VxWorks is a real-time operating system used in devices like automobiles and network switches. VxWorks 5 uses a monolithic kernel with real addressing and no virtual memory, while VxWorks 6 adds an MMU and full virtual memory support. VxWorks 5 uses first-fit memory allocation that can cause fragmentation, while VxWorks 6 uses a best-fit algorithm for less fragmentation. VxWorks 6 also includes enhancements like automatic resource reclamation, user-mode heap support, and tighter integration with error management.

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