AN2345 Freescale Semiconductor / Motorola, AN2345 Datasheet - Page 22

• Manufacturer Part Number: AN2345
• Description: Real-Time Memory Manager for StarCore DSPs
• Manufacturer: Freescale Semiconductor / Motorola

VSMM Benchmarking
22
Another important aspect of the VSMM is the overall memory efficiency. For this portion of our
benchmarking, we statically created two heaps of sufficient size to allocate thirty-two 230-byte buffers
and four 16 KB buffers. The number of memory blocks and their associated sizes were chosen because
they represent actual numbers used within the Motorola 3G Symbol Rate Real-Time Demo System.
Table 7 details the VSMM heap requirements to support these buffer allocations.
The overhead associated with the memory sizes noted in Table 7 is listed in Table 8. VSMM adds 8 bytes
to each allocated memory block (buffer), so if you allocate a memory block of 1,024 bytes within the
VSMM, the heap requires a memory block of at least 1,032 bytes.
The VSMM always performs an 8-byte alignment of the memory blocks, so when you create a heap with
block sizes of 230 bytes, the actual block sizes created are 232 bytes. Therefore, if you allocate a buffer of
230 bytes, the VSMM returns a buffer of 240 bytes (including 232 bytes plus the 8-byte overhead).
However, only 232 bytes of this returned buffer are available to your application. The VSMM uses the
remaining 8 bytes to define the memory block heap.
Table 9 presents the total cycles for each VSMM task when critical method 2 is used. As noted earlier,
critical method 2 is the most cycle intensive of the five predefined critical methods. Table 10 presents the
overall statistics for each VSMM module. The C module cycle numbers were collected with argument
verification enabled, critical method 1 defined, and Level 3 optimization applied. The VSMM requires a
minimum of two heaps, and each heap requires a minimum of two memory blocks. Therefore, the
minimum memory overhead is 24 bytes per heap plus 8 bytes per memory block (2
bytes.
Per heap
Per memory block
Memory initialization
Static heap creation
230-byte partitions
16 KB partitions
Total Memory
Manager
OSE-HM
VSMM
Freescale Semiconductor, Inc.
Heap
For More Information On This Product,
Table 9. VSMM Task Cycles With Critical Method 2 Enabled
Type
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Table 6. Code Space Requirements
Table 7. Heap Size Requirements
Task
Table 8. Associated Overhead
Code Space Requirements (Bytes)
VSMM (Bytes)
VSMM Heap Size (Bytes)
24
8
65,592
73,296
1,428
2,352
7,704
VSMM Cycles
OSE-HM (Bytes)
24) + (4
167
30
2,048
16
8) = 80