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RealView Compiler Reference Guide

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RealView Compiler Reference Guide

Preface
Introduction
Compiler Command-line Options
Language Extensions
Compiler-specific Features
Keywords and operators
__align
__alignof__
__ALIGNOF__
__asm
__forceinline
__global_reg
__inline
__int64
__INTADDR__
__irq
__packed
__pure
__smc
__softfp
__svc
__svc_indirect
__svc_indirect_r7
__value_in_regs
__weak
__writeonly
__declspec attributes
__declspec(dllexport)
__declspec(dllimport)
__declspec(noinline)
__declspec(noreturn)
__declspec(nothrow)
__declspec(notshared)
__declspec(thread)
Function attributes
__attribute__((alias))
__attribute__((always_inline))
__attribute__((const))
__attribute__((deprecated))
__attribute__((malloc))
__attribute__((noinline))
__attribute__((noreturn))
__attribute__((pure))
__attribute__((section))
__attribute__((unused))
__attribute__((used))
__attribute__((weak))
Type attributes
__attribute__((aligned))
__attribute((packed))
__attribute__((transparent_union))
Variable attributes
__attribute__((alias))
__attribute__((at(address)))
__attribute__((aligned))
__attribute__((deprecated))
__attribute__((packed))
__attribute__((section))
__attribute__((transparent_union))
__attribute__((unused))
__attribute__((used))
__attribute__((weak))
__attribute__((zero_init))
Pragmas
#pragma [no_]anon_unions
#pragma arm
#pragma arm section [section_sort_list]
#pragma diag_default tag[,tag,...]
#pragma diag_error tag[,tag,...]
#pragma diag_remark tag[,tag,...]
#pragma diag_suppress tag[,tag,...]
#pragma diag_warning tag[, tag, ...]
#pragma [no_]exceptions_unwind
#pragma hdrstop
#pragma import symbol_name
#pragma [no_]inline
#pragma no_pch
#pragma Onum
#pragma once
#pragma Ospace
#pragma Otime
#pragma pop
#pragma push
#pragma [no_]softfp_linkage
#pragma unroll [(n)]
#pragma unroll_completely
#pragma thumb
Instruction intrinsics
__breakpoint
__builtin_clz
__builtin_constant_p
__builtin_expect
__builtin_frame_address
__builtin_return_address
__builtin_popcount
__cdp
__clrex
__clz
__current_pc
__current_sp
__disable_fiq
__disable_irq
__enable_fiq
__enable_irq
__fabs
__fabsf
__force_stores
__ldrex
__ldrt
__memory_changed
__nop
__pld
__pli
__qadd
__qdbl
__qsub
__rbit
__rev
__return_address
__ror
__schedule_barrier
__semihost
__sev
__sqrt
__sqrtf
__ssat
__strex
__strt
__swp
__usat
__wfe
__wfi
__yield
ARMv6 SIMD intrinsics
ETSI basic operations
C55x intrinsics
Named register variables
Compiler predefines
Predefined macros
Function names
C and C++ Implementation Details
Via File Syntax
Standard C Implementation Definition
Standard C++ Implementation Definition
C and C++ Compiler Implementation Limits

__ldrex

4.7.20. __ldrex

This intrinsic inserts an instruction of the form LDREX{size} into the instruction stream generated by the compiler. It enables you to load data from memory in your C or C++ code using an LDREX instruction.

Syntax

unsigned int __ldrex(volatile void *ptr)

Where:

ptr

Points to the address of the data to be loaded from memory. To specify the size of the data to be loaded, cast the parameter to an appropriate integral type.

Table 4.8. Access widths supported by the __ldrex intrinsic

InstructionSize of data loadedC cast
LDREXBunsigned byte(char *)
LDREXHunsigned halfword(short int *)
LDREXword(int *)

Return value

The __ldrex intrinsic returns the data loaded from the memory address pointed to by ptr.

Errors

The compiler does not recognize the __ldrex intrinsic when compiling for a target that does not support the LDREX instruction. The compiler generates either a warning or an error in this case.

The __ldrex intrinsic does not support access to doubleword data. The compiler generates an error if you specify an access width that is not supported.

Example

int foo(void)
{
    int loc = 0xff;
    return __ldrex((volatile char *)loc);
}

Compiling this code with the command‑line option --device=DLM produces

||foo|| PROC
        MOVS     r0,#0xff
        LDREXB   r0,[r0]
        BX       lr
        ENDP

See also

Copyright © 2007 ARM Limited. All rights reserved.ARM DUI 0376A