2. Typical Memory Layout sysPhysMemTop() sysMemTop() FREE_RAM_ADRS
RAM_LOW_ADRS
LOCAL_MEM_LOCAL_ADRS
Many of the above macros are parameters for the component /hardware/memory/BSP Memory Configuration.
The macro LOCAL_MEM_LOCAL_ADRS is the address of the start of RAM on your board. It is typically equal to 0.
The macro RAM_LOW_ADRS is the address where VxWorks is loaded.
FREE_RAM_ADRS is the address of the end of the VxWorks system image.
Most BSP’s define sysPhysMemTop( ) as the top of physical RAM; sysMemTop( ) is always the top of the system memory pool. The difference is the configurable constant USER_RESERVED_MEM.
Low memory often contains the interrupt vector table, and space for the boot line and an exception message. More detailed memory maps are available in the Programmer’s Guide appendix for your CPU architecture.

3. 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.
The target server memory pool helps to reduce memory fragmentation on the target.
WDB_POOL_SIZE is not a component parameter, but can be configured .../target/config/comps/src/configAll.h.

4. 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.
USER_RESERVED_MEM, a parameter for the component /hardware/memory/BSP Memory Configuration, specifies how many bytes below the top of physical RAM the system memory pool ends. The default value is 0.
The local address of off-board memory on a VME bus can be computed as follows:
Read hardware doc to find the VMEbus address of the memory.
Use sysBusToLocalAdrs( ) to compute the local address corresponding to the VMEbus address.
Adding off-board memory to the system memory pool is usually a bad idea. A subsequent call to malloc() will give you a block of either on- board or off-board memory, leaving uncertainty about the worst-case access time to this block. Instead, consider creating a separate partition for this off-board memory.

5. 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.
For 68k boards the overhead for malloc( ) is:
8 byte header per malloc( ).
Always rounds up to a 4 byte boundary.
When block is free, 8 bytes within body may be used for free list links.
Minimum block size is 8 bytes (header) + 8 bytes (free list links) = 16 bytes.
See the memPartLib man page for more information about the overhead for your architecture.

6. void memOptionsSet (options)
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
Bitwise OR options together to get more than one.
Setting any MEM_BLOCK_XXX option automatically causes the MEM_BLOCK_CHECK option to be set.

7. Examining Memory Use the Browser.
Enter the memory partition ID in the Show box.
System Memory
Pool Size
Currently
Allocated
Free Blocks
Total
Free List
The VxWorks system memory partition ID is memSysPartId.
Total target memory usage within both the target server pool and the system memory pool is displayed with bar graphs in the browser.

8. 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.
A possible race condition can arise between calls to memFindMax( ) and malloc( ).

9. Fine Tuning
For fast, deterministic allocation of fixed size buffers, use message queues instead of malloc( ).
Create a library “bufferLib” of routines for managing your buffers. For example:
/* pBlock points to memory for array of buffers (NULL => malloc) */
/* Put addresses of buffers in a message queue */
/* Returned BUF_ID contains the newly created msgQId */
BUF_ID bufCreate (pBlock, numBufs, bufSize);
/* Calls msgQReceive() to get next buffer */
void *bufGet (bufId);
/* Calls msgQSend() to return the buffer */
void bufReturn (bufId, ptr);
Alternative: Implement your own fixed-size block allocator, guarding the block free-list with a mutex, taskLock(), or intLock().

10. 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.

11. 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 board’s RAM.
PART_ID, defined in memLib.h, is a handle to the memory partition being created.
Specify nonzero USER_RESERVED_MEM to reserve memory at the top of RAM for your application’s exclusive use.

12. 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( )

13. Example Creating a Memory Partition
->partId =memPartCreate(pMemory,100000)
new symbol “partId” added to symbol table.
partId = 0x23ff318: value = = 0x23ff328 = partId + 0x10
->ptr=memPartAlloc(partId,200)
new symbol “ptr” added to symbol table.
ptr = 0x23ff2ec: value = = 0x23e8898
->show partId
status bytes blocks ave block max block
current
free
alloc
cumulative
alloc
Partition information can also be obtained using the memory-partition browser.

14. 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.