Donald White Arizona State University

1. Implementation Of A Lower Level Architecture For TheSombrero Single Address Space Operating System Donald White Arizona State University

2. Outline • Introduction • Development Environment • Lower Level Sombrero Architecture • Interrupt Processing Architecture • Device Driver Architecture • Protocol Component Architecture • Sombrero Protocol Description • Standard Library • Contributions and Conclusions • Future Work Donald White Thesis Defense Arizona State University

3. Introduction • Sombrero is an unconventional OS • Single Address Space • Object Orientation • Current implementation does not always exploit the Sombrero paradigm shift • Design choices based on intuition rather than measurement • Implementation sometimes reflects expediency Donald White Thesis Defense Arizona State University

4. Development Environment • Boot Loader • Replace ARC SDK with gcc • PALCode • Replace EBSDK with gcc • Tools • Object Strip • ARC • ARCDOS • SOSRMAKE Donald White Thesis Defense Arizona State University

5. Development Environment • Ethereal • Open Source Protocol Analyzer • Plug-in Dissector for Sombrero Protocols • Revision Control • Subversion • Apache with WebDAV • TortiseSVN • SSL for Controlled Access Donald White Thesis Defense Arizona State University

6. Development Environment • Simplified Configuration with Enhanced Boot Loader • PCI Bus Scan to find Network Card • UART Driver and Input-Output Library • Real Time Clock • Address Resolution Protocol Support Donald White Thesis Defense Arizona State University

7. Development Environment Donald White Thesis Defense Arizona State University

8. Lower Level Architecture • Design Approach • Exploit Sombrero Object Oriented Nature • Represent Hardware Components as Software Objects • Implement Abstract Objects using Concrete Objects Donald White Thesis Defense Arizona State University

9. Lower Level Architecture • Mainboard - DEC164SX • Processor - DEC21164 • System Core Logic - DEC21174 • ISA Bus Controller - CY82C693 Donald White Thesis Defense Arizona State University

10. DRVISABUS CY82C693 DRVPCIBUS DEC21164 DEC21174 DEC164SX Lower Level Architecture Donald White Thesis Defense Arizona State University

11. Lower Level Architecture • Mainboard Services • map_irq • Maps PCI device and function to system IRQ • map_irq_to_ipl • Maps system IRQ to interrupt priority level Donald White Thesis Defense Arizona State University

12. Lower Level Architecture • Processor Services • read_ICSR • write_ICSR • read_MCSR • write_MCSR • read_amask Donald White Thesis Defense Arizona State University

13. Lower Level Architecture • System Core Logic Services • start_timer • enable_irq • disable_irq • get_isa_interrupt • pci_cfg_io_setup • pci_cfg_io_status Donald White Thesis Defense Arizona State University

14. Lower Level Architecture • ISA Bus Controller Services • init8259as • enable_isa_irq • disable_isa_irq • ack_isa_irq • set_irq_trigger_mode Donald White Thesis Defense Arizona State University

15. Interrupt Processing Architecture • Interrupt as Synchronization Object • sparse three dimensional matrix <IPL, IRQ, GPD> • SOSInterrupt provides thread registration and deregistration services • PALCode provides thread blocking and unblocking Donald White Thesis Defense Arizona State University

16. Interrupt Processing Architecture • PALCode Services • block interrupt thread • promotion • block and demote • block and switch • demotion • schedule interrupt thread • dispatch of interrupt to appropriate thread • unblock interrupt thread • supports wakeup on time expiration Donald White Thesis Defense Arizona State University

17. Interrupt Processing Architecture • Interrupt Thread Models • Active Model • device driver loops blocking and servicing interrupts • Passive Model • device driver uses calling thread Donald White Thesis Defense Arizona State University

18. Interrupt Thread Architecture • Observations • May increase latency when interrupt thread also performs “bottom half” processing • Active model requires one thread per device • Passive model may have different threads for transmit and receive sides of a device • Multiplexed interrupts may require a demultiplexing software layer Donald White Thesis Defense Arizona State University

19. Device Driver Architecture • Infrastructure Objects • PCI Bus - DRVPCIBUS • support for drivers for PCI bus attached devices • uses system core logic services • performs PCI enumeration • validates device resource assignments • ISA Bus - DRVISABUS • support for drivers for ISA bus attached devices • uses PCI bus and ISA bus controller services Donald White Thesis Defense Arizona State University

20. Device Driver Architecture • Device Objects • Network Interface Card - DRV3C905 • Ethernet interface • Real Time Clock - DRVRTC • provides wall-clock time • Serial Port - DRVUART • asynchronous character input and output Donald White Thesis Defense Arizona State University

21. DRVUART DRVISABUS DRVRTC DRV3C905 DRVPCIBUS CY82C693 DEC21174 Device Driver Architecture Donald White Thesis Defense Arizona State University

22. Device Driver Architecture • PCI Bus • Passive model driver • Services • reserve_device • transfers control of device to driver • PCI configuration address space access • PCI input-output address space access Donald White Thesis Defense Arizona State University

23. Device Driver Architecture • ISA Bus • Passive model driver • Demultiplexes ISA Interrupts • Handles ISA bus controller interactions • Services • register_isa_irq • unregister_isa_irq • wait_for_interrupt Donald White Thesis Defense Arizona State University

