User:Callahanp

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What I'm doing:
I am a flight simulation hobbyist currently working on building instruments, gauges, radios and controls for a C172. 

I'll be working on the interface between Flightgear and low level hardware in a panel or cockpit. It is my understanding that others, including core Flightgear developers are also working on this and my efforts will follow, derive from, depend on and I hope contribute in some small way to their work.

Recently I began the effort to fully understand the skills needed to contribute to the Flightgear project's codebase. I know c++ from a course in the early 90's. I'm looking at Kdevelop and QTquick as development tools.

Flightgear Codebase

My area of interest is in Flightgear's code includes:

  • telnet
  • phi
  • reset & re-initialize
  • any method to set or get a property
  • the property tree itself
  • configuration files
  • command line parameters

I'm beginning to look through various parts of the Flightgear code-base to understand how the parts fit together and how supporting libraries are used in the project. I'd like to learn how aircraft data and graphics are integrated into the working program, and how, why and where Nasal scripting is used.

I've installed gdbgui and atom for basic code exploration.

Later I'll try QtQuick and QtCreator

Starting with git clones produced by download_and_compile.sh and the run script it produces, I now have a script which echo's the complete flightgear command line invocation and if desired, starts gdbgui with the generated command.

cmd = "/home/pac1/fg/next/install/flightgear/bin/fgfs \
  --fg-root=/home/pac1/fg/next/install/flightgear/bin/../fgdata/ \
  --log-level=2 \
  --fg-scenery=/home/pac1/fg/next/install/flightgear/bin/../fgdata/Scenery \
  --fg-aircraft=/home/pac1/fg/next/install/flightgear/bin/../fgdata/Aircraft \
  --fg-aircraft=~/.fgfs/Aircraft/org.flightgear.fgaddon/Aircraft \
  --httpd=5401 --telnet=5400 --airport=KSFO"
 gdbgui "$cmd"

I start by stepping through the bootstrap and other initialization routines until flightgear is running.


the gdb run command gets things going in gdbgui. Just type "r"

I'm going to record a list of functions called, in the order they are called in with descriptions where appropriate. to get information about where these functions are located, I'll use the atom's project search or the step into feature of gdbgui. If the call is along the main line of execution, it will be in Bold Face. Paths start with directories under flightgear/src, except for /simgear which is under /simgear. Yes there is a simgear/simgear in the path. There's proably a reason why its not simgear/src

bootstrap.cxx

Full Text of Call Called Function Location or Include File Notes
command line in bootstrap.cxx
main(argc, argv)
bootstrap.cxx contains the main function. main.cxx does not.
detectSIMD() bootstrap.cxx returns true if the cpu supports sse2.
gethostname(_hostname, 256) unistd.h glibc returns the hostname of your computer
signal(SIGPIPE, SIG_IGN) signal.h directs SIGPIPE to the SIG_IGN signal handler - Portability: use sigaction() instead
signal(SIGSEGV, segfault_handler) signal.h Flightgear formats the message with a backtrace and exits with std:abort()
segfault_handler (int signo) bootstrap.cxx
initFPE(flightgear::Options::checkForArg(argc, argv, "enable-fpe")) main/options.cxx
bootstrap.cxx
checks the command line arguments for the enable-fpe option. Calls InitFPE with the result.
see bootstrap.cxx for more details
signal(SIGFPE, handleFPE) signal.h
bootstrap.cxx
We handle Floating Point Exceptions
setlocale(LC_ALL, "")
setlocale(LC_NUMERIC, "C")
setlocale(LC_COLLATE, "C")
return fgUninstall() fg_init.cxx Command line options are checked to determine if uninstall should be called.
sglog() /simgear/debug/logstream.cxx This initializes the log. see logstream.cxx for details
std::set_terminate(fg_terminate); <exception>
bootstrap.cxx
sets the standard template library terminate routine
atexit(fgExitCleanup) stdlib.h
bootstrap.cxx
registers the given function to be called at normal process termination, either via exit(3) or via return from the program's main(). Functions so registered are called in the reverse order of their registration; no arguments are passed
fgviewerMain(argc, argv) flightgear/Viewer/fgviewer.cxx see viewer topics for details. This is called in bootstrap.cxx if the command line arguments include --viewer
fgMainInit(argc, argv) Main/main.cxx Starts to initialize flightgear. This is called in bootstrap.cxx if command line arguments do not contain --viewer
catch block various termination for most or all errors. Read the end of bootstrap.cxx for more information
flightgear::shutdownQtApp() bootstrap
Qt
Done separately from atexit. see bootstrap.cxx for more information
crInstall(&info)
crUninstall()
CrashRpt.h #if defined(HAVE_CRASHRPT). This only happens on windows.

