RTEMS CPU Architecture Supplement
The small memory model is the simplest and most
efficient. However, it includes a limitation that
make it inappropriate for numerous applications. The
small memory model assumes that the application needs
to access no more than 64K words. Thus the dp
register can be loaded at application start time
and never reloaded. Thus the compiler will not
even generate instructions to load the dp.
This can significantly reduce the code space required by an application but the application is limited in the amount of data it can access.
With the GNU Compiler Suite, small memory model is
selected by invoking the compiler with either the
-msmall or -msmallmemoryXXX argument.
This argument must be included when linking the application
in order to ensure that support libraries also compiled
for the large memory model are used.
The default memory model is XXX.
When this memory model is selected, the XXX
symbol is predefined by the C and C++ compilers
and the XXX symbol is predefined by the assembler.
This behavior is the same for the GNU and Texas Instruments
toolsets. RTEMS uses these predefines to determine the proper handling
of the dp register in those C3x/C4x specific routines
that were written in assembly language.
RTEMS CPU Architecture Supplement
Copyright © 1988-2004 OAR Corporation