Memory management in vx works

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  • that are protected from manipulation or that can3.easily be shared among kernel and process tasks.


  • 1. Dhan V Sagar CB.EN.P2CSE13007
  • 2. Overview   Hard Real Time System from Wind River Systems  Used in automobiles, consumer devices, network switches  Based on a monolithic kernel  VxWorks5 Vs VxWorks6
  • 3. Address Translation  Real Addressing Mode Using a Relocation Register Full Virtual Memory Functionality
  • 4. Memory Management (VxW 5)  • No Swapping or Paging • Assumes that there is enough physical memory available • Does not have a directly supported virtual memory system • Virtual memory support separately as add-on • Kernel is loaded into the bottom part of the memory • System Memory Pool • Dynamic memory routines for manipulating the heap • malloc(), free() are used
  • 5. MMU 
  • 6. MMU page table designs 
  • 7.
  • 8. Memory Allocation  First Fit Allocation (VxWorks 5) • Allocates the first available space • Free blocks can be stored in a simple linked list • Leads to fragmentation • Dynamic partition sizes are allocated on system initialisation • Partition the memory into two or more sections
  • 9. Memory Allocation  Best Fit Allocation (VxWorks 6) Smallest-sized block that is big enough to satisfy the request More complex data structure to store the free blocks Whenever a new size is created, a new node is inserted in the tree Probability of a larger block having to be split is smaller Free blocks of the same size can be grouped together
  • 10. Memory Allocation  Best Fit Allocation (VxWorks 6)
  • 11. Memory Allocation Performance Comparison 
  • 12. Memory Management Enhancements (VxWorks 6)  Automatic resource reclamation   Improved memory allocation using a “best-fit” algorithm  User-mode heap and memory partition support  Developer-replaceable user-mode heap allocator  Heap instrumentation for heaps and memory partitions in both the kernel  and RTPs  Tight integration with error management
  • 13. Memory Protection  o MMU-based memory protection provides isolation of the kernel from user-mode applications and of applications from each other, increasing device reliability. o VxWorks’ preemptive, priority-based global task scheduler ensures real-time deterministic behavior. o The ability to create private or public objects in the kernel and in RTPs offers flexibility to use objects o The extensible system call interface enables application developers to employ custom-developed kernel services from user-mode execution. o Support for shared libraries among RTPs improves code efficiency and reusability