ARM Compiler toolchain v4.1 for µVision Using the Compiler

Using the Inline and Embedded Assemblers of the ARM Compiler
7.8 Inline assembler register restrictions in C and C++ code
Registers such as r0-r3, sp, lr, and the NZCV flags in the CPSR must be used with caution. If C
or C++ expressions are used, these might be used as temporary registers and NZCV flags might
be corrupted by the compiler when evaluating the expression.
The pc, lr, and sp registers cannot be explicitly read or modified using inline assembly code
because there is no direct access to any physical registers. However, the intrinsics __current_pc,
__current_sp, and __return_address can be used to read these registers.
7.8.1 See also
Concepts
• Inline assembler and register access in C and C++ code on page 7-18
• Restrictions on inline assembly operations in C and C++ code on page 7-11.
Reference
Compiler Reference:
• __current_pc intrinsic on page 5-63
• __current_sp intrinsic on page 5-64
• __return_address intrinsic on page 5-77.
ARM DUI 0375C Copyright © 2007-2008, 2011 ARM. All rights reserved. 7-12
ID061811
Non-Confidential