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Realtime doc
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Felix Mauch
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Tristan Schnell
Tristan Schnell
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ur_rtde_driver/doc/real_time.md
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ur_rtde_driver/doc/real_time.md
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# Setting up Ubuntu with a PREEMPT_RT kernel
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In order to run the `universal_robot_driver`, we highly recommend to setup a ubuntu system with
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real-time capabilities. Especially with a robot from the e-Series the higher control frequency
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might lead to non-smooth trajectory execution if not run using a real-time-enabled system.
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You might still be able to control the robot using a non-real-time system. This is, however, not recommended.
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To get real-time support into a ubuntu system, the following steps have to be performed:
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1. Get the sources of a real-time kernel
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2. Compile the real-time kernel
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3. Setup user privileges to execute real-time tasks
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This guide will help you setup your system with a real-time kernel.
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## Preparing
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To build the kernel, you will need a couple of tools available on your system. You can install them
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using
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``` bash
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sudo apt-get install build-essential bc ca-certificates gnupg2 libssl-dev wget
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```
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Before you download the sources of a real-time-enabled kernel, check the kernel version that is currently installed:
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```bash
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$ uname -r
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4.15.0-62-generic
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```
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## Getting the sources for a real-time kernel
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To build a real-time kernel, we first need to get the kernel sources and the real-time patch.
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First, we must decide on the kernel version that we want to use. Above, we
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determined that our system has a 4.15 kernel installed. However, real-time
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patches exist only for selected kernel versions. Those can be found on the
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[linuxfoundation wiki](https://wiki.linuxfoundation.org/realtime/preempt_rt_versions).
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In this example, we will select a 4.14 kernel. Select a kernel version close to the
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one installed on your system.
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Go ahead and download the kernel sources, patch sources and their signature files:
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```bash
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$ wget https://cdn.kernel.org/pub/linux/kernel/projects/rt/4.14/patch-4.14.139-rt66.patch.xz
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$ wget https://cdn.kernel.org/pub/linux/kernel/projects/rt/4.14/patch-4.14.139-rt66.patch.sign
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$ wget https://www.kernel.org/pub/linux/kernel/v4.x/linux-4.14.139.tar.xz
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$ wget https://www.kernel.org/pub/linux/kernel/v4.x/linux-4.14.139.tar.sign
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```
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To unzip the downloaded files do
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```bash
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$ xz -d patch-4.14.139-rt66.patch.xz
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$ xz -d linux-4.14.139.tar.xz
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```
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### Verification
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Technically, you can skip this section, it is however highly recommended to verify the file
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integrity of such a core component of your system!
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To verify file integrity, you must first import public keys by the kernel developers and the patch
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author. For the kernel sources use (as suggested on
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[kernel.org](https://www.kernel.org/signature.html))
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```bash
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gpg2 --locate-keys torvalds@kernel.org gregkh@kernel.org
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```
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and for the patch search for a key of the author listed on
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[linuxfoundation wiki](https://wiki.linuxfoundation.org/realtime/preempt_rt_versions).
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```bash
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$ gpg2 --keyserver hkp://keys.gnupg.net --search-keys zanussi
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gpg: data source: http://51.38.91.189:11371
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(1) German Daniel Zanussi <german.zanussi@globant.com>
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4096 bit RSA key 0x537F98A9D92CEAC8, created: 2019-07-24, expires: 2023-07-24
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(2) Michael Zanussi <mzanussi@gmail.com>
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4096 bit RSA key 0x7C7F76A2C1E3D9EB, created: 2019-05-08
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(3) Tom Zanussi <tzanussi@gmail.com>
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Tom Zanussi <zanussi@kernel.org>
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Tom Zanussi <tom.zanussi@linux.intel.com>
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4096 bit RSA key 0xDE09826778A38521, created: 2017-12-15
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(4) Riccardo Zanussi <riccardo.zanussi@gmail.com>
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2048 bit RSA key 0xD299A06261D919C3, created: 2014-08-27, expires: 2018-08-27 (expired)
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(5) Zanussi Gianni <g.zanussi@virgilio.it>
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1024 bit DSA key 0x78B89CB020D1836C, created: 2004-04-06
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(6) Michael Zanussi <zanussi@unm.edu>
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Michael Zanussi <mzanussi@gmail.com>
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Michael Zanussi <michael_zanussi@yahoo.com>
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Michael Zanussi <michael@michaelzanussi.com>
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1024 bit DSA key 0xB3E952DCAC653064, created: 2000-09-05
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(7) Michael Zanussi <surfpnk@yahoo.com>
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1024 bit DSA key 0xEB10BBD9BA749318, created: 1999-05-31
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(8) Michael B. Zanussi <surfpnk@yahoo.com>
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1024 bit DSA key 0x39EE4EAD7BBB1E43, created: 1998-07-16
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Keys 1-8 of 8 for "zanussi". Enter number(s), N)ext, or Q)uit > 3
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```
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Now we can verify the downloaded sources:
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```bash
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$ gpg2 --verify linux-4.14.139.tar.sign
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gpg: assuming signed data in 'linux-4.14.139.tar'
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gpg: Signature made Fr 16 Aug 2019 10:15:17 CEST
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gpg: using RSA key 647F28654894E3BD457199BE38DBBDC86092693E
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gpg: Good signature from "Greg Kroah-Hartman <gregkh@kernel.org>" [unknown]
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gpg: WARNING: This key is not certified with a trusted signature!
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gpg: There is no indication that the signature belongs to the owner.