Main/main.cxx

Progress on Cockpit Building

As of Feb 1, 2018:

  • I've done only a few prototype circuits
  • have been working to develop skills I'll need to produce a realistic cockpit.
  • Developing skills in Fusion 360 to support 3d Printing and 3d machine tools.
  • Working on tests for a cluster based on Raspberry Pi Zeros
  • Beginning to use a 3d Router
  • Milling into thin prisms and hand polishing disks of plexiglass for illuminating dials in Sim Instruments

As part of my Cockpit Building efforts, I'm also working on

Contact

Maybe our projects overlap and maybe I can be of help you in some small way. I love bouncing ideas back and forth in personal or public e-mails. Feel free to contact me about your non-commercial simulation projects.
Email Callahanp through the wiki

I show up occasionally on #flightgear on irc.flightgear.org and am a member of several public forums related to cockpit building.

Callahanp (talk) 09:45, 11 November 2017 (EST)

My Skills
  • Programming in whatever language is available
  • Databases
  • Making the following list of chips do what they do:
  • MCP23XXX Multiplexer
  • MAX7219 Serially Interfaced, 8-Digit LED Display Driver
  • Designing a few types of circuits that work on a breadboard (see electronics below)
My Developing Skills -- Beginner
  • Grokking Flightgear's code base.
  • Very basic machining on a lathe or mill - no significant experience
  • Electronics - Basics - DC, High & Low speed digital circuits, motor control, emi suppression and mitigation
  • Soldering - Learn to deal with small components
  • Designing circuits that make it from breadboard to cockpit.
  • Getting a cokpit project off the ground
  • C++ - Updating coding skills from an early version of C++
  • Avoiding Writing Howtos
My Developing Skills -- Making Gppd Progress
  • Fusion 360 3dCad
  • 3d Router
The Howtos -- Oh yeah... those...

I'm working on these along side building my cockpit. Some of the early attempts were not that useful. My current approach is to build and document actual hardware. I hope this will be more helpful.

Current Projects:

See below for the my personal rules about these howtos going forward. I had to write these because it was becoming a morass and time waster.

The following is yet another work in progress

Writing Advice to Callahanp from Callahanp  or How to write a Howto.

Rule 1. Brevity.

Rule 2. Real Hardware. If I haven't done it yet I'll talk about it on my personal wiki page. That's where stuff like that belongs.

Rule 3. Project Planning, Building Teams, and anything else about developing a hobby project belong elsewhere. If you want to write about these things, go ahead, but don't do it in a Howto on building something specific like a cockpit. If you haven't done the project yet you'll get it wrong. Plus, you'll sound like a...

Rule 4. Grand visions, Vaporware, Abstract thinking, Advice and other nonsense don't belong anywhere.

Rule 5. Get rid of your darlings. Those witty turns of phrase, that elegant prose, the puns, jokes and asides. Fun to write maybe but not so fun to read. They're distractions. These are things a skillful writer can weave into an uninterrupted smooth train of thought but you're not that good a writer. Don't even try,

'nuff said.