Version 3.4 Differences

_at_Keyword

C51 supports variable location using the _at_ keyword. This new keyword allows you to specify the address of a variable in a declaration. Refer to “The _at_ Keyword” on page 186 for more information.

OH51 Hex File Converter

The OHS51 Object-Hex-Symbol Converter provided with prior versions of C51 has been replaced with OH51.

Optimizer Level 6

C51 now supports optimizer level 6 which provides loop rotation. The resulting code is more efficient and executes faster.

ORDER Directive

When you specify the ORDER directive, C51 locates variables in memory in the order in which they are declared in your source file. Refer to “ORDER” on page 65 for more information.

REGFILE Directive

C51 now supports the REGFILE directive which lets you specify the name of the register definition file generated by the linker. This file contains information that is used to optimize the use of registers between functions in different modules. Refer to “REGFILE” on page 70 for more information.

vprintf and vsprint Library Functions

The vprintf and vsprintf library functions have been added. Refer to “vprintf” on page 349 and “vsprintf” on page 351 for more information.

Version 3.2 Differences

ANSI Standard Automatic Integer Promotion

The latest version of the ANSI C Standard requires that calculations use int values if char or unsigned char values might overflow during the

calculation. This new requirement is based on the premise that int and char operations are similar on 16-bit CPUs. C51 supports this feature as the

B default and provides you with two new directives, INTPROMOTE and NOINTPROMOTE, to enable or disable integer promotion.

There is a big difference between 8-bit and 16-bit operations on the 8-bit 8051 in terms of code size and execution speed. For this reason, you might want to disable integer promotion by using the NOINTPROMOTE directive.

However, if you wish to retain maximum compatibility with other C compilers and platforms, leave integer promotions enabled.

Assembly Source Generation with In-Line Assembly

You may use the new directives ASM and ENDASM to include source text to output to .SRC files generated using the SRC command directive.

New Directives

The directives ASM, ENDASM, INTERVAL, INTPROMOTE, INTVECTOR, MAXARGS, and NOINTPROMOTE have been added or enhanced.

Offset and Interval Can Now Be Specified for Interrupt Vectors

You may now specify the offset and interval for the interrupt vector table. These features provide support for the SIECO-51 derivatives and allow you to specify a different location for the interrupt vector in situations where the interrupt table is not located at address 0000h.

Parameter Passing to Indirectly Called Functions

Function parameters may now be passed to indirectly called functions if all of the parameters can be passed in CPU registers. These functions do not have to be declared with the reentrant attribute.

Source Code Provided For Memory Allocation Functions

C source code for the memory allocation routines is now provided with the C51 compiler. You may now more easily adapt these functions to the hardware architecture of your embedded system.

Trigraphs

C51 now supports trigraph sequences.

Variable-length Argument Lists for All Functions

Variable-length argument lists are now supported for all function types. Functions with a variable length argument list do not have to be declared using the reentrant attribute. The new command line directive MAXARGS determines the size of the parameter passing area.

364 Appendix B. Version Differences

Version 2 Differences

B