Infrastructure Middleware (Part 1): Hardware Abstraction Layer (HAL)

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1 Infrastructure Middleware (Part 1): Douglas C. Schmidt Institute for Software Integrated Systems Vanderbilt University Nashville, Tennessee, USA

2 Learning Objectives in this Part of the Lesson Understand the role the HAL plays in Android s system architecture System Libraries VM & Runtime The HAL mediates interactions between 2 the OS kernel layer & higher layers

economic factors that motivated Google & its original equipment

3 Learning Objectives in this Part of the Lesson Understand the role the HAL plays in Android s system architecture Know the technical & economic factors that motivated Google & its original equipment manufacturer (OEM) partners to add a HAL to the Android software stack 3

Learning Objectives in this Part of the Lesson Understand the role the HAL plays in Android s system architecture Know the technical & economic factors that motivated Google &

4 Learning Objectives in this Part of the Lesson Understand the role the HAL plays in Android s system architecture Know the technical & economic factors that motivated Google & its original equipment manufacturer (OEM) partners to add a HAL to the Android software stack Android apps rarely access the HAL directly, 4 so you needn t know all the details

5 Overview of Android Hardware Abstraction Layer 5

6 The HAL helps to separate concerns in the Android system architecture System Libraries VM Runtime See source.android.com/devices/#hardware 6 Abstraction Layer

7 The HAL helps to separate concerns in the Android system architecture, e.g. Decouples Android platform software from hardware System Libraries VM Runtime 7

8 The HAL helps to separate concerns in the Android system architecture, e.g. Decouples Android platform software from hardware i.e., apps don t break when hardware changes System Libraries VM Runtime 8

9 The HAL helps to separate concerns in the Android system architecture, e.g. Decouples Android platform software from hardware Decouples Android framework layer from the operating system layer System Libraries VM Runtime 9

10 The HAL helps to separate concerns in the Android system architecture, e.g. Decouples Android platform software from hardware Decouples Android framework layer from the operating system layer e.g., this layer can be programmed via method calls on Java objects, rather than C system function calls System Libraries VM Runtime 10

11 The HAL helps to separate concerns in the Android system architecture, e.g. Decouples Android platform software from hardware Decouples Android framework layer from the operating system layer e.g., this layer can be programmed via method calls on Java objects, rather than C system function calls System Libraries VM Runtime App developers can thus focus on business 11 logic, rather than low-level details

12 Android s HAL defines interfaces that driver modules must implement System Libraries VM Runtime See source.android.com/devices/#structure 12

13 Android s HAL defines interfaces that driver modules must implement System Libraries VM Runtime These driver modules do not run 13 in the Android Linux kernel!

14 The Android HAL is a user space library layer, unlike device drivers residing in the Android Linux kernel System Libraries VM Runtime See earlier lesson on the 14 Android Linux Kernel

15 The Android HAL is a user space library layer, unlike device drivers residing in the Android Linux kernel User space code can t directly access Android Linux kernel device drivers System Libraries VM Runtime See earlier lesson on the 15 Android Linux Kernel

16 The Android HAL is a user space library layer, unlike device drivers residing in the Android Linux kernel User space code can t directly access Android Linux kernel device drivers Therefore apps & system services use the HAL to interact w/kernel drivers System Libraries VM Runtime See 16

17 OEMs implement HAL driver modules for their proprietary hardware See source.android.com/devices/#hardware 17 Abstraction Layer

18 OEMs implement HAL driver modules for their proprietary hardware e.g., camera hardware from an OEM has a camera system service & a camera HAL API See source.android.com/devices/camera 18

19 Driver modules that implement HAL APIs are linked dynamically by Android See source.android.com/devices/#modules 19

20 Driver modules that implement HAL APIs are linked dynamically by Android e.g., when an app first accesses the camera hardware encapsulated by the camera HAL API See source.android.com/devices/#modules 20

21 Motivations for Android s Hardware Abstraction Layer 21

22 There are two types of motivations for Android s user space HAL design 22

23 One motivation is technical 23

24 One motivation is technical Shielding higher layers of Android s software stack from Linux kernel idiosyncrasies System Libraries VM & Runtime 24

25 One motivation is technical Shielding higher layers of Android s software stack from Linux kernel idiosyncrasies GNU Linux device drivers don t provide consistent support for certain types of devices It s historical focus is on laptops/desktops/servers System Libraries VM & Runtime 25

26 One motivation is technical Shielding higher layers of Android s software stack from Linux kernel idiosyncrasies GNU Linux device drivers don t provide consistent support for certain types of devices The HAL therefore defines a consistent object-oriented API for these hardware elements System Libraries VM & Runtime 26

27 Another motivation is economic 27

28 Another motivation is economic Kernel device drivers are GPL d See en.wikipedia.org/wiki/gnu_general_public_license 28

29 Another motivation is economic Kernel device drivers are GPL d The GPL requires OEMs give out source code for their drivers See en.wikipedia.org/wiki/gnu_general_public_license 29

use proprietary drivers i.e., they don t want

30 Another motivation is economic Kernel device drivers are GPL d The GPL requires OEMs give out source code for their drivers However, Android OEMs often use proprietary drivers i.e., they don t want to give out the source code for them See hiqes.com/android-linux-kernel-drivers 30

31 Another motivation is economic Kernel device drivers are GPL d The GPL requires OEMs give out source code for their drivers However, Android OEMs often use proprietary drivers Putting driver implementations in user-space HAL enables them no to release the source code System Libraries VM & Runtime See 31

32 Another motivation is economic Kernel device drivers are GPL d The GPL requires OEMs give out source code for their drivers However, Android OEMs often use proprietary drivers Putting driver implementations in user-space HAL enables them no to release the source code See Android licenses for details System Libraries See source.android.com/source/licenses.html 32 VM & Runtime

33 End of Infrastructure Middleware (Part 1): Hardware Abstraction Layer 33

Overview of Layered Architectures

Overview of Layered Architectures Overview of ed Architectures Douglas C. Schmidt d.schmidt@vanderbilt.edu www.dre.vanderbilt.edu/~schmidt Professor of Computer Science Institute for Software Integrated Systems Vanderbilt University Nashville,