1. Real Time Android
Akshar
24/8/11

2. Objective
• Having an Android based device capable of
running hard real time tasks

3. Why?
• Robust embedded linux kernel
• Community supported open souce native
libraries
• Well thought partitioning between managed
and unmanaged code
• Well developed/documented APIs for HMI.

4. What Android lacks
• Safety Critical features
• Real-Time kernel
• Not much support of digital analog I/O. wired
interfaces etc. [typically required in SCRT
scenarios]

5. Android Kernel

6. Android Kernel
• 2.6.25 kernel modified specifically for low
power, low CPU, portable devices.
• Translates to 75 edits and 88 new file
additions
• 5 changes to scheduler mostly to the run-
queue locking
• IPC Binder is new feature by Google.

7. Android Applications
• Each Android app is a process
• Scheduled by the underlying Linux scheduler
(SCHED_OTHER)
• Memory management however is done by
Dalvik VM

8. Applications in android

9. RT Suitability
• Android Kernel uses the same Completely Fair
Scheduler of Linux 2.6
• The libc implementation for Android is called
bionic and it does not support process level
mutexes but supports thread level mutexes
and conditions.
• No implementation of priority inheritance/
ceiling is present

10. Possible Approache

11. Available hypervisors
• RTAI
• RT-Linux
• RT patch set for linux
• Our own SParK

12. RTAI
• RTAI patch is not compatible with android
kernel out of the box. [Already tried that]

13. RT patch set (PREEMPT_RT)
• Uses 2.6’s new features such as
CONFIG_PREEMPT
• Well documented
• Seems doable at the moment

14. SPaRK
• Can it run a rich non RT OS like android on top
of it ?
• Documentation?
• Community Support?

15. To Summarize
• Can we build a system with one periodic HARD
REAL TIME task along with Android?
– For simplicity we will assume that this task will not
share any resources with other Android Processes.

16. References
• http://www.linuxjournal.com/magazine/real-time-linux-kernel-
scheduler
• Evaluating Android for Real Time Applications (OSPERT -2010)
• http://embedded-computing.com/android-rtos-duo-todays-
medical-devices
• Reliable Real-Time Applications on Android OS
• An In-Vehicle Infotainment Software Architecture Based on Google
Android
• http://www.ibm.com/developerworks/linux/library/l-completely-
fair-scheduler/
• http://www.ibm.com/developerworks/linux/library/l-cfs/index.html
• http://www.scandevconf.se/db/Marakana-Android-Internals.pdf