概 述
#if defined ( __CC_ARM )#define __ASM __asm /*!< asm keyword for ARM Compiler */#define __INLINE __inline /*!< inline keyword for ARM Compiler */#define __STATIC_INLINE static __inline#elif defined ( __GNUC__ )#define __ASM __asm /*!< asm keyword for GNU Compiler */#define __INLINE inline /*!< inline keyword for GNU Compiler */#define __STATIC_INLINE static inline#elif defined ( __ICCARM__ )#define __ASM __asm /*!< asm keyword for IAR Compiler */#define __INLINE inline /*!< inline keyword for IAR Compiler. Only available in High optimization mode! */#define __STATIC_INLINE static inline#elif defined ( __TMS470__ )#define __ASM __asm /*!< asm keyword for TI CCS Compiler */#define __STATIC_INLINE static inline#elif defined ( __TASKING__ )#define __ASM __asm /*!< asm keyword for TASKING Compiler */#define __INLINE inline /*!< inline keyword for TASKING Compiler */#define __STATIC_INLINE static inline#elif defined ( __CSMC__ )#define __packed#define __ASM _asm /*!< asm keyword for COSMIC Compiler */#define __INLINE inline /*use -pc99 on compile line !< inline keyword for COSMIC Compiler */#define __STATIC_INLINE static inline#endif
如果你写过Keil C51，你还会发现有如下（通过预处理）嵌套汇编：
#pragma asm; Assembler Code Here#pragma endasm
所以，你会发现，不同的编译器，汇编代码还是有差异。当然，这里主要是说C中嵌套汇编与编译器有关。
C中嵌套汇编代码
__ASM uint32_t __get_PSP(void){mrs r0, pspbx lr}
uint32_t __get_PSP(void){__ASM("mrs r0, psp");__ASM("bx lr");}
举 例
static portFORCE_INLINE void vPortRaiseBASEPRI( void ){uint32_t ulNewBASEPRI = configMAX