build.txt

= Building GPSD from source =

This is a guide to building GPSD from a bare source tree.  It includes
guidance on how to cross-build the package.

Some hints for people building binary packages are in packaging/readme.txt.

(This file is marked up in asciidoc.)

== Quick start ==

Under Linux, assuming you have all your build prerequisites in place,
this line will do:

   scons && scons check && sudo scons udev-install

If you get any errors, you need to read the detailed instructions that follow.

If 'scons' fails, it is possible that your target system has moved to
Python 3 as its default 'python' interpreter, but you can work around
it by saying "python2 /usr/bin/scons" or something similar.  GPSD's
own Python scripts assume that "#!/usr/bin/env python2" will invoke a
Python 2 interpreter.

== Supported platforms ==

Native-build success should be expected on the following platforms,
provided you have the prerequisites listed in the next section
installed:

* Any desktop or server Linux distribution.
* OpenWRT and derivatives such as CeroWRT.
* FreeBSD, NetBSD, OpenBSD
* Android, using the official Google toolchain from the NDK

We consider failure to build and function on any of these platforms
a serious bug; if you encounter it, please complain on the
development list.

Port difficulty to any system conforming to POSIX-2001.1 should be minimal.

A Cygwin port is in progress but not complete.

Cross-compilation to embedded Linuxes (in addition to the OpenWRT family)
is usually fairly straightforward. An illustrative build transcript
is included at the end of this file.

== Check your build prerequisites ==

Necessary components for any build:

|============================================================================
|C compiler         | gpsd and client library are written in C
|Python 2.x, x >= 6 | some code is generated from python scripts
|scons              | for executing the build recipe
|============================================================================

Note: There must be a Python 2 interpreter named 'python' in your path,
or the regression tests will fail.  On some systems you might need to
arrange this by putting symlink in a local directory on $PATH.

=== C compiler ===

C99 conformance is required in the compiler. The C code depends on one
C11 feature (supported by GCC, clang, and pretty much any C compiler
that also speaks C++): anonymous unions.  We could eliminate these,
but the cost would be source-level interface breakage if we have to
move structure members in and out of unions.

Some portions of the code using shared-memory segments are improved by
the C11 stdatomic.h features for lockless concurrency.  These are: the
SHM export mode in shmexport.c, the code for writing clock corrections
to NTP in ntpshmwrite.c, and the code for reading NTP corrections in
ntpshmread.c. These features have been supported in GCC since 4.7 and
clang since 3.1.

GPSD is normally built and tested with GCC. Do not compile with a version
older than 4.1.1; there are several known issues with older versions,
including (a) non-standards-conformant floating-point generation that
messes up regression testing, (b) a compiler bug affecting RTCM2 code
generation, (c)  the option -Wno-missing-field-initializers is
unavailable, leading to a flood of warnings (this is due to generated
code and cannot be fixed).

clang produces a gpsd that passes all regression tests.

=== Python ===

You will need Python 2.5 or later for the build.

While Python is required to build GPSD from source (the build uses
some code generators in Python), it is not required to run the service
daemon.  In particular, you can cross-compile onto an embedded system
without having to take Python with you.

You will need both basic Python and (if your package system makes the
distinction) the Python development package used for building C
extensions.  Usually these are called "python" and "python-dev". You
will know you are missing the latter if your compilation fails
because of a missing Python.h.

The xgps test client requires the following Python extensions:

|============================================================================
|gobject            | GNOME object introspection library
|pygtk              | Python bindings for GTK
|===========================================================================

=== Scons ===

You will need scons version 2.3.0 (from 2013-03-02) or later to build the code.

