/*! \page page_usrp2 USRP2 and N2x0 Series

\tableofcontents

\section usrp2_features Comparative features list

- Hardware Capabilities:
    -   1 transceiver card slot
    -   External PPS reference input
    -   External 10 MHz reference input
    -   MIMO cable shared reference
    -   Fixed 100 MHz clock rate
    -   Internal GPSDO option (N2x0 only)
- FPGA Capabilities:
    -   2 RX DDC chains in FPGA
    -   1 TX DUC chain in FPGA
    -   Timed commands in FPGA (N2x0 only)
    -   Timed sampling in FPGA
    -   16-bit and 8-bit sample modes (sc8 and sc16)
        -   Up to 25 MHz of RF BW with 16-bit samples
        -   Up to 50 MHz of RF BW with 8-bit samples

\section usrp2_load Load the Images onto the SD card (USRP2 only)

<b>Warning!</b> Use `usrp2_card_burner` with caution. If you specify
the wrong device node, you could overwrite your hard drive. Make sure
that `--dev=` specifies the SD card.

<b>Warning!</b> It is possible to use 3rd party SD cards with the USRP2.
However, certain types of SD cards will not interface with the CPLD:

-   Cards can be SDHC, which is not a supported interface.
-   Cards can have unexpected timing characteristics.

For these reasons, we recommend that you use the SD card that was
supplied with the USRP2.

\subsection usrp2_load_cardburner Use the card burner tool (UNIX)

    sudo <install-path>/lib/uhd/utils/usrp2_card_burner_gui.py

    -- OR --

    cd <install-path>/lib/uhd/utils
    sudo ./usrp2_card_burner.py --dev=/dev/sd<XXX> --fpga=<path_to_fpga_image>
    sudo ./usrp2_card_burner.py --dev=/dev/sd<XXX> --fw=<path_to_firmware_image>

Use the `--list` option to get a list of possible raw devices. The
list result will filter out disk partitions and devices too large to be
the sd card. The list option has been implemented on Linux, Mac OS X,
and Windows.

\subsection usrp2_load_cardburnerwin Use the card burner tool (Windows)

    <path_to_python.exe> <install-path>/lib/uhd/utils/usrp2_card_burner_gui.py

\section usrp2_loadflash Load the Images onto the On-board Flash (USRP-N Series only)

The USRP-N Series can be reprogrammed over the network to update or
change the firmware and FPGA images. When updating images, always burn
both the FPGA and firmware images before power cycling. This ensures
that when the device reboots, it has a compatible set of images to boot
into.

\subsection usrp2_loadflash_netburner Use the net burner tool

Use default images:

    usrp_n2xx_simple_net_burner --addr=<IP address>

Use custom-built images:

    usrp_n2xx_simple_net_burner --addr=<IP address> --fw=<firmware path> --fpga=<FPGA path>

<b>Note:</b> Different hardware revisions require different FPGA images.
Determine the revision number from the sticker on the rear of the
chassis. Use this number to select the correct FPGA image for your
device.

For users who would prefer a graphical utility, a Python-based
alternative exists.

\subsection usrp2_loadflash_gui Use the graphical net burner tool (Linux)

    <install-path>/lib/uhd/utils/usrp_n2xx_net_burner_gui.py

\subsection usrp2_loadflash_guiwin Use the graphical net burner tool (Windows)

    <path_to_python.exe> <install-path>/lib/uhd/utils/usrp_n2xx_net_burner_gui.py

\subsection usrp2_loadflash_brick Device recovery and bricking

Its possible to put the device into an unusable state by loading bad
images. Fortunately, the USRP-N Series can be booted into a safe
(read-only) image. Once booted into the safe image, the user can once
again load images onto the device.

The safe-mode button is a pushbutton switch (S2) located inside the
enclosure. To boot into the safe image, hold-down the safe-mode button
while power-cycling the device. Continue to hold-down the button until
the front-panel LEDs blink and remain solid.

When in safe-mode, the USRP-N device will always have the IP address **192.168.10.2**.

\section usrp2_network Setup Networking

The USRP2 only supports Gigabit Ethernet and will not work with a 10/100
Mbps interface. However, a 10/100 Mbps interface can be connected
indirectly to a USRP2 through a Gigabit Ethernet switch.

\subsection usrp2_network_setuphost Setup the host interface

The USRP2 communicates at the IP/UDP layer over the gigabit ethernet.
The default IP address of the USRP2 is **192.168.10.2**. You will need
to configure the host's Ethernet interface with a static IP address to
enable communication. An address of **192.168.10.1** and a subnet mask
of **255.255.255.0** is recommended.

