Donald White Arizona State University

Implementation Of A Lower Level Architecture

For TheSombrero Single Address Space

Operating System

Donald White

Arizona State University

08/11/2005 Donald White Thesis Defense Arizona State University

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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


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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


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Development Environment• Boot Loader

– Replace ARC SDK with gcc

• PALCode– Replace EBSDK with gcc

• Tools– Object Strip– ARC– ARCDOS– SOSRMAKE


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Development Environment

• Ethereal– Open Source Protocol Analyzer– Plug-in Dissector for Sombrero Protocols

• Revision Control– Subversion– Apache with WebDAV– TortiseSVN– SSL for Controlled Access


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• 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


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W2K Host

NT Development Alpha

NT and Sombrero

Target Alpha

Linux Development Alpha

Boot Loader and PALCode

Source Upload

Module Compile

Sombrero NIC

Component

W2K Host

Sombrero Target Alpha

Linux Development Alpha

Source Upload

Sombrero

Compile

Sombrero NIC


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Lower Level Architecture

• Design Approach– Exploit Sombrero Object Oriented Nature– Represent Hardware Components as Software

Objects– Implement Abstract Objects using Concrete

Objects


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• Mainboard - DEC164SX

• Processor - DEC21164

• System Core Logic - DEC21174

• ISA Bus Controller - CY82C693


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DEC21164

DRVPCIBUS

DEC164SX

CY82C693

DRVISABUS

DEC21174


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• Mainboard Services– map_irq

• Maps PCI device and function to system IRQ

– map_irq_to_ipl• Maps system IRQ to interrupt priority level


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• Processor Services– read_ICSR– write_ICSR– read_MCSR– write_MCSR– read_amask


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• System Core Logic Services– start_timer– enable_irq– disable_irq– get_isa_interrupt– pci_cfg_io_setup– pci_cfg_io_status


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• ISA Bus Controller Services– init8259as– enable_isa_irq– disable_isa_irq– ack_isa_irq– set_irq_trigger_mode


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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


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• 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


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• Interrupt Thread Models– Active Model

• device driver loops blocking and servicing interrupts

– Passive Model• device driver uses calling thread


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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


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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


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• Device Objects– Network Interface Card - DRV3C905

• Ethernet interface

– Real Time Clock - DRVRTC• provides wall-clock time

– Serial Port - DRVUART• asynchronous character input and output


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DRVUART

DRVRTC

DRVPCIBUS

DEC21174CY82C693

DRVISABUS DRV3C905


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• 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


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• ISA Bus– Passive model driver

• Demultiplexes ISA Interrupts

• Handles ISA bus controller interactions

– Services• register_isa_irq

• unregister_isa_irq

• wait_for_interrupt


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• 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


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• 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


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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


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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


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Protocol Component Architecture

• Ethernet – DRV8023

• Internet Protocol – DRVIP

• Address Resolution Protocol – DRVARP

• User Datagram Protocol – DRVUDP

• Internet Control Message Protocol – DRVICMP

• Sombrero Protocol - DRVSPD


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Protocol Component ArchitectureSPD

UDP

IP

Ethernet(RFC894)

3C905

ICMP

ARP


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• 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


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• 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


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• 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


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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


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• DRVICMP– Active model driver

• daemon thread started during protocol stack initialization

• responds to echo requests (pings)

– Services• none


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• DRVSPD– Passive model driver– Implements Sombrero protocols for

communication with host system


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– 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


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Sombrero Protocol Description

• Protocol stack assembly– Components register with SOSBroker during

system construction– Components resolve dependencies during

system initialization


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• Message protocol– Transparent transfer of messages up to 1024

octets– Stop-and-wait protocol– Acknowledgement timer to trigger

retransmission


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• 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


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• 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


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• 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


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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


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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

Documents

Donald White Arizona State University