 C166 User's Guide | |
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C166 User's Guide
C166 Introduction Compiling Programs Language Extensions Preprocessor Advanced Programming Sections, Classes, and Groups
Special Sections Locating Sections Customization Files Startup Code STARTUP.A66 START167.A66 Basic I/O Memory Allocation TRAPS.C Optimizer Optimizer Options General Optimizations 80C166-Specific Optimizations Global Register Coloring DPP Registers Stacks System Stack User Stack Stack Sizes System Stack Size User Stack Size XBUS Memory and Peripherals On-chip XRAM XBUS Peripherals Interfacing C to Assembler Function Parameters Function Return Values Using the SRC Directive Register Usage Example Routines TINY Model SMALL Model COMPACT Model MEDIUM Model LARGE Model Data Storage Formats Bit Variables 1-byte Scalars 2-byte Scalars 4-byte Scalars float Scalars float Errors double Scalars double Errors near Pointers far Pointers huge Pointers xhuge Pointers Absolute Memory Access Absolute Access Macros Linker Location Controls Debugging Error Messages Library Reference AppendixInterfacing C to Assembler
You can easily interface your C programs to routines written in XC16x/C16x/ST10 assembly language. The A166 Assembler is a macro assembler that emits object modules in OMF166 format. By following a few programming rules, you can call assembly routines from C and vice versa. Public variables declared in the assembly module are available to your C programs.
There are several reasons to call an assembly routine from your C program.
- You have assembly code already written that you wish to use.
- You need to improve the speed of a particular function.
- You want to manipulate SFRs or memory-mapped I/O devices directly from assembly.
This section describes how to write assembly routines that can be directly interfaced to C programs.
For an assembly routine to be called from C, it must be aware of the parameter passing and return value conventions used in C functions. For all practical purposes, the assembly routine must appear to be a C function.
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