On a Linux system, you can set a static IP address very easily by using
the 'ifconfig' command:

    sudo ifconfig <interface> 192.168.10.1

Note that `interface` is usually something like **eth0**. You can
discover the names of the network interfaces in your computer by running **ifconfig**
without any parameters:

    ifconfig -a

<b>Note:</b> When using UHD software, if an IP address for the USRP2 is not
specified, the software will use UDP broadcast packets to locate the
USRP2. On some systems, the firewall will block UDP broadcast packets.
It is recommended that you change or disable your firewall settings.

\subsection usrp2_network_multidev Multiple devices per host

For maximum throughput, one Ethernet interface per USRP2 is recommended,
although multiple devices may be connected via a Gigabit Ethernet
switch. In any case, each Ethernet interface should have its own subnet,
and the corresponding USRP2 device should be assigned an address in that
subnet. Example:

- Configuration for USRP2 device 0:
    -   Ethernet interface IPv4 address: **192.168.10.1**
    -   Ethernet interface subnet mask: **255.255.255.0**
    -   USRP2 device IPv4 address: **192.168.10.2**

- Configuration for USRP2 device 1:
    - Ethernet interface IPv4 address: **192.168.20.1**
    - Ethernet interface subnet mask: **255.255.255.0**
    - USRP2 device IPv4 address: **192.168.20.2**

\subsection usrp2_network_changeip Change the USRP2's IP address

You may need to change the USRP2's IP address for several reasons:
-   to satisfy your particular network configuration
-   to use multiple USRP2s on the same host computer
-   to set a known IP address into USRP2 (in case you forgot)

#### Method 1

To change the USRP2's IP address, you must know the
current address of the USRP2, and the network must be setup properly as
described above. Run the following commands: :

    cd <install-path>/lib/uhd/utils
    ./usrp_burn_mb_eeprom --args=<optional device args> --values="ip-addr=192.168.10.3"

#### Method 2 (Linux Only)

This method assumes that you do not know the
IP address of your USRP2. It uses raw Ethernet packets to bypass the
IP/UDP layer to communicate with the USRP2. Run the following commands:

    cd <install-path>/lib/uhd/utils
    sudo ./usrp2_recovery.py --ifc=eth0 --new-ip=192.168.10.3

\section usrp2_commprob 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 usrp2_commprob_ctrlresponse 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 usrp2_commprob_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 usrp2_commprob_ping Ping the device

The USRP device will reply to ICMP echo requests. 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 usrp2_commprob_uart Monitor the serial output

Read the serial port to get debug verbose output from the embedded
microcontroller. The microcontroller prints useful information about IP
addresses, MAC addresses, control packets, fast-path settings, and
bootloading. Use a standard USB to 3.3v-level serial converter at 230400
baud. Connect **GND** to the converter ground, and connect **TXD** to
the converter receive. The **RXD** pin can be left unconnected as this
is only a one-way communication.

-   **USRP2:** Serial port located on the rear edge
-   **N210:** Serial port located on the left side

\subsection usrp2_commprob_wireshark Monitor the host network traffic

Use Wireshark to monitor packets sent to and received from the device.

\section usrp2_addr Addressing the Device

\subsection usrp2_addr_single 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, resolvable hostname, or by other means. See the
application notes on \ref page_identification.
Please note that this addressing scheme should also be used with the **multi_usrp**
interface.

Example device address string representation for a USRP2 with IPv4
address **192.168.10.2**:

    addr=192.168.10.2

\subsection usrp2_ 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 USRP2s with IPv4
addresses **192.168.10.2** and **192.168.20.2**:

    addr0=192.168.10.2, addr1=192.168.20.2

\section usrp2_mimocable Using the MIMO Cable

The MIMO cable allows two USRP devices to share reference clocks, time
synchronization, and the Ethernet interface. One of the devices will
sync its clock and time references to the MIMO cable. This device will
be referred to as the slave, and the other device, the master.

-   The slave device acquires the clock and time references from the
    master device.
-   The master and slave may be used individually or in a multi-device
    configuration.
-   External clocking is optional and should only be supplied to the
    master device.

\subsection usrp2_mimocable_shared Shared Ethernet mode

In shared Ethernet mode, only one device in the configuration can be
attached to the Ethernet.

