RealTime Operating Systems

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Lecture 10 Real-Time Operating Systems Example
Windows NT RT Extension Windows CE
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• Real-Time Operating System (RTOS)
• Most moderate and complex RT systems have RTOS.
• Some functions of RTOS are similar to normal OS
• -Managing interfaces to the low-level hardware.
• - Scheduling and preempting tasks.
• -Memory management.
• -Providing common services I/O, standard
  devices(keyboard, printer) .
• Some functions of RTOS differ
• -Scaleability.
• -Scheduling policies and synchronization methods.
• -Support for embedded, diskless target
  environment.
• -RTOS is tailored and optimized for embedded
  systems.
• -RTOS provides the ability to boot from ROM.
• -Many RTOS can operate from ROM.

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• Scaleability
• RTOS is structured so that only the needed
  components are included in the RTOS image
  executing on the target.
• Kernelthe innermost core, provides the most
  essential features of the RTOS.
• Other features are added as necessary.
• Scaleability makes RTOS widely applicable to
  small, single-processor applications and to
  large, distrubuted ones.
• RTOS vendors call this microkernal architecture,
  emphasizing the small size of the minimalist
  kernel.

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• Scheduling
• RTOS most commonly provide priority-based
  preemption for control of scheduling.
• The higher priority task always preempts the
  lower-priority tasks when the former becomes
  ready.
• Average performance is a secondary concern.
• The primary concern is that system meet all
  computational deadlines, even in the absolute
  worst case.

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• Typical RTOS features
• Hardware independence
• Scaleable architecture
• Resource management (Memory Allocation)
• Concurrent management
• Data-access control and protection
• Time management
• Networking
• I/O services and file systems
• High-level language support libraries
• Graphics tools

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Real-Time Operating System (RTOS)
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• RT Kernel
• Provides deterministic scheduling and execution
  of RT threads within RT processes.
• 2. Real-time application, C and C libraries
• Gives direct access to the RT kernel services for
  RT threads
• 3. NTX library
• provides RT extensions for the Win32 API that
  allow Windows NT threads to communicate and
  exchange data with RT threads within the
  application.
• 4. Transport driver
• A driver that converts information to the
  protocol needed by the specified transport
  mechanism

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5. Transport mechanism The communication protocol
or method used by NTX to communicate between
Windows NT and RT threads. Whether the various
portions of your INTime applications reside on a
single PC, or on multiple computers accessed vie
serial or Ethernet cable, NTX provides this
essential communication. 6. Modified Windows NT
hardware abstraction layer(HAL) A special
version of the Windows NT HAL that improves the
overall reliability and robustness of an INTime
node, allowing RT threads to continue executing
properly even if Windows NT crashes.
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