Typical Memory Layout

1
Typical Memory Layout
sysPhysMemTop() sysMemTop() FREE_RAM_ADRS
RAM_LOW_ADRS LOCAL_MEM_LOCAL_ADRS
2
Target Server Memory Pool

• A pool of memory on the target reserved for use
  by the Tornado tools
• Dynamic loading of object modules.
• Passing string arguments to tasks spawned on
  target.
• Creation of variables from WindSh.
• The target server manages the pool, keeping
  overhead such as block lists on the host.
• The initial size of the target server memory pool
  is configured by WDB_POOL_SIZE. The default is
  1/16 of sysMemTop( ) - FREE_RAM_ADRS.
• Additional memory is silently allocated from the
  system memory pool if needed.

3
System Memory Pool

• Used for dynamic memory allocation in programs
• malloc( ).
• Creating tasks (stack and TCB).
• VxWorks memory requests.
• Initialized at system start-up.
• Can modify USER_RESERVED_MEM to reserve memory
  for application-specific use.
• May need to modify sysPhysMemTop( ) (or just
  LOCAL_MEM_SIZE) when adding memory to your board.
  Check your BSP documentation.
• To add off-board memory
• void memAddToPool (pPool, poolSize)
• pPool must be the local address of the memory.

4
Allocating/Releasing Memory

• To dynamically allocate memory
• void malloc (nBytes)
• Returns a pointer to the newly allocated memory
  or NULL on error.
• Uses first-fit algorithm.
• Free memory is stored in a linked list.
• Some (small) overhead for each malloc( ).
• To release allocated memory
• void free (ptr)
• Adjacent blocks are coalesced.

5
Debugging Options

• Default malloc( ) debugging If request too
  large, log an error message.
• Default free( ) debugging
• Check block for consistency.
• If corrupted suspend task, log error message.
• Can change default debugging options with
• void memOptionsSet (options)
• Options can be
• MEM_ALLOC_ERROR_LOG_FLAG
• - MEM_ALLOC_ERROR_SUSPEND_FLAG
• MEM_BLOCK_CHECK
• MEM_BLOCK_ERROR_LOG_FLAG
• MEM_BLOCK_ERROR_SUSPEND_FLAG

6
Examining Memory

• Use the Browser.
• Enter the memory partition ID in the Show box.

System Memory Pool Size Currently Allocated
Free Blocks Total
Allocated Free List
7
Additional System Memory Management Routines

• void calloc (nElems, size) Allocate zeroed
  memory for an array.
• void realloc (ptr, newSize) Resize an allocated
  block. The block may be moved.
• int memFindMax( ) Returns the size of the
  largest free block in system memory.

8
Fine Tuning

• For fast, deterministic allocation of fixed size
  buffers, use message queues instead of malloc( ).

9
Generic Partition Manager

• VxWorks provides low-level routines to create and
  manipulate alternate memory pools.
• High-level routines like malloc( ) and free( )
  call these lower level routines, specifying the
  system memory pool.
• Application may use alternate memory partitions
  to reduce fragmentation.
• Application may use alternate memory partitions
  to manage memory with different properties.

10
Creating a Memory Partition

• PART_ID memPartCreate (pPool, size)
• pPool Pointer to memory for this partition.
• size Size of memory partition in bytes.
• Returns a partition id (PART_ID), or NULL on
  error.
• The memory for this partition (pPool) may be
  taken from
• A separate memory board.
• A block allocated from the system memory
  partition.
• The top of the CPU boards RAM.

11
Managing Memory Partitions

• System partition management routines call
  routines listed below, specifying the PART_ID as
  memSysPartId.
• Generic System Memory Pool
• memPartAlloc( ) malloc( )
• memPartFree( ) free( )
• memPartShow( ) memShow( )
• memPartAddToPool( ) memAddToPool( )
• memPartOptionsSet( ) memOptionsSet( )
• memPartRealloc( ) realloc( )
• memPartFindMax( ) memFindMax( )

12
Example Creating a Memory Partition

• -gtpartId memPartCreate(pMemory,100000)
• new symbol partId added to symbol table.
• partId 0x23ff318 value 37745448 0x23ff328
  partId 0x10
• -gtptrmemPartAlloc(partId,200)
• new symbol ptr added to symbol table.
• ptr 0x23ff2ec value 37652632 0x23e8898
• -gtshow partId
• status bytes blocks ave block max block
• ------ ------ ------- --------- -----------
• current
• free 99776 1 99776 99776
• alloc 208 1 208 -
• cumulative
• alloc 208 1 208 -

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Summary

• Standard C routines are used for dynamic memory
  allocation.
• To configure the system memory pool
• Modify sysPhysMemTop( ).
• Specify USER_RESERVED_MEM.
• Call memAddToPool( ).
• For fast, deterministic allocation of fixed size
  buffers, use message queues instead of malloc( ).
• Create separate memory partition for off-board
  memory, or to help reduce fragmentation.