CMSIS-Core (Cortex-A): Compiler Control

| CMSIS-Core (Cortex-A) Version 1.0.0 CMSIS-Core support for Cortex-A processor-based devices

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Macros
Compiler Control

Compiler agnostic #define symbols for generic C/C++ source code. More...

## Macros
#define | __ARM_ARCH_7A__ 1
| Set to 1 when generating code for ARMv7-A (Cortex-A7) More...
#define | __ASM __asm
| Pass information from the compiler to the assembler. More...
#define | __INLINE __inline
| Recommend that function should be inlined by the compiler. More...
#define | __STATIC_INLINE static __inline
| Define a static function should be inlined by the compiler. More...
#define | __NO_RETURN __declspec(noreturn)
| Inform the compiler that a function does not return. More...
#define | __USED __attribute__((used))
| Inform that a variable shall be retained in executable image. More...
#define | __WEAK __attribute__((weak))
| Export a function or variable weakly to allow overwrites. More...
#define | __ALIGNED(x) __attribute__((aligned(x)))
| Minimum alignment for a variable. More...
#define | __PACKED __attribute__((packed))
| Request smallest possible alignment. More...

## Description

The CMSIS-Core provides the header file cmsis_compiler.h with consistent #define symbols to generate C or C++ source files that should be compiler agnostic. Each CMSIS compliant compiler should support the functionality described in this section.

## Macro Definition Documentation

#define __ALIGNED | ( |  | x | ) | __attribute__((aligned(x)))

Specifies a minimum alignment for a variable or structure field, measured in bytes.

Code Example:

uint32_t stack_space[0x100] __ALIGNED(8); // 8-byte alignment required

#define __ARM_ARCH_7A__ 1

The #define ARM_ARCH_7A is set to 1 when generating code for the ARMv7-A architecture. This architecture is for example used by the Cortex-A7 processor.

#define __ASM __asm

The __ASM keyword can declare or define an embedded assembly function or incorporate inline assembly into a function (shown in the code example below).

Code Example:

// Reverse bit order of value
__attribute__( ( always_inline ) ) __STATIC_INLINE uint32_t __RBIT(uint32_t value)
{
uint32_t result;
__ASM volatile ("rbit %0, %1" : "=r" (result) : "r" (value) );
return(result);
}

#define __INLINE __inline

Inline functions offer a trade-off between code size and performance. By default, the compiler decides during optimization whether to inline code or not. The __INLINE attribute gives the compiler an hint to inline this function. Still, the compiler may decide not to inline the function. As the function is global an callable function is also generated.

Code Example:

const uint32_t led_mask[] = {1U << 4, 1U << 5, 1U << 6, 1U << 7};
//------------------------------------------------------------------------------
// Switch on LEDs
//------------------------------------------------------------------------------
__INLINE static void LED_On (uint32_t led) {
PTD->PCOR = led_mask[led];
}

#define __NO_RETURN __declspec(noreturn)

Informs the compiler that the function does not return. The compiler can then perform optimizations by removing code that is never reached.

Code Example:

// OS idle demon (running when no other thread is ready to run).
__NO_RETURN void os_idle_demon (void);

#define __PACKED __attribute__((packed))

Specifies that a type must have the smallest possible alignment.

Code Example:

struct foo {
uint8_t u8;
uint32_t u32[2] __PACKED;
};

#define __STATIC_INLINE static __inline

Defines a static function that may be inlined by the compiler. If the compiler generates inline code for all calls to this functions, no additional function implementation is generated which may further optimize space.

Code Example:

__STATIC_INLINE uint32_t GIC_GetPriority(IRQn_Type IRQn)
{
return((uint32_t)GICDistributor->D_IPRIORITYR[((uint32_t)(int32_t)IRQn)]);
}

#define __USED __attribute__((used))

Definitions tagged with __USED in the source code should be not removed by the linker when detected as unused.

Code Example:

// Export following variables for debugging
__USED uint32_t const CMSIS_RTOS_API_Version = osCMSIS;
__USED uint32_t const CMSIS_RTOS_RTX_Version = osCMSIS_RTX;
__USED uint32_t const os_clockrate = OS_TICK;
__USED uint32_t const os_timernum = 0;

#define __WEAK __attribute__((weak))

Functions defined with __WEAK export their symbols weakly. A function defined weak behaves like a normal defined function unless a non-weak function with the same name is linked into the same image. If both a non-weak function and a weak defined function exist in the same image, then all calls to the function resolve to the non-weak function.

Functions declared with __WEAK and then defined without __WEAK behave as non-weak functions.

Code Example:

__WEAK void SystemInit(void)
{
SystemCoreSetup();
SystemCoreClockSetup();
}