Agnostic Device Drivers
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The document discusses Agnostic Device Drivers (ADD), a concept for a slimline boot firmware for Linux on Power Architecture systems. ADD uses a small virtual machine to execute bytecode programs that control low-bandwidth devices like I2C and GPIO in a platform-agnostic way. ADD programs can be packaged in the device tree or inserted at runtime, and the virtual machine can run in hosted mode or as a kernel thread. ADD aims to provide high-level programming capabilities while maintaining flexibility, performance and a small footprint. The document also discusses further opportunities for ADD like real-time support, scheduling, multi-OS compatibility and extended debugging facilities.
Agnostic Device Drivers
- 1. Agnostic Device Drivers ( ADD ) Concept, Design, and Implementation of a Slimline Boot Firmware for Linux on Power Architecture IBM Deutschland Entwicklung GmbH Schoenaicherstr. 220 71032 Boeblingen
- 2. Contents Open Firmware Standard Existing Hardware Abstraction Concepts Agnostic Device Drivers (ADD) Further Opportunities
- 3. Is Hardware Abstraction necessary?
- 4. Open Firmware Standard IEEE Standard IEEE Std. 1275-1994 Standard for Boot (Initialization Configuration) Firmware Device Interface User Interface Client Interface Device-Tree
- 5. Existing Hardware Abstraction Concepts (based on Open Firmware) Common Hardware Reference Platform: Apple:
- 6. Comparison - - High-Level Language Facilities: -- - Packaging: +/- - Flexibility: ++ - Performance: Platform Expert RTAS
- 7. Agnostic Device Drivers (ADD) – Concept and Basics
- 8. Agnostic Device Drivers (ADD) – Packaging Options 1: ADD byte-code program taken from Device-Tree Packaged with the Firmware Code. Additional Device-Tree properties can include control or execution information. 2: ADD byte-code program inserted during run-time (via user transaction) Fast development of ADD byte-code programs. Flexible packaging.
- 9. Agnostic Device Drivers (ADD) – Virtual Machine Front-End: Loads Byte-Code (from different sources) Virtual Machine: Executes ADD Byte-Code Back-End: Implements I2C and GPIO Binding to the Operating System
- 10. Agnostic Device Drivers (ADD) – Functionality Small footprint virtual machine Controlling of low-bandwidth devices (e.g. I2C or GPIO) is possible Controlling of the policy and the logic of a device is possible Control Structures Defining Words Extended Debug Facilities Virtual Machine runs in hosted mode Virtual Machine runs as kernel thread (root user can interrupt it) I2C Drivers can debugged via I2C Emulation Host Adapter Rebooting during development is not necessary Single execution is not difficult to implement
- 11. Agnostic Device Drivers (ADD) – Summary ++ ++ ++ ++ Agnostic Device Drivers - - High-Level Language Facilities: -- - Packaging: - - Flexibility: ++ - Performance: Platform Expert RTAS
- 12. Questions ???
- 13. Further Opportunities Real-Time / Performance ADD is an asynchronous interface / hardware abstraction. Functionality can implemented as primitive (for real-time applications). Scheduling Scheduling (once, every 5 sec., etc.) can controlled via a Device-Tree property. Thread Support is not difficult to implement (instruction pointer and token-table pointer must saved). Multi-OS Only vendor token-table entries changed. ADD Virtual Machine can integrated into the firmware ADD driver could then used in the firmware and the operating system. Extended Debug Facilities Realizes fast program development and debugging.
- 14. Agnostic Device Drivers (ADD) – Example: Byte Code
- 15. Agnostic Device Drivers (ADD) – Example: Linux Kernel I2C Interface I2C algorithm driver used by the I2C bus driver to talk to the I2C bus. I2C chip driver controls the process of talking to an individual I2C device that lives on an I2C bus.
- 16. Overview of available Options – CHRP (Common Hardware Reference Platform) Based on Open Firmware RTAS (Run-Time Abstraction Service) Hides machine dependent operations behind a machine independent interface, which the operating system can call synchronous. System Firmware = LLFW + Open Firmware + RTAS
- 17. Overview of available Options – RPA (RISC Platform Architecture) Based on CHRP Hypervisor partitions machine resources enables multiple operating systems space for hardware dependent patches only one Hypervisor instance exits for all operating systems Partition Firmware = Open Firmware + RTAS
- 18. LinuxBIOS
- 19. OpenBIOS Maintainer Stefan Reinauer and Patrick Mauritz Main Goal To get a 100% compliant Open Firmware boot firmware. Current Function OpenBIOS could be executed under a boot manager or LinuxBIOS. File System Support Support adopted from Grub and libhfs. PPC Support Rudimentary available from the Mac-On-Linux project.
- 20. Complete Boot Process - Phase 1
- 21. Complete Boot Process - Phase 2
- 22. Complete Boot Process - Phase 3
Editor's Notes
- #2: To replace the title / subtitle with your own: Click on the title block -> select all the text by pressing Ctrl+A -> press Delete key -> type your own text
- #5: Device-Tree: The set of devices attached to the system, including permanently installed devices and plug-in devices, is described by an Open Firmware data structure known as device tree.
- #6: RPA: - implements a Hypervisor - can run several Operating Systems - implements RTAS Apple: - doesn’t implement RTAS and a Hypervisor - has Platform Expert (Hardware and Operating System “Platform Expert” Code, which is copied from the firmware to the kernel of the Operating System, where it is executed)
- #8: Agnostic Device Drivers (ADD) Concept and Basics (1): During the boot phases of the operating system, the Device-Tree (including ADD Byte-Code) is fetched over the client interface of Open Firmware. Device-Tree, with the Byte-Code included, is stored by the operating system and is available after lifetime of Open Firmware. (2): ADD Interpreter loads Byte-Code from the stored Device-Tree. (3): ADD Interpreter executes Byte-Code asynchronous.
- #11: Control Structures: - Finite loop incrementing by 1 - Finite loop incrementing by <n> - Indefinite loop terminating when <f> is 'true‘ - Indefinite loop terminating when <f> is 'false‘ - Infinite loop - Two-branch conditional Defining Words: - Variables - Constants - Colon Definitions (Sub-Routines)