Microchip AT32UC3C0256C Manual


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AVR Assembler
AVR Assembler
Preface
Welcome to the Microchip AVR® Assembler.
The Assembler generates fixed code allocations, consequently no linking is necessary.
The AVR Assembler is the assembler formerly known as AVR Assembler 2 (AVRASM2). The former
AVRASM distributed with AVR Studio® 4 has now been obsoleted and will not be distributed with current
products.
For documentation on the instruction set of the AVR family of microcontrollers, refer to the 8-bit AVR
Instruction Set Manual.
© 2017 Microchip Technology Inc. User Guide DS40001917A-page 1
In this example FOO is not defined at the point it is used in a conditional. The use of .ifdef in this situation
is allowed, and the conditional is false. However, the pattern shown above is not recommended because
the programmer's intention is not clear. The form is intended to allow common constructs like this:
; Define FOO if it is not already defined.
.ifndef FOO
.equ FOO = 0x100
.endif
Up to and including AVRASM 2.0.30, these situations were not always properly detected, causing
incomprehensible error messages. Starting with 2.0.31, explicit error messages are given.
Note that with preprocessor conditionals ( ), the situation is always well-defined,#if/#ifdef
preprocessor symbols are always undefined until the definition is seen, and this kind of error will never
occur.
Error messages
Sometimes error messages may be hard to understand. Typically, a simple typo in some instances may
produce error messages like this:
myfile.asm(30): error: syntax error, unexpected FOO
where FOO represents some incomprehensible gibberish. The referenced filename/line number is
correct, however.
defined incorrectly treated as an assembler keyword
The keyword is recognized in all contexts. It should only be recognized in conditionals. Thisdefined
prevents to be used as a user symbol like a label, etc. On the other hand, it allows for constructsdefined
like '.dw foo = defined(bar)', which it shouldn't. Note that the preprocessor and assembler have separate
implementations of . The exact behavior of currently (from 2.1.5) is:defined defined
The preprocessor 'defined' keyword only relates to symbols defined with , and correctly#define
does this only in preprocessor conditionals ( ).#if/#elif
In all remaining code, the assembler's notion of is used, the correct behavior would be todefined
only recognize it in assembler conditionals ( )..if/.elif
Preprocessor issues
The preprocessor will not detect invalid preprocessor directives inside a false conditional. This may
lead to surprises with typos like this:
#if __ATmega8__
//...
#elseif __ATmega16__ //WRONG, the correct directive is #elif
// This will go undetected if __ATmega8__ is false
//...
#else
// when __ATmega8__ is false this section will be assembled even if
// __ATmega16__ is true.
#endif
It is debatable if this is a bug, the behavior is consistent with the C preprocessor.
Issue #3361: The preprocessor incorrectly allows additional text after directives, which may cause
surprises, e.g., #endif #endif will be interpreted as a single #endif directive, without any error or
warning message.
AVR Assembler
© 2017 Microchip Technology Inc. User Guide DS40001917A-page 5


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Mærke: Microchip
Kategori: Ikke kategoriseret
Model: AT32UC3C0256C

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