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Chapter 4 - SOFTWARE PROJECT MANAGEMENT
P default counter is set to hex 200 and mapped to internal memory. Base addresses can
also be established with the linker memory control file.
The linker reads each input object file, placing the header file in internal P memory and
combining the overlay modules into a contiguous block loaded into external X memory at
location 100 hexadecimal. Any labels or jumps within the overlay blocks are resolved to
addresses relative to the relocatable symbol OVLBASE. Since OVLBASE is the first load
P memory address it is assigned the value 200 hexadecimal. The linker does not guarantee that a given symbol or section will begin at a particular location unless that information
is explicitly specified in the linker memory control file. For more information on specific
linker operations see the Motorola DSP Linker/Librarian Reference Manual.
4.8
EXAMPLE 3: BOOTSTRAP OVERLAY
Many Motorola DSP processors, specifically those with RAM-based program memory,
support a bootstrap mode of operation. This involves mapping a built-in ROM-based bootstrap program into P memory, executing the program to move user-supplied code from
another location (usually EPROM) into program RAM, then transferring control to the user
program. Because the user program is loaded in one location (e.g. EPROM) but moved
to another for execution, it is a natural application for assembly language overlay semantics. Another wrinkle in bootstrap mode is that user instruction words are loaded in bytewise fashion, such that the load location counter must be incremented by bytes rather
MOTOROLA
DSP ASSEMBLER REFERENCE MANUAL
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