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CARM User's Guide
CARM Introduction Compiling Programs Language Extensions Preprocessor Advanced Programming Customization Files
Startup Code Basic I/O Memory Allocation Interfacing C to Assembler Function Parameters Function Return Values Using the SRC Directive Register Usage Example Routines ARM Code Example Thumb Code Example Data Storage Formats Byte Order Byte Alignment Integer Scalars 1-Byte Scalars 2-Byte Scalars 4-Byte Scalars 8-Byte Scalars float Scalars float Format float Errors double Scalars double Format double Errors Pointers Bit Fields Absolute Memory Access The __at Keyword Linker Location Controls Error Messages Library Reference AppendixRegister Usage
Assembler functions may destroy the contents of R0-R3, R8-R12, and R14. When invoking a C function from assembly, you must assume that these registers are destroyed.
Registers R4-R7 may be used but their contents must be saved (on entry) and restored (before returning).
The following registers have special meaning and must be preserved by all assembler routines.
| Register | Description |
|---|---|
| R13 = SP | R13 is the stack pointer. |
| R14 = LR | R14 is the link register that holds the function return value. It may be destroyed by the assembly function. |
| R15 = PC | R15 may be used but its contents must be saved (on entry) and restored (before returning). |
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