Analog Devices VisualDSP++ 3.5 Manual page 209

Memory Overlays and Advanced LDF Commands
processors do not have a separate built-in overlay manager, the DMA con-
troller must be used to move code in and out of internal L1 memory. For
this reason, it is almost always better to use the instruction cache.
ADSP-219x DSPs support an external memory interface that allows rather
large amounts of memory, but at a penalty in speed. Internal memory is
ten times faster than external memory, so it may be desirable to keep large
amounts of program code in external memory and to swap parts of it to
internal memory for speed in execution. Such a program is said to run in
" overlays ."
For code reuse and portability, a program should not require modification
to run in different machines or in different locations in memory. There-
fore, the C or assembler source code does not specify the addresses of
either code or data. Instead, the source code assigns names to sections of
code, data, or both at compile or assembly time to allow the linker to
assign physical memory addresses to each section of code or data. The goal
is to make the source program's position independent and to let the linker
assign all the addresses.
The linker uses Linker Description Files to control "what goes where." At
link time, the linker follows directions in the .
data at the proper addresses.
VisualDSP++ 3.5 Linker and Utilities Manual
for 16-Bit Processors
file to place code and
LDF
5-3