Typical Memory Layout
sysPhysMemTop()
sysMemTop()
FREE_RAM_ADRS
RAM_LOW_ADRS
LOCAL_MEM_LOCAL_ADRS
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9-2
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.
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9-3
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.
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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.
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9-5
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
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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
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9-7
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.
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9-8
Fine Tuning

For fast, deterministic allocation of fixed size buffers, use
message queues instead of malloc( ).
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9-9
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.
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Creating a Memory Partition
PART_ID memPartCreate (pPool, size)
pPool
size
Pointer to memory for this partition.
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.
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Managing Memory Partitions

System partition management routines call routines listed
below, specifying the PART_ID as memSysPartId.
Generic
memPartAlloc( )
memPartFree( )
memPartShow( )
memPartAddToPool( )
memPartOptionsSet( )
memPartRealloc( )
memPartFindMax( )
System Memory Pool
malloc( )
free( )
memShow( )
memAddToPool( )
memOptionsSet( )
realloc( )
memFindMax( )
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Example Creating a Memory Partition
->partId =memPartCreate(pMemory,100000)
new symbol “partId” added to symbol table.
partId = 0x23ff318: value = 37745448 = 0x23ff328 = partId
+ 0x10
->ptr=memPartAlloc(partId,200)
new symbol “ptr” added to symbol table.
ptr = 0x23ff2ec: value = 37652632 = 0x23e8898
->show partId
status
bytes
----------current
free
99776
alloc
208
cumulative
alloc
208
blocks
-------
ave block
---------
max block
-----------
1
1
99776
208
99776
-
1
208
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9-13
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.
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9-14