-   Clock reference, time reference, and data are communicated over the
    MIMO cable.
-   Master and slave must have different IPv4 addresses in the same
    subnet.

\subsection usrp2_mimocable_dual Dual Ethernet mode

In dual Ethernet mode, both devices in the configuration must be
attached to the Ethernet.

-   Only clock reference and time reference are communicated over the
    MIMO cable.
-   The master and slave must have different IPv4 addresses in different
    subnets.

\subsection usrp2_mimocable_cfgslave Configuring the slave

In order for the slave to synchronize to the master over MIMO cable, the
following clock configuration must be set on the slave device: :

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
    usrp->set_time_source("mimo", slave_index);
    usrp->set_clock_source("mimo", slave_index);
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

\section usrp2_altstream Alternative stream destination

It is possible to program the USRP device to send RX packets to an
alternative IP/UDP destination.

\subsection usrp2_altstream_subnet Set the subnet and gateway

To use an alternative streaming destination, the device needs to be able
to determine if the destination address is within its subnet, and ARP
appropriately. Therefore, the user should ensure that subnet and gateway
addresses have been programmed into the device's EEPROM.

Run the following commands:

    cd <install-path>/lib/uhd/utils
    ./usrp_burn_mb_eeprom --args=<optional device args> --values="subnet=255.255.255.0, gateway=192.168.10.2"

\subsection usrp2_altstream_rxstream Create a receive streamer

Set the stream args "addr" and "port" values to the alternative
destination. Packets will be sent to this destination when the user
issues a stream command.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
    //create a receive streamer, host type does not matter
    uhd::stream_args_t stream_args("fc32");

    //resolvable address and port for a remote udp socket
    stream_args.args["addr"] = "192.168.10.42";
    stream_args.args["port"] = "12345";

    //create the streamer
    uhd::rx_streamer::sptr rx_stream = usrp->get_rx_stream(stream_args);

    //issue stream command
    uhd::stream_cmd_t stream_cmd(uhd::stream_cmd_t::STREAM_MODE_NUM_SAMPS_AND_DONE);
    stream_cmd.num_samps = total_num_samps;
    stream_cmd.stream_now = true;
    usrp->issue_stream_cmd(stream_cmd);
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

<b>Note:</b> Calling `recv()` on this streamer object should yield a timeout.

\section usrp2_hw Hardware Setup Notes

\subsection usrp2_hw_leds Front panel LEDs

The LEDs on the front panel can be useful in debugging hardware and
software issues. The LEDs reveal the following about the state of the
device:

-   **LED A:** transmitting
-   **LED B:** MIMO cable link
-   **LED C:** receiving
-   **LED D:** firmware loaded
-   **LED E:** reference lock
-   **LED F:** CPLD loaded

\subsection usrp2_hw_refclk Ref Clock - 10 MHz

Using an external 10 MHz reference clock, a square wave will offer the
best phase noise performance, but a sinusoid is acceptable. The
reference clock requires the following power level:

-   **USRP2** 5 to 15 dBm
-   **N2XX** 0 to 15 dBm

\subsection usrp2_hw_pps PPS - Pulse Per Second

Using a PPS signal for timestamp synchronization requires a square wave
signal with the following amplitude:

-   **USRP2** 5Vpp
-   **N2XX** 3.3 to 5Vpp

Test the PPS input with the following app:

-   `<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 usrp2_hw_gpsdo Internal GPSDO

Please see \subpage page_gpsdo for information on configuring and using the internal GPSDO.

\section usrp2_misc Miscellaneous

\subsection usrp2_misc_sensors Available Sensors

The following sensors are available for the USRP2/N-Series motherboards;
they can be queried through the API.

-   **mimo_locked** - clock reference locked over the MIMO cable
-   **ref_locked** - clock reference locked (internal/external)
-   other sensors are added when the GPSDO is enabled

\subsection usrp2_misc_multirx Multiple RX channels

There are two complete DDC chains in the FPGA. In the single channel
case, only one chain is ever used. To receive from both channels, the
user must set the **RX** subdevice specification. This hardware has only
one daughterboard slot, which has been aptly named slot **A**.

In the following example, a TVRX2 is installed. Channel 0 is sourced
from subdevice **RX1**, and channel 1 is sourced from subdevice **RX2**
(**RX1** and **RX2** are the antenna ports on the TVRX2 daughterboard):

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~{.cpp}
    usrp->set_rx_subdev_spec("A:RX1 A:RX2");
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

*/
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