How to Perform Real-Time Processing on the Raspberry Pi. Steven Doran SCALE 13X

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1 How to Perform Real-Time Processing on the Raspberry Pi Steven Doran SCALE 13X

2 Outline What is Real-Time? What is the Raspberry Pi? Can the Raspberry Pi handle Real-Time (And why would you want to? Why would you want to use the Raspberry Pi for Real-Time? Example Project Questions 2

3 What is Real-Time? An application that requires a guaranteed response within a strict timing constraints 3

4 Some Examples of Real-Time 4

5 Soft Real Time vs. Hard Real-Time Hard Real-Time If the event is not processed in a strict timing window then bad things will happen Soft Real-Time If the event is not processed in a not as strict timing window then the system may degrade but its not as bad 5

6 Hard Real-Time Example 6

7 Hard Real-Time Example (Gone Wrong) 7

8 Soft Real-Time Example 8

9 What is Real-Time is NOT! #1 Software that runs fast 9

10 What is Real-Time is NOT! Software that runs fast Example: A processing Thread w/ a execution requirement of 2.5ms, but the system can only supports 5.0 ms 10

11 What is Real-Time is NOT! #1 Software that runs fast Example: A processing Thread w/ a execution requirement of 2.5ms, but the system can only supports 5.0 ms #2 Just because it is embedded 11

12 Real-Time Metrics Interrupt Latency Time to process an interrupt Scheduling Latency Time for the OS Scheduler to start a processing task (Nominal and Worst-case) 12

13 What is a Raspberry Pi? The Raspberry Pi is a small computer w/ 700 Mhz Single Core Atom and up to 512 Mb memory all for $25 13

14 Raspberry Pi (The Good) It's cheap It is easy hacked (Easily Configurable) It comes with GPIO connectors for device input / output It supports 1080p video 14

15 Raspberry Pi Projects 15

16 Raspberry Pi (The Bad) No Real-Time Clock Expects device to be always connected to the internet Cannot generate deterministic timing pulses to control things like DC motors RAM cannot be expanded The built-in Network Interface is really a USB device and shares the same bus on any USB device connected to it Power issues especially with the first hardware version 16

cannot be expanded The built-in Network Interface is really a USB device and shares the

17 Can the Raspberry Pi handle Real-Time (And why would you want to?) Kinda with allot of tweaking Current Linux / BSD kernels for the Raspberry Pi do not support real-time Standard Linux or BSD install includes services that generate lots of overhead No real-time clock Because it is cheap and flexible 17

Raspberry Pi do not support real-time Standard Linux or BSD install

18 A Sample Raspberry Pi Project that benefits from Real-Time Nerf Tank Let's say we want to have a Raspberry Pi control a deadly Nerf Tank Pi needs to detect the baddy Pi needs to move the turret to aim the Nerf gun at the baddy Pi needs to fire the deadly Nerf projectile at the baddy (if in range) Pi needs to make sure the tank does not collide with anything while it is doing the above steps Pi needs to do all of the above at the same time (Multi18 threaded)

baddy Pi needs to fire the deadly Nerf projectile at the baddy (if in range) Pi needs to make sure the tank does

19 Nerf Tank Real-Time Problem #1 No Real-Time Clock Problem Statement Nerf Tank will have timing requirements and will not be always (if ever) connected to the Internet Solution Add a Real-Time clock 19

20 Nerf Tank Real-Time Problem #2 Pulse Generation Problem Statement Even with a Real-time clock the Raspberry Pi will not generate the deterministic timing pulses we need to move the drive motors and turret with accuracy Solutions Connect a AD9850 Pulse generator to the Raspberry Pi Connect a AdaFruit Servo HAT to the Raspberry Pi 20

we need to move the drive motors and turret with accuracy Solutions Connect a

21 Nerf Tank Real-Time Problem #2 Pulse Generation 21

22 AD9850 Pulse Generator connected to the Raspberry Pi GPIO GPIO AD9850 ISR Raspberry Pi 22

23 Nerf Tank Real-Time Problem #3 MultiThreaded Applications Problem Statement The software that will control the Nerf Tank will require multiple processing threads with unique timing and priorities that the stock Raspberry Pi distribution kernels cannot guarantee Processing tasks share resources Solutions Use RTEMS Build your own real-time Linux kernel from source Who uses make menuconfig anymore? Remove all unused services 23

24 Fun Example of Priority Inversion 24

25 Real Time Executive for Multiprocessor Systems (RTEMS) for Raspberry Pi Open Source Real Time Operating System (RTOS) Used in Spaceflight, medical, and other real-time embedded applications Ported to the Raspberry Pi (w/ some limitations) 25

26 Nerf Tank Real-Time Problem #4 Maximum CPU Performance Problem Statement The Raspberry Pi's CPU is not set at its maximum performance using default kernels Solutions Overclock the CPU Using RaspBian Raspi-config Remove all unneeded services 26

27 Summary We discussed what Real-Time means We described the Raspberry Pi w/ its Pro's and Con's We used a Nerf Tank example on how to tweak the Raspberry Pi to perform real-time processing 27

28 Questions 28

Deeply Embedded Real-Time Hypervisors for the Automotive Domain Dr. Gary Morgan, ETAS/ESC

Deeply Embedded Real-Time Hypervisors for the Automotive Domain Dr. Gary Morgan, ETAS/ESC 1 Public ETAS/ESC 2014-02-20 ETAS GmbH 2014. All rights reserved, also regarding any disposal, exploitation, reproduction,