2:

    addr=192.168.10.2

### Multiple device configuration

In a multi-device configuration,
each USRP device must have a unique IPv4 address on the host computer.
The device address parameter keys must be suffixed with the device index.
Each parameter key should be of the format \<key\>\<index\>.
Use this addressing scheme with the uhd::usrp::multi_usrp interface.

- The order in which devices are indexed corresponds to the indexing of the transmit and receive channels.
- The key indexing provides the same granularity of device identification as in the single device case.

Example device address string representation for 2 USRPs with IPv4 addresses **192.168.10.2** and **192.168.20.2**:

    addr0=192.168.10.2, addr1=192.168.20.2

\section e3x0_comm_problems Communication Problems

When setting up a development machine for the first time,
you may have various difficulties communicating with the USRP device.
The following tips are designed to help narrow down and diagnose the problem.

\subsection e3x0_comm_problems_runtimeerr RuntimeError: no control response

This is a common error that occurs when you have set the subnet of your network
interface to a different subnet than the network interface of the USRP device.  For
example, if your network interface is set to **192.168.20.1**, and the USRP device is **192.168.10.2**
(note the difference in the third numbers of the IP addresses), you
will likely see a 'no control response' error message.

Fixing this is simple - just set the your host PC's IP address to the same
subnet as that of your USRP device. Instructions for setting your IP address are in the
previous section of this documentation.

\subsection e3x0_comm_problems_firewall Firewall issues

When the IP address is not specified,
the device discovery broadcasts UDP packets from each Ethernet interface.
Many firewalls will block the replies to these broadcast packets.
If disabling your system's firewall
or specifying the IP address yields a discovered device,
then your firewall may be blocking replies to UDP broadcast packets.
If this is the case, we recommend that you disable the firewall
or create a rule to allow all incoming packets with UDP source port **49152**.

\subsection e3x0_comm_problems_ping Ping the device
The USRP device will reply to ICMP echo requests ("ping").
A successful ping response means that the device has booted properly
and that it is using the expected IP address.

    ping 192.168.10.2

\subsection e3x0_comm_problems_monitor Monitor the host network traffic
Use Wireshark to monitor packets sent to and received from the device.

\subsection e3x0_comm_problems_leds Observe Ethernet port LEDs
When there is network traffic arriving at the Ethernet port, LEDs will light up.
You can use this to make sure the network connection is correctly set up, e.g.
by pinging the USRP and making sure the LEDs start to blink.


\subsection e3x0_faq Frequently Asked Questions

 - Communication
  -# How do I enable X forwarding so I can run X apps on the E3x0?<br>
     In the file `/etc/ssh/sshd_config`, uncomment the line \#`X11Forwarding no`
     and change "no" to "yes".

\section e3x0_apps Applications

\subsection e3x0_apps_gsm GSM Base Station

OpenBTS allows the USRP E310 to serve as a GSM base station capable of providing voice and messaging services to standard GSM handsets. General information on the OpenBTS project can be found at the official webpage.

http://www.openbts.org

Special instructions to install OpenBTS on the E310 can be found on the OpenBTS wiki.

http://openbts.org/w/index.php/E3x0


*/
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