# Building PX4#

## Source code#

Getting the PX4 source code is easy:

sudo apt-get install git
git clone https://github.com/PX4/PX4-Autopilot.git --recursive
bash ./PX4-Autopilot/Tools/setup/ubuntu.sh --no-sim-tools
cd PX4-Autopilot

Now to build it you will need the right tools.

## PX4 Build tools#

The full instructions are available on the dev.px4.io website, but we've copied the relevant subset of those instructions here for your convenience.

(Note that BashOnWindows) can be used to build the PX4 firmware, just follow the BashOnWindows instructions at the bottom of this page) then proceed with the Ubuntu setup for PX4.

## Build SITL version#

Now you can make the SITL version that runs in posix, from the Firmware folder you created above:

make px4_sitl_default none_iris

Note: this build system is quite special, it knows how to update git submodules (and there's a lot of them), then it runs cmake (if necessary), then it runs the build itself. So in a way the root Makefile is a meta-meta makefile :-) You might see prompts like this:

 *******************************************************************************
*   IF YOU DID NOT CHANGE THIS FILE (OR YOU DON'T KNOW WHAT A SUBMODULE IS):  *
*   Hit 'u' and <ENTER> to update ALL submodules and resolve this.            *
*   (performs git submodule sync --recursive                                  *
*    and git submodule update --init --recursive )                            *
*******************************************************************************
Every time you see this prompt type 'u' on your keyboard.

It shouldn't take long, about 2 minutes. If all succeeds, the last line will link the px4 app, which you can then run using the following:

make px4_sitl_default none_iris

And you should see output that looks like this:

creating new parameters file
creating new dataman file

______  __   __    ___
| ___ \ \ \ / /   /   |
| |_/ /  \ V /   / /| |
|  __/   /   \  / /_| |
| |     / /^\ \ \___  |
\_|     \/   \/     |_/

px4 starting.

18446744073709551615 WARNING: setRealtimeSched failed (not run as root?)
ERROR [param] importing from 'rootfs/eeprom/parameters' failed (-1)
Command 'param' failed, returned 1
SYS_AUTOSTART: curr: 0 -> new: 4010
SYS_MC_EST_GROUP: curr: 2 -> new: 1
INFO  [dataman] Unkown restart, data manager file 'rootfs/fs/microsd/dataman' size is 11797680 bytes
BAT_N_CELLS: curr: 0 -> new: 3
CAL_GYRO0_ID: curr: 0 -> new: 2293768
CAL_ACC0_ID: curr: 0 -> new: 1376264
CAL_ACC1_ID: curr: 0 -> new: 1310728
CAL_MAG0_ID: curr: 0 -> new: 196616


so this is good, first run sets up the px4 parameters for SITL mode. Second run has less output. This app is also an interactive console where you can type commands. Type 'help' to see what they are and just type ctrl-C to kill it. You can do that and restart it any time, that's a great way to reset any wonky state if you need to (it's equivalent to a Pixhawk hardware reboot).

## ARM embedded tools#

If you plan to build the PX4 firmware for real Pixhawk hardware then you will need the gcc cross-compiler for ARM Cortex-M4 chipset. You can get this compiler by PX4 DevGuide, specifically this is in their ubuntu_sim_nuttx.sh setup script.

After following those setup instructions you can verify the install by entering this command arm-none-eabi-gcc --version. You should see the following output:

arm-none-eabi-gcc (GNU Tools for Arm Embedded Processors 7-2017-q4-major) 7.2.1 20170904 (release) [ARM/embedded-7-branch revision 255204]
Copyright (C) 2017 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

## Build PX4 for ARM hardware#

Now you can build the PX4 firmware for running on real pixhawk hardware:

make px4_fmu-v4

This build will take a little longer because it is building a lot more including the NuttX real time OS, all the drivers for the sensors in the Pixhawk flight controller, and more. It is also running the compiler in super size-squeezing mode so it can fit all that in a 1 megabyte ROM !!

One nice tid bit is you can plug in your pixhawk USB, and type make px4fmu-v2_default upload to flash the hardware with these brand new bits, so you don't need to use QGroundControl for that.

## Some Useful Parameters#

PX4 has many customizable parameters (over 700 of them, in fact) and to get best results with AirSim we have found the following parameters are handy:

// be sure to enable the new position estimator module:
param set SYS_MC_EST_GROUP 2

// increase default limits on cruise speed so you can move around a large map more quickly.
param MPC_XY_CRUISE 10
param MPC_XY_VEL_MAX 10
param MPC_Z_VEL_MAX_DN 2

// increase timeout for auto-disarm on landing so that any long running app doesn't have to worry about it
param COM_DISARM_LAND 60

// make it possible to fly without radio control attached (do NOT do this one on a real drone)
param NAV_RCL_ACT 0

param set SYS_LOGGER 1