| ||||
| Home Products Download Events Support | ||||
Technical Support
On-Line Manuals
C166 User's Guide
C166 Introduction Compiling Programs 
Language Extensions 
Keywords Memory Models Tiny Model Small Model Medium Model Compact Model Large Model HCompact Model HLarge Model XLarge Model Memory Types near far bdata ebdata idata sdata huge xhuge Memory Type Comparison Pointers with Memory Types Implicit Memory Types Type Qualifiers const volatile Data Types Special Function Registers sfr Types sbit Types bit Types Bit-Addressable Objects Function Declarations Return Values Register Bank Register Mask Interrupt Functions Fast Interrupts Cached Vectors Fast Register Banks Inline Functions Real-Time Function Tasks Inline Assembly Traditional Inline Assembly Extended Inline Assembly Operands Operators Register Use Use in Macro Definitions Preprocessor Advanced Programming Error Messages Library Reference AppendixRegister Mask
The C166 Compiler supports register masks for function prototypes and external function declarations. The register mask specifies which registers are modified by the function. The register mask is used by the compiler to optimize registers used in the code generated.
The following example shows the definition of a register mask:
<[>extern<]> <[>type<]> funcname (<[>args<]>) @mask
The reg_mask is a 16-bit number that specifies the register modified by this function. Each bit in the reg_mask refers to one C16x/ST10 register. The encoding is as follows:
| Bit Position | |||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 15 | 14 | 13 | 12 | 11 | 10 | 9 | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
| -- | DPP3 | MDx | R12 | R11 | R10 | R9 | R8 | R7 | R6 | R5 | R4 | R3 | R2 | R1 | DPP0 |
- DPP3 is the DPP3 register used in copy and compare functions for memory images and strings.
- MDx is the MDL, MDH, and MDC register which is used for multiplication and division.
- R1-R12 are the registers R1-R12. R13, R14, and R15 are saved by the called function and the saved contents are never altered for the caller.
- DPP0 is the DPP0 register that is used for far, huge, and xhuge accesses.
Two special values of the register mask specify all register or no registers:
- 0 (zero) specifies that the function uses all registers. This is the default if the function prototype does not specify a register mask.
- 0x8000 specifies that the function uses no registers. This value is useful for functions like exit that never return to the caller.
The C166 Compiler displays the register mask for each function in the assembly listing (generated by the CODE directive) included in the listing file. The register mask (RMASK) is printed at the beginning and at the end of the function.
Note
- Register mask specifications assist the compiler in generating code with calls to external functions or with forward calls to functions. They are only included for backwards compatibility with C166 Version 1 programs and should not be used for new projects.
- Register masks are provided for compatibility with C166 Version 1 programs. Use the REGFILE compiler directive and REGFILE linker directive to enable global register optimization which automatically creates register masks definitions.
| Contact Site Map Press Privacy | Copyright © 2012 ARM Ltd and ARM Germany GmbH. All rights reserved. |
