ARM Compiler toolchain v4.1 for µVision Using the Compiler

Using the Inline and Embedded Assemblers of the ARM Compiler
7.10 Inline assembler Thumb instruction set restrictions in C and C++ code
The inline assembler is not available when compiling C or C++ for Thumb state, and the inline
assembler does not assemble Thumb instructions. Instead, the compiler switches to ARM state
automatically.
Inline assembly language can be included in a source file that contains code to be compiled for
Thumb, by enclosing the functions containing inline assembler code between #pragma arm and
#pragma thumb statements. For example:
... // Thumb code
#pragma arm // ARM code. Switch code generation to the ARM instruction set so
// that the inline assembler is available.
int add(int i, int j)
{
int res;
__asm
{
ADD res, i, j // add here
}
return res;
}
#pragma thumb
// Thumb code. Switch back to the Thumb instruction set.
// The inline assembler is no longer available.
The code must also be compiled using the --apcs /interwork compiler command-line option.
7.10.1 See also
Concepts
• Restrictions on inline assembly operations in C and C++ code on page 7-11.
Reference
Compiler Reference:
• --apcs=qualifer...qualifier on page 3-7
• Pragmas on page 5-47.
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