CMSIS-Core (Cortex-M): Compiler Control

| CMSIS-Core (Cortex-M) Version 5.3.0 CMSIS-Core support for Cortex-M processor-based devices

- Main Page
- Usage and Description
- Reference

All Data Structures Files Functions Variables Enumerations Enumerator Groups Pages
Macros
Compiler Control

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

## Macros
#define | __ARM_ARCH_6M__
| Set to 1 when generating code for Armv6-M (Cortex-M0, Cortex-M1) More...
#define | __ARM_ARCH_7M__
| Set to 1 when generating code for Armv7-M (Cortex-M3) More...
#define | __ARM_ARCH_7EM__
| Set to 1 when generating code for Armv7-M (Cortex-M4) with FPU. More...
#define | __ARM_ARCH_8M_BASE__
| Set to 1 when generating code for Armv8-M Baseline. More...
#define | __ARM_ARCH_8M_MAIN__
| Set to 1 when generating code for Armv8-M Mainline. More...
#define | __ASM
| Pass information from the compiler to the assembler. More...
#define | __INLINE
| Recommend that function should be inlined by the compiler. More...
#define | __STATIC_INLINE
| Define a static function that may be inlined by the compiler. More...
#define | __STATIC_FORCEINLINE
| Define a static function that should be always inlined by the compiler. More...
#define | __NO_RETURN
| Inform the compiler that a function does not return. More...
#define | __RESTRICT
| restrict pointer qualifier to enable additional optimizations. More...
#define | __USED
| Inform that a variable shall be retained in executable image. More...
#define | __WEAK
| Export a function or variable weakly to allow overwrites. More...
#define | __PACKED
| Request smallest possible alignment. More...
#define | __PACKED_STRUCT
| Request smallest possible alignment for a structure. More...
#define | __UNALIGNED_UINT32
| Pointer for unaligned access of a uint32_t variable. More...
#define | __UNALIGNED_UINT16_READ
| Pointer for unaligned read of a uint16_t variable. More...
#define | __UNALIGNED_UINT16_WRITE
| Pointer for unaligned write of a uint16_t variable. More...
#define | __UNALIGNED_UINT32_READ
| Pointer for unaligned read of a uint32_t variable. More...
#define | __UNALIGNED_UINT32_WRITE
| Pointer for unaligned write of a uint32_t variable. More...
#define | __ALIGNED
| Minimum alignment for a variable. More...
#define | __COMPILER_BARRIER
| Barrier to prevent compiler from reordering instructions. More...
#define | __PROGRAM_START
| Entry function into the user application or library startup. More...
#define | __INITIAL_SP
| Compiler/linker symbol specifiying the location of the main stack (MSP). More...
#define | __STACK_LIMIT
| Compiler/linker symbol specifiying the limit of the main stack (MSP). More...
#define | __VECTOR_TABLE
| Symbol name used for the (static) interrupt vector table. More...
#define | __VECTOR_TABLE_ATTRIBUTE
| Additional decl specs to be used when defining the (static) interrupt vector table. More...

## Description

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

The header file cmsis_compiler.h is also included by each Device Header File <device.h> so that these definitions are available.

## Macro Definition Documentation

#define __ALIGNED

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_6M__

The #define ARM_ARCH_6M is set to 1 when generating code for the Armv6-M architecture. This architecture is for example used by the Cortex-M0, Cortex-M0+, and Cortex-M1 processor.

#define __ARM_ARCH_7EM__

The #define ARM_ARCH_7EM is set to 1 when generating code for the Armv7-M architecture with floating point extension. This architecture is for example used by the Cortex-M4 processor with FPU

#define __ARM_ARCH_7M__

The #define ARM_ARCH_7M is set to 1 when generating code for the Armv7-M architecture. This architecture is for example used by the Cortex-M3 processor.

#define __ARM_ARCH_8M_BASE__

The #define ARM_ARCH_8M_BASE is set to 1 when generating code for the Armv8-M architecture baseline variant.

#define __ARM_ARCH_8M_MAIN__

The #define ARM_ARCH_8M_MAIN is set to 1 when generating code for the Armv8-M architecture mainline variant.

#define __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 __COMPILER_BARRIER

This barrier limits the compilers reordering optimizations. It prevents the compiler from swapping instructions resulting from code before and after the barrier.

Code Example: The assignments in the example are independent. Hence the compiler could choose a different order of execution, e.g. for a better pipeline utilization. Using the barrier in between prevents this type of reordering.

void test (uint8_t *ptr) {
var1 = 1;
__COMPILE_BARRIER();
var2 = var3 + 1;
}

#define __INITIAL_SP

The address of the specified symbol is used to initialize the main stack pointer (MSP) during low level init. This is compiler/linker specific. CMSIS specifies common default for supported compilers.

Note
  This define is only intended to be used by the Startup File startup_<device>.c.

#define __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

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

Specifies that a type must have the smallest possible alignment.

Code Example:

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

#define __PACKED_STRUCT

Specifies that a structure must have the smallest possible alignment.

Code Example:

__PACKED_STRUCT foo {
uint8_t u8;
uint32_t u32;
uint16_t u16;
};

#define __PROGRAM_START

Gives the function to be jumped into right after low level initialization, i.e. SystemInit. This is compiler and library specific. CMSIS specifies common default for supported compilers.

Note
  This define is only intended to be used by the Startup File startup_<device>.c.