24. Device Driver Architecture • Network Interface Card • Passive model driver • Services • DRV3C905Send • waits for a free ring buffer if necessary • copies the contents of a buffer chain into a ring buffer • DRV3C905Receive • waits for a full ring buffer if necessary • copies the contents of a ring buffer into a buffer chain • GetMACAddress • returns Ethernet address Donald White Thesis Defense Arizona State University

25. Device Driver Architecture • Real Time Clock • Active model driver • driver thread loops blocking on RTC interrupt and copying current time to local storage • Services • get_time • returns current time of day Donald White Thesis Defense Arizona State University

26. Device Driver Architecture • Serial Port • Active model driver • Driver thread loops servicing UART interrupts • Circular transmit and receive buffers • Calling threads may be blocked on semaphores • Provided “raw” and “cooked” modes of operation • Services • ioctl – configures driver and serial port • read – transfers characters from UART • write – transfers characters to UART Donald White Thesis Defense Arizona State University

27. Standard Input-Output Library • Provided user for serial port driver • Modeled after C runtime library • Services • Low level • gets – read string • puts – write string • High level • printf and variations • scanf and variations Donald White Thesis Defense Arizona State University

28. Protocol Component Architecture • Ethernet – DRV8023 • Internet Protocol – DRVIP • Address Resolution Protocol – DRVARP • User Datagram Protocol – DRVUDP • Internet Control Message Protocol – DRVICMP • Sombrero Protocol - DRVSPD Donald White Thesis Defense Arizona State University

29. SPD ICMP UDP IP ARP Ethernet (RFC894) 3C905 Protocol Component Architecture Donald White Thesis Defense Arizona State University

30. Protocol Component Architecture • DRV8023 • Passive Model Driver • Provides RFC 894 Ethernet framing • Services • EtherSend • adds framing and calls lower layer • EtherRecv • removes framing and based on frame type switches to correct thread and returns to appropriate higher layer • GetMacAddress • returns local Ethernet address Donald White Thesis Defense Arizona State University

31. Protocol Component Architecture • DRVIP • Passive model driver • Minimal Internet Protocol Implementation • Services • IPIn • adds packet header and calls lower layer • IPOut • removes header and based on protocol switches to correct thread and returns to appropriate higher layer Donald White Thesis Defense Arizona State University

32. Protocol Component Architecture • DRVARP • Active model driver • daemon thread started during protocol stack initialization • responds to ARP requests • Services • NetMACLookup • returns Ethernet address corresponding to an IP address • generates ARP request if necessary Donald White Thesis Defense Arizona State University

33. Protocol Component Architecture • DRVUDP • Passive model driver • Minimal User Datagram Protocol implementation • Services • UDPIn • adds datagram header and calls lower layer • UDPOut • removes datagram header and based on destination port switches to correct thread and returns to appropriate higher layer Donald White Thesis Defense Arizona State University

34. Protocol Component Architecture • DRVICMP • Active model driver • daemon thread started during protocol stack initialization • responds to echo requests (pings) • Services • none Donald White Thesis Defense Arizona State University

35. Protocol Component Architecture • DRVSPD • Passive model driver • Implements Sombrero protocols for communication with host system Donald White Thesis Defense Arizona State University

36. Protocol Component Architecture • Services • MsgToHost • adds message header and calls lower layer output service • calls lower layer input service to receive acknowledgement • WaitForMsgFromHost • allocates message header buffer and calls lower layer input service • sends acknowledgement • MsgFromHostTimer • DataToHost • DataFromHost Donald White Thesis Defense Arizona State University

37. Sombrero Protocol Description • Protocol stack assembly • Components register with SOSBroker during system construction • Components resolve dependencies during system initialization Donald White Thesis Defense Arizona State University

38. Sombrero Protocol Description • Message protocol • Transparent transfer of messages up to 1024 octets • Stop-and-wait protocol • Acknowledgement timer to trigger retransmission Donald White Thesis Defense Arizona State University

39. Sombrero Protocol Description • Burst protocol • Transparent transfer of large virtual address regions • Retransmit-N protocol • 8 megabyte bursts of up to 8192 fragments containing up to 1024 octets • Acknowledgement bitmap following burst Donald White Thesis Defense Arizona State University

40. Sombrero Protocol Description • Evaluation • Send side of protocol stack realized Sombrero potential for reduced context switching through use of passive service model • Receive side of protocol stack showed degraded performance after addition of ARP and ICMP components due to increased thread switching and data movement Donald White Thesis Defense Arizona State University

41. Sombrero Protocol Description • Evaluation continued • Observations of equilibrium condition during which message transfers fail to progress • Receiving thread cannot get control at appropriate layer before desired message is discarded • Implementation weaknesses • potential buffer overflow in burst protocol • data leakage between threads • unnecessary data movement Donald White Thesis Defense Arizona State University

42. Contributions and Conclusions • Provided future researchers with an improved development environment • Documented previously undocumented features of Sombrero design and implementation • Provided a lower-level architecture implementation for Sombrero • Demonstrated successful application of Sombrero interrupt processing architecture • Identified architectural weaknesses in Sombrero protocol stack Donald White Thesis Defense Arizona State University

43. Future Work • Preliminary loader using DHCP and TFTP • Minimally intrusive trace facility • Cross platform development tools • Add PALCode Validity Checker to toolkit • Object representation of physical memory • ATA over Ethernet client driver to support persistent storage Donald White Thesis Defense Arizona State University