Implementation Of A Lower Level Architecture For The Sombrero Single Address Space Operating System

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

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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

4
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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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

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Development Environment
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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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Lower Level Architecture

• Mainboard - DEC164SX
• Processor - DEC21164
• System Core Logic - DEC21174
• ISA Bus Controller - CY82C693

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Lower Level Architecture
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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

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Lower Level Architecture

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

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Lower Level Architecture

• 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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Lower Level Architecture

• 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 ltIPL, IRQ, GPDgt
• SOSInterrupt provides thread registration and
  deregistration services
• PALCode provides thread blocking and unblocking

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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

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Interrupt Processing Architecture

• 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 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

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Device Driver Architecture
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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

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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

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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

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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

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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 Architecture
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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

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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

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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

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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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Protocol Component Architecture

• DRVICMP
• Active model driver
• daemon thread started during protocol stack
  initialization
• responds to echo requests (pings)
• Services
• none

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Protocol Component Architecture

• DRVSPD
• Passive model driver
• Implements Sombrero protocols for communication
  with host system

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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

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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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Sombrero Protocol Description

• Message protocol
• Transparent transfer of messages up to 1024
  octets
• Stop-and-wait protocol
• Acknowledgement timer to trigger retransmission

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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

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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

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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

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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