=== Optional build components ===

Having the following optional components on your system will enable
various additional capabilities and extensions:

|============================================================================
|C++ compiler     | allows building libgpsmm C++ wrapper for client library
|Qt 4.53+         | allows building libQgpsmm C++ wrapper for client library
|libcap           | Capabilities library, allows 1PPS support under Linux
|curses           | curses screen-painting library, allows building cgps
|============================================================================

If you have libusb-1.0.0 or later, the GPSD build will autodetect
this and use it to discover Garmin USB GPSes, rather than groveling
through /proc/bus/usb/devices (which has been deprecated by the
Linux kernel team).

You can build libQgpsmm if you have Qt (specifically QtCore and
QtNetwork modules) version 4.5.3 or higher.  You will also need a C++
compiler supported by Qt (tested on GCC 4.4.0/mingw on Windows and GCC
4.1.2 on linux). Please refer to Qt's documentation at
http://qt.nokia.com/doc/4.6/platform-specific.html for platform
specific building documentation

For working with DBUS, you'll need the DBUS development
headers and libraries installed.  Under Debian/Ubuntu these
are the packages libdbus-1-dev and libdbus-glib-1-dev.

Under Ubuntu, the ncurses package you want is libncurses5-dev.  Under
Fedora, it's ncurses-devel.  Depending on how your distribution
packages ncurses you may also require libtinfo5, a separate terminfo
library.

On some older versions of Ubuntu (notably 11.10) there is a packaging
defect that may cause your build to blow up in SCons. It's a missing
package info file for the tinfo library. To fix this, install the file
packaging/tinfo.pc in /usr/lib/pkgconfig/tinfo.pc. 13.10 fixed this.

We've seen a report that compiling on the Raspberry Pi fails with
a complaint about curses.h not being found.  You need to install
Raspbian's curses development library if this happens.

For building from the source tree, or if you change the man page
source, xslt and docbook xsl style files are used to generate nroff
-man source from docbook xml.  The following packages are used in this
process:

|============================================================================
|libxslt            | xsltproc is used to build man pages from xml
|docbook-xsl        | style file for xml to man translation
|xmlto              | DocBook formatter program
|asciidoc           | DocBook front end with lighter markup
|============================================================================

The build degrades gracefully in the absence of any of these. You should
be able to tell from scons messages which extensions you will get.

Under Ubuntu and most other Debian-derived distributions, an easy way
to pick up the prerequisites is: "apt-get build-dep gpsd".  Note
that your sources.list will need "deb-src" lines for this, not
just "deb" lines.

If you are custom-building a Linux kernel for embedded deployment, you
will need some subset of the following modules:

|============================================================================
|pl2303     | Prolific Technology, Inc. PL2303 Serial Port
|ftdi_sio   | FTDI 8U232AM / FT232
|cypress_m8 | M8/CY7C64013
|cp210x     | Cygnal Integrated Products devices
|garmin_gps | Garmin USB mice including GPS-18
|cdc_am     | USB Communication Device Class Abstract Control Model interface
|============================================================================

These are listed in rough order of devices covered as of 2013; the
PL23203 by itself accounts for over 70% of deployed USB mice.  We
recommend building with pl2303, ftdi_sio, cypress_m8, and cp210x.

We've receive a bug report that suggests the Python test framework
requires legacy PTY support (CONFIG_LEGACY_PTYS) from the Linux
kernel.  You should make sure you're in the 'dialout' group in order
to have permission to use these devices.

== How to build the software from source ==

To build gpsd for your host platform from source, simply call 'scons'
in a working-directory copy. (Cross-build is described in a later
section.)

To clean the built files, call 'scons -c' .  To clean scons' cache,
call 'scons sconsclean'.  Doing both should return your working directory
to a near pristine state as far as building is concerned.  Some user
created files may remain, and source code changes will not have been
reverted..

You can specify the installation prefix, as for an autotools build, by
running "scons prefix=<installation_root>". The default value is
"/usr/local".  The environment variable DESTDIR also works in the
usual way.

If your linker run fails with missing math symbols, see the FIXME
comment relating to implicit_links in the scons recipe; you probably
need to build with implicit_link=no.  If this happens, please report
your platform, ideally along with a way of identifying it from Python,
to the GPSD maintainers.

