Overlay Manager Function Summary; Reducing Overlay Manager Overhead - Analog Devices VisualDSP++ 3.5 Manual

Memory Overlays and Advanced LDF Commands
On completion of the transfer, the overlay manager restores register values
from the run-time stack, flushes the cache, and then jumps the PC to the
run-time location of the referenced function. It is very important to flush
the cache before moving the PC to the referenced function. Otherwise,
when code is replaced or modified, incorrect code execution may occur. If
the program sequencer searches the cache for an instruction and an
instruction from the previous overlay is in the cache, that instruction may
be executed because the expected cache miss is not received.

Overlay Manager Function Summary

In summary, the overlay manager routine does the following.
• Maintains a run-time stack for registers being used by the overlay
manager
• Compares the requested overlay's ID with that of the previously
loaded overlay (stored in the
• Sets up the DMA transfer of the overlay (if it is not already in
internal memory)
• Jumps the PC to the run-time location of the referenced function
These are the basic tasks that are performed by an overlay manager. More
sophisticated overlay managers may be required for individual
applications.

Reducing Overlay Manager Overhead

The example in this section incorporates the ability to transfer one overlay
to internal memory while the core executes a function from another over-
lay. Instead of the core sitting idle while the overlay DMA transfer occurs,
the core enables the DMA, and then begins executing another function.
VisualDSP++ 3.5 Linker and Utilities Manual
for 16-Bit Processors
buffer)
ov_id_loaded
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