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Primary key fingerprint: 647F 2865 4894 E3BD 4571 99BE 38DB BDC8 6092 693E
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$ gpg2 --verify patch-4.14.139-rt66.patch.sign
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gpg: assuming signed data in 'patch-4.14.139-rt66.patch'
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gpg: Signature made Fr 23 Aug 2019 21:09:20 CEST
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gpg: using RSA key 0x0129F38552C38DF1
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gpg: Good signature from "Tom Zanussi <tom.zanussi@linux.intel.com>" [unknown]
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gpg: aka "Tom Zanussi <zanussi@kernel.org>" [unknown]
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gpg: aka "Tom Zanussi <tzanussi@gmail.com>" [unknown]
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gpg: WARNING: This key is not certified with a trusted signature!
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gpg: There is no indication that the signature belongs to the owner.
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Primary key fingerprint: 5BDF C45C 2ECC 5387 D50C E5EF DE09 8267 78A3 8521
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Subkey fingerprint: ACF8 5F98 16A8 D5F0 96AE 1FD2 0129 F385 52C3 8DF1
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```
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## Compilation
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Before we can compile the sources, we have to extract the tar archive and apply the patch
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```bash
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$ tar xf linux-4.14.139.tar
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$ cd linux-4.14.139
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$ xzcat ../patch-4.14.139-rt66.patch.xz | patch -p1
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```
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Now to configure your kernel, just type
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```bash
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$ make oldconfig
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```
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This will ask for kernel options. For everyting else then the `Pereemption Model` use the default
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value (just press Enter) or adapt to your preferences. For the preemption model select `Fully Preemptible Kernel`:
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```bash
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Preemption Model
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1. No Forced Preemption (Server) (PREEMPT_NONE)
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> 2. Voluntary Kernel Preemption (Desktop) (PREEMPT_VOLUNTARY)
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3. Preemptible Kernel (Low-Latency Desktop) (PREEMPT__LL) (NEW)
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4. Preemptible Kernel (Basic RT) (PREEMPT_RTB) (NEW)
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5. Fully Preemptible Kernel (RT) (PREEMPT_RT_FULL) (NEW)
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choice[1-5]: 5
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```
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Now you can build the kernel. This will take some time...
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```bash
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$ make -j `getconf _NPROCESSORS_ONLN` deb-pkg
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```
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After building, install the `linux-headers` and `linux-image` packages in the parent folder (only
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the ones without the `-dbg` in the name)
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```bash
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$ sudo apt install ../linux-headers-4.14.139-rt66_*.deb ../linux-image-4.14.139-rt66_*.deb
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```
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## Check for preemption capabilities
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After you have built your custom kernel, boot into it and make sure that the kernel has indeed
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```bash
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$ uname -v | cut -d" " -f1-4
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#1 SMP PREEMPT RT
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```
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## Setup user priviliges to use real-time scheduling
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To be able to schedule threads with user privileges (what the driver will do) you'll have to change
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the user's limits by changing `/etc/security/limits.conf` (See [the manpage](https://manpages.ubuntu.com/manpages/bionic/man5/limits.conf.5.html) for details)
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We recommend to setup a group for realtime users instead of writing a fixed username into the config
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file:
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```bash
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$ sudo groupadd realtime
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$ sudo usermod -aG realtime $(whoami)
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```
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Then, make sure `/etc/security/limits.conf` contains
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```
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@realtime soft rtprio 99
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@realtime soft priority 99
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@realtime soft memlock 102400
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@realtime hard rtprio 99
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@realtime hard priority 99
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@realtime hard memlock 102400
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```
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Note: You will have to log out and log back in (Not only close your terminal window) so these
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changes will take effect.
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## Setup GRUB to always boot the realtime kernel
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To make the new kernel the default kernel that the system will boot into every time, you'll have to
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change the grub config file inside `/etc/default/grub`.
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But first, let's find out the name of the entry that we will want to make the default. You can list
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all available kernels using
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```bash
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$ awk -F\' '/menuentry |submenu / {print $1 $2}' /boot/grub/grub.cfg
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menuentry Ubuntu
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submenu Advanced options for Ubuntu
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menuentry Ubuntu, with Linux 4.15.0-62-generic
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menuentry Ubuntu, with Linux 4.15.0-62-generic (recovery mode)
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menuentry Ubuntu, with Linux 4.15.0-60-generic
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menuentry Ubuntu, with Linux 4.15.0-60-generic (recovery mode)
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menuentry Ubuntu, with Linux 4.15.0-58-generic
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menuentry Ubuntu, with Linux 4.15.0-58-generic (recovery mode)
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menuentry Ubuntu, with Linux 4.14.139-rt66
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menuentry Ubuntu, with Linux 4.14.139-rt66 (recovery mode)
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menuentry Memory test (memtest86+)
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menuentry Memory test (memtest86+, serial console 115200)
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menuentry Windows 7 (on /dev/sdc2)
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menuentry Windows 7 (on /dev/sdc3)
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```
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From the output above, we'll need to generate a string with the pattern `"submenu_name>entry_name"`. In our case this would be
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```
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"Advanced options for Ubuntu>Ubuntu, with Linux 4.14.139-rt66"
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```
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**The double quotes and no spaces around the `>` are important!**
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With this, we can setup the default grub entry and then update the grub menu entries. Don't forget this last step!
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```bash
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$ sudo sed -i 's/^GRUB_DEFAULT=.*/GRUB_DEFAULT="Advanced options for Ubuntu>Ubuntu, with Linux 4.14.139-rt66"/' /etc/default/grub
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$ sudo update-grub
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```
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