If, while building, you see a complaint that looks like this:

--------------------------------------------------------------------
I/O error : Attempt to load network entity http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd
--------------------------------------------------------------------

it means the xmlto document formatter is failing to fetch a stylesheet it
needs over the network. Probably this means you are doing a source
build on a machine without live Internet access.  The workaround
for this is to temporarily remove xmlto from your command path so GPSD
won't try building the documentation.  The actual fix is to install
DocBook on your machine so there will be a local copy of the
stylesheet where xmlto can find it.

After building, please run 'scons check' to test the correctness
of the build.  It is not necessary to install first.  Python is
required for regression tests. If any of the tests fail, you probably
have a toolchain issue.  The most common such problem is failures of
strict C99 conformance in floating-point libraries.

Once you have verified that the code is working, "scons install"
will install it it in the system directories. "scons uninstall" will
undo this. Note: because scons is a single-phase build system, this
may recompile everything. If you want feature-configuration options,
you need to specify them here.

To enable hotplugging of USB GPSes under Linux, you may do 'scons
udev-install' to put the appropriate udev rules and wrapper files in
place.

You will need php and php-gd installed to support the PHP web page.
included with the distribution. To install it, copy the file
'gpsd.php' to your HTML document directory. Then see the
post-installation instructions in INSTALL for how to configure it.

== The leapseconds cache ==

Early in your build, the recipe will try to go over the Internet to
one of several sources of current data on the leap-second offset in
order to ensure that the file leapseconds.cache is up to date.  This,
in turn, is used to build a timebase.h include file.

This procedure may fail if you are building in a network that
requires an authenticating web proxy.  If that occurs, the build will
time out with a warning and a suggestion to use the leapfetch=no build
option.

Building with leapfetch=no may, in unusual circumstances, result in
reported GPS time being off by a second or more.  The circumstances
are:

1. It has been less than 20 minutes since power-up; the GPS has
   not yet received the current leapsecond offset as part of the
   periodic ephemeris download.

2. One or more leap-second offset increments have been issued between
   when your GPSD source tree was cloned from the repository (or
   leapsecond.cache was later updated) and now.  Leap-second
   increments, compensating for minute and unpredictable changes in
   the Earth's rotation, are occasionally issued by international time
   authorities.

Note that the same failure can occur with any GPSD installation.  But
by refreshing leapseconds.cache you reduce the error window for
leap-second offset bumps to affect your installation so that it begins
as late as possible, at your build time rather than from when the
source tree was copied.

If you have had a leap-second transition, the following regression tests
will break:

	  bu303-climbing.log
	  bu303-moving.log
	  bu303-nofix.log
	  bu303-stillfix.log
	  bu303b-nofix.log
	  italk-binary.log
	  navcom.log
	  ublox-aek-4t.log
	  ublox-lea-4t.log
	  ublox-sirf1.log

There is no help for this other than a test rebuild.  The problem is
that these devices rely on the build-time leap-second offset; you'll
see times one second off.  Other GPSes either return
leap-second-corrected time or the test loads include a
leapsecond-offset report before any time is reported.

== Optional features ==

By giving command-line options to scons you can configure certain rarely-used
optional features in, or compile standard features out to reduce gpsd's
footprint. "scons --help" will tell the story; look under "Local Options"
and consult the source code if in doubt.

Here are a few of the more important feature switches.  Each description
begins with the default for the switch.

pps=yes: for small embedded systems and those without threading,
it is possible to build gpsd without thread support if you build
with pps=no.  You'll lose support for updating the clock from PPS
pulses.

dbus_export=no: for systems using DBUS: gpsd includes support for
shipping fixes as DBUS notifications, compiled in by default.  This
may lead to complaint messages during testing  on systems that don't
support DBUS. Build with the option "dbus_export=no" to disable it

qt=yes: libQgpsmm is a Qt version of the libgps/libgpsmm
pair. Thanks to the multi-platform approach of Qt, it allows the gpsd
client library to be available on all the Qt supported platforms.
Please see http://qt.nokia.com/doc/4.6/supported-platforms.html for a
status of Qt supported platforms as of version 4.6.

minimal=yes: people building for extremely constrained environments
may want to set this.  It changes the default for all boolean (feature)
options to false; thus, you get *only* the options you specify on the
command line.  Thus, for example, if you want to turn off all features
except socket export and nmea0183,

------------------------------------------------
scons minimal=yes socket_export=yes nmea0183=yes
------------------------------------------------

will do that.

== Port and toolchain testing ==

'scons check' will run a comprehensive regression-test suite.  You
should do this, at minimum, every time you build from source on a new
machine type.  GPSD does enough bit-twiddling and floating point that
it is very sensitive to toolchain problems; you'll want to be sure
those aren't going to bite you in production.

So the tests will run fast and be easy to do often, we make the test
framework shove data through the pty and socket layers *way* faster
than would ever occur in production.  If you get regression-test
failures that aren't repeatable and look like the test framework is
sporadically failing to feed the last line or two of test loads, try
using the slow=yes option with scons check.  If that fails, try
increasing the delay constants in gps/fake.py.  If you have to do this,
please report your experience to the GPSD maintainers.

For instructions on how to live-test the software, see the file INSTALL.

== Reverting to a clean state ==

The scons equivalent of 'make clean' is 'scons -c' or 'scons
--clean'. This will revert your source tree to a clean state nearly as
though you had just cloned or downloaded it; some scons housekeeping
stuff is left in place.

If you interrupted a regression test, 'scons testclean' will remove
generated test programs.

You can run 'scons sconsclean' to temove most of the configuration
state that scons keeps.  Be aware, however, thatr doing this can
confuse scons; you may need to run 'scons --config=force' afterwards
to make your build succeed.

== Notes on Android:

Samuel Cuella reports:

I use the official google toolchain from the Android NDK (Native
Development Kit). You can also use the toolchain from code sourcery I
guess. I cross-compile from a "regular" (with GNU userland) linux box.

People who port software from linux to android tend to use either the
NDK or code sourcery's.

If you are going to include "official" guidelines, I would go for
recommending the official toolchain from the NDK.

Here are the scons switches I use:

scons wordsize=32 snapshot=off arch=arm sample=shell

scons -j3 prefix=/usr libdir=$prefix/lib udevdir=/lib/udev
gpsd_user=gpsd gpsd_group=uucp socket_export=1
nmea0183=1 sirf=1

With the following environment variables:

TOOL_HOME=/home/samuel/android-official-last/
export TOOL_PREFIX=${TOOL_HOME}/bin/arm-linux-androideabi
export CXX=$TOOL_PREFIX-g++
export AR=$TOOL_PREFIX-ar
export RANLIB=$TOOL_PREFIX-ranlib
export CC=$TOOL_PREFIX-gcc
export LD=$TOOL_PREFIX-ld

export CCFLAGS="-march=armv7-a -mtune=cortex-a8 -mfpu=vfp"
export ARM_TARGET_LIB=${TOOL_HOME}/sysroot

scons wordsize=32 snapshot=off arch=arm sample=shell

== Cross-building ==

The scons recipe is intended to support cross-building, in particular
for embedded deployment of the software.  A session transcript
illustrating how to do that, with some routine messages suppressed and
replaced with [...], follows.  The script assumes you're cloning from the
GPSD project site or a mirror. Notes and explanation follow the transcript.