Code Example:

void Reset_Handler(void)
{
SystemInit(); /* CMSIS System Initialization */
__PROGRAM_START(); /* Enter PreMain (C library entry point) */
}

#define __RESTRICT

The __RESTRICT keyword corresponds to the restrict pointer qualifier that has been introduced in C99. __RESTRICT is a hint to the compiler that enables additional optimizations. It specifies that for the lifetime of the pointer, only the pointer itself or a value directly derived from it (such as pointer + 1) is used to access the object. The compiler may therefore ignore potential pointer aliasing effects and perform additional optimizations.

Note
  For compilers that do not support the restrict keyword, __RESTRICT is defined as an empty macro and a warning is issued.

Code Example:

__STATIC_INLINE void ARM_MPU_OrderedMemcpy (volatile uint32_t* dst, const uint32_t* __RESTRICT src, uint32_t len)
{
uint32_t i;
for (i = 0U; i < len; ++i)
{
dst[i] = src[i]; // Since src is restrict, the compiler can assume that dst and src are not overlapping may load multiple values at a time
}
}

#define __STACK_LIMIT

The address of the specified symbol is used to initialize the main stack pointer limit (MSPLIM on Armv8-M) during low level init. This is compiler/linker specific. CMSIS specifies common default for supported compilers.

Note
  This define is only intended to be used by the Startup File startup_<device>.c.

Code Example:

void Reset_Handler(void)
{
__set_MSPLIM((uint32_t)(&__STACK_LIMIT));
// :
// :
}

#define __STATIC_FORCEINLINE

Defines a static function that should be always inlined by the compiler.

Note
  For compilers that do not allow to force function inlining, the macro maps to __STATIC_INLINE.

Code Example:

\\ Get Interrupt Vector
__STATIC_FORCEINLINE uint32_t NVIC_GetVector(IRQn_Type IRQn)
{
uint32_t *vectors = (uint32_t *)SCB->VTOR;
return vectors[(int32_t)IRQn + NVIC_USER_IRQ_OFFSET];
}

#define __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:

\\ Get Interrupt Vector
__STATIC_INLINE uint32_t NVIC_GetVector(IRQn_Type IRQn)
{
uint32_t *vectors = (uint32_t *)SCB->VTOR;
return vectors[(int32_t)IRQn + NVIC_USER_IRQ_OFFSET];
}

#define __UNALIGNED_UINT16_READ

Defines a pointer to a uint16_t from an address that does not need to be aligned. This can then be used in read operations. The compiler will generate the appropriate access (aligned or non-aligned) depending on the underlying Arm processor core and compiler settings.

Code Example:

uint16_t val16;
void test (uint8_t *ptr) {
val16 = __UNALIGNED_UINT16_READ(ptr);
}

#define __UNALIGNED_UINT16_WRITE

Defines a pointer to a uint16_t from an address that does not need to be aligned. This can then be used in write operations. The compiler will generate the appropriate access (aligned or non-aligned) depending on the underlying Arm processor core and compiler settings.

Code Example:

uint16_t val16 = 0U;
void test (uint8_t *ptr) {
__UNALIGNED_UINT16_WRITE(ptr, val16);
}

#define __UNALIGNED_UINT32

Deprecated:
  Do not use this macro. It has been superseded by __UNALIGNED_UINT32_READ, __UNALIGNED_UINT32_WRITE and will be removed in the future.

Defines a pointer to a uint32_t from an address that does not need to be aligned. This can then be used in read/write operations. The compiler will generate the appropriate access (aligned or non-aligned) depending on the underlying Arm processor core and compiler settings.

Code Example:

uint32_t val32;
void test (uint8_t *ptr) {
__UNALIGNED_UINT32(ptr) = val32;
}

#define __UNALIGNED_UINT32_READ

Defines a pointer to a uint32_t from an address that does not need to be aligned. This can then be used in read operations. The compiler will generate the appropriate access (aligned or non-aligned) depending on the underlying Arm processor core and compiler settings.

Code Example:

uint32_t val32;
void test (uint8_t *ptr) {
val32 = __UNALIGNED_UINT32_READ(ptr);
}

#define __UNALIGNED_UINT32_WRITE

Defines a pointer to a uint32_t from an address that does not need to be aligned. This can then be used in write operations. The compiler will generate the appropriate access (aligned or non-aligned) depending on the underlying Arm processor core and compiler settings.

Code Example:

uint32_t val32 = 0U;
void test (uint8_t *ptr) {
__UNALIGNED_UINT32_WRITE(ptr, val32);
}

#define __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 __VECTOR_TABLE

The given name is used for defining the static (compiler time) interrupt vector table. The name must comply with any compiler/linker conventions, e.g. if used for vector table relocation or debugger awareness. CMSIS specifies common default for supported compilers.

Note
  This define is only intended to be used by the Startup File startup_<device>.c.

#define __VECTOR_TABLE_ATTRIBUTE

The given decl specs are used for defining the static (compiler time) interrupt vector table, e.g. to mark the table as used and force it into a specific linker section. CMSIS specifies common default for supported compilers.

Note
  This define is only intended to be used by the Startup File startup_<device>.c.

#define __WEAK

Functions defined with __WEAK export their symbols weakly. A weakly defined function behaves like a normally defined function unless a non-weakly defined function of the same name is linked into the same image. If both a non-weakly defined function and a weakly defined function exist in the same image then all calls to the function resolve to call 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();
}