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! Trigraphs |
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C51 now supports trigraph sequences. |
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! Variable-length Argument Lists for All Functions |
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Variable-length argument lists are now supported for all function types. |
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Functions with a variable length argument list do not have to be declared |
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using the reentrant attribute. The new command line directive MAXARGS |
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determines the size of the parameter passing area. |
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Version 3.0 Differences |
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!New Control Directive Added for Assembly Source File Output
The SRC control directive has been added to direct the compiler to generate an assembly language source file instead of an object file.
!New Library Functions
The library functions calloc, free, init_mempool, malloc, and realloc have been added.
318 Appendix B. Version Differences
Version 2 Differences
! Absolute Register Addressing
C51 now generates code that performs absolute register addressing. This improves execution speed. The control directives AREGS and NOAREGS, respectively, enable or disable this feature.
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Bit-addressable Memory Type |
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Variable types of char and int can now be declared to reside in the |
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bit-addressable internal memory area by using the bdata memory specifier. |
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Intrinsic Functions |
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Intrinsic functions have been added to the library to support some of the |
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special instructions built in to the 8051. |
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Mixed Memory Models |
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Calls to and from functions of different memory models are now supported. |
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New Optimizer Levels |
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Two new levels of optimization have been added to the C51 compiler. These |
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new levels support register variables, local common subexpression |
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elimination, loop optimizations, and global common subexpression |
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elimination, to name a few. |
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New Predefined Macros |
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The macros _ _C51_ _ and _ _MODEL_ _ are now defined by the |
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preprocessor at compile time. |
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! Reentrant and Recursive Functions |
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Individual functions may now be defined as being reentrant or recursive by |
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using the reentrant function attribute. |
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! Registers Used for Parameter Passing |
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C51 now passes up to 3 function arguments using registers. The |
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REGPARMS and NOREGPARMS directives enable or disable this feature. |
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! Support for Memory-specific Pointers |
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Pointers may now be defined to reference data in a particular memory area. |
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! Support for PL/M-51 Functions |
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The alien keyword has been added to support PL/M-51 compatible functions |
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and function calls. |
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Volatile Type Specifier |
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The volatile variable attribute may be used to enforce variable access and to |
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prevent optimizations involving that variable. |
Keil Software — C51 Compiler User’s Guide |
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Using C51 Version 5 with Previous
Versions
You may wish to use the C51 Version 5 with older versions of the 8051 development tools such as BL51, OHS51, or debugging tools and emulators. The new compiler adds object file records for register optimization which makes
the object format incompatible with the old tools. However, you can direct the B compiler and linker to generate object modules that are compatible with the old
tools.
1.Invoke C51 with the control NOAMAKE and do not use REGFILE. or
2.Invoke L51 or BL51 with the control NOAMAKE.
If you are using old debugging tools, you may have problems displaying floating-point numbers and pointers. Make sure that you have current versions of the debugging software.
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Appendix B. Version Differences |
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