----
$ git clone [...]
Cloning into gpsd...
[...]
$ cd gpsd
$ cp ../.scons-option-cache .
$ cat .scons-option-cache
libgpsmm = False
libQgpsmm = False
python = False
prefix = '/work/buildroot/output/staging/usr/'
sysroot = '/work/buildroot/output/staging/'
target = 'arm-indigo-linux-gnueabi'
$ scons
scons: Reading SConscript files ...
[...]
Altered configuration variables:
libgpsmm = False (default True): build C++ bindings
libQgpsmm = False (default True): build QT bindings
python = False (default True): build Python support and modules.
prefix = /work/buildroot/output/staging/usr/ (default /usr/local): installation directory prefix
sysroot = /work/buildroot/output/staging (default ): cross-development system root
target = arm-indigo-linux-gnueabi (default ): cross-development target
scons: done reading SConscript files.
scons: Building targets ...
substituter(["jsongen.py"], ["jsongen.py.in"])
chmod -w jsongen.py
chmod +x jsongen.py
rm -f ais_json.i && /usr/bin/python jsongen.py --ais --target=parser > ais_json.i && chmod a-w ais_json.i
Creating 'gpsd_config.h'
arm-indigo-linux-gnueabi-gcc -o ais_json.os -c --sysroot=/work/buildroot/output/staging/ -Wextra -Wall -Wno-uninitialized -Wno-missing-field-initializers -Wcast-align -Wmissing-declarations -Wmissing-prototypes -Wstrict-prototypes -Wpointer-arith -Wreturn-type -D_GNU_SOURCE -O2 -fPIC ais_json.c
arm-indigo-linux-gnueabi-gcc -o daemon.os -c --sysroot=/work/buildroot/output/staging/ -Wextra -Wall -Wno-uninitialized -Wno-missing-field-initializers -Wcast-align -Wmissing-declarations -Wmissing-prototypes -Wstrict-prototypes -Wpointer-arith -Wreturn-type -D_GNU_SOURCE -O2 -fPIC daemon.c
Creating 'gpsd.h'
[...]
chmod -w maskaudit.py
chmod +x maskaudit.py
rm -f gps_maskdump.c && /usr/bin/python maskaudit.py -c . > gps_maskdump.c && chmod a-w gps_maskdump.c
arm-indigo-linux-gnueabi-gcc -o gps_maskdump.os -c --sysroot=/work/buildroot/output/staging/ -Wextra -Wall -Wno-uninitialized -Wno-missing-field-initializers -Wcast-align -Wmissing-declarations -Wmissing-prototypes -Wstrict-prototypes -Wpointer-arith -Wreturn-type -D_GNU_SOURCE -O2 -fPIC gps_maskdump.c
[..]
scons: done building targets.
$ file gpsd
gpsd: ELF 32-bit LSB executable, ARM, version 1 (SYSV), dynamically linked (uses shared libs), for GNU/Linux 2.6.36, not stripped
----

The author of this transcript notes:

The sysroot option tells the compiler and linker to use libraries and
headers from the given path as if they were placed at / prefix. During
this build the option allows linking with target ncurses (with the option
of having more packages at the --sysroot path) and including correct
headers without specifying -I and -L options.

In the options cache file gpsd is configured to install to
/work/buildroot/output/staging/usr path, so gpsd clients could be
compiled against libgps.so using /work/buildroot/output/staging as
sysroot option.

"arm-indigo-linux-gnueabi" as target means that
arm-indigo-linux-gnueabi-gcc and related tools are available in PATH;
your cross-compiler is likely to have a different target prefix.

You may also find it useful to set manbuild=no.

== Autostarting the daemon ==

The preferred way to start gpsd is on-demand by a hotplug script
detecting USB device activations.  Look at the gpsd.rules and
gpsd.hotplug files to see how this is accomplished.  Relevant
productions in the build recipe are "udev-install" and
"udev-uninstall"; relevant build options include "udevdir".

If you for some reason need to start gpsd unconditionally at
boot time (in particular, if you need to support RS232 devices)
there's a model init.d script under packaging/deb and a systemd
setup under systemd/.

// end