uhd

    general.rst

========================================================================

UHD - General Application Notes

========================================================================

.. contents:: Table of Contents

------------------------------------------------------------------------

Finding devices

------------------------------------------------------------------------

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Device addressing

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Deviced are addressed through key/value string pairs.

These string pairs can be used to narrow down the search for a specific device or group of devices.

Most UHD utility applications and examples have a --args parameter that takes a device address;

where the device address is expressed as a delimited string.

* See the documentation in types/device_addr.hpp for reference.

* See device-specific application notes for usage.

**Example:**

::

    serial=0x1234, type=usrpx

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Device discovery

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Devices attached to your system can be discovered using the "uhd_find_devices" program.

The find devices program scans your system for supported devices and prints

out an enumerated list of discovered devices and their addresses.

The list of discovered devices can be narrowed down by specifying device address args.

**Usage:**

::

    uhd_find_devices

    -- OR --

    uhd_find_devices --args <device-specific-address-args>

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Device properties

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Properties of devices attached to your system can be probed with the "uhd_usrp_probe" program.

The usrp probe program contructs an instance of the device and prints out its properties;

properties such as detected daughter-boards, frequency range, gain ranges, etc...

**Usage:**

::

    uhd_usrp_probe --args <device-specific-address-args>

------------------------------------------------------------------------

Misc notes

------------------------------------------------------------------------

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Process scheduling

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

The UHD will try to automatically boost the process's scheduling priority.

Currently, this is only supported on platforms with *sched.h*.

When setting the priority fails, the UHD prints out an error.

This error is harmless, it simply means that your process will have a normal scheduling priority.

**Linux Notes:**

Non-privileged users need special permission to change the scheduling priority.

Add the following line to */etc/security/limits.conf*:

::

    @<my_group>    -    rtprio    99

Replace <my_group> with a group to which your user belongs.

Settings will not take effect until the user has logged in and out.

Application Notes

* `General App Notes <./general.html>`_

# Setup defines for process scheduling

########################################################################

MESSAGE(STATUS "Configuring process scheduling...")

INCLUDE(CheckIncludeFileCXX)

CHECK_INCLUDE_FILE_CXX(sched.h HAVE_SCHED_H)

IF(HAVE_SCHED_H)

    MESSAGE(STATUS "  Process scheduling supported through sched_setscheduler.")

    ADD_DEFINITIONS(-DHAVE_SCHED_H)

ELSE(HAVE_SCHED_H)

    MESSAGE(STATUS "  Process scheduling not supported.")

ENDIF(HAVE_SCHED_H)

########################################################################

    ${CMAKE_CURRENT_SOURCE_DIR}/sched.cpp

//

// Copyright 2010 Ettus Research LLC

//

// This program is free software: you can redistribute it and/or modify

// it under the terms of the GNU General Public License as published by

// the Free Software Foundation, either version 3 of the License, or

// (at your option) any later version.

//

// This program is distributed in the hope that it will be useful,

// but WITHOUT ANY WARRANTY; without even the implied warranty of

// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

// GNU General Public License for more details.

//

// You should have received a copy of the GNU General Public License

// along with this program.  If not, see <http://www.gnu.org/licenses/>.

//

#include <uhd/utils/static.hpp>

#include <stdexcept>

#include <iostream>

#ifdef HAVE_SCHED_H

#include <sched.h>

/*

 * # /etc/security/limits.conf

#

@usrp   -       rtprio  99

*/

UHD_STATIC_BLOCK(setup_process_sched){

    try{

        int policy = SCHED_RR;

        int max_pri = sched_get_priority_max(policy);

        if (max_pri == -1) throw std::runtime_error("sched_get_priority_max with SCHED_RR failed");

        sched_param sp; sp.sched_priority = max_pri;

        int ss_ret = sched_setscheduler(0, policy, &sp);

        if (ss_ret == -1) throw std::runtime_error("sched_setscheduler with SCHED_RR failed");

    }

    catch(const std::exception &e){

        std::cerr << "Process scheduling error: " << e.what() << std::endl;

    }

}

#endif /* HAVE_SCHED_H */