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Cx51 User's Guide
Cx51 Introduction Compiling Programs Language Extensions Preprocessor Advanced Programming Customization Files
Startup Code Variable Initialization Code XBANKING.A51 Basic I/O Memory Allocation Optimizer Optimizer Options General Optimizations 8051-Specific Optimizations Global Register Coloring Segment Naming Conventions Data Objects Program Objects Parameters and Local Variables Interfacing C to Assembler Global Variables Function Parameters Passing in Memory Passing in Registers Function Return Values Using the SRC Directive Register Usage Overlaying Segments Small Model Example Compact Model Example Large Model Example Interfacing C programs to PL/M-51 Data Storage Formats Bit Variables 1-Byte Scalars 2-Byte Scalars 4-Byte Scalars Generic and Far Pointers Floating-point Numbers Floating-point Errors Absolute Memory Locations Absolute Access Macros Linker Location Controls The _at_ Keyword Debugging 8051 Derivatives Error Messages Library Reference AppendixOverlaying Segments
If the overlay process is executed during program linking and locating, it is important that each assembler subroutine have a unique program segment. This is necessary so that during the overlay process, the references between the functions are calculated, using the references of the individual segments.
The data areas of the assembler subprograms may be included in the overlay analysis when the following points are observed:
- All segment names must be created using the Cx51 Compiler segment naming conventions.
- Each assembler function with local variables must be assigned its own data segment. This data segment may be accessed by other functions only for passing parameters. Parameters must be passed in order.
The following C functions are used in all of these examples:
int function ( int v_a, /* passed in R6 & R7 */ char v_b, /* passed in R5 */ bit v_c, /* passed in fixed memory location */ long v_d, /* passed in fixed memory location */ bit v_e); /* passed in fixed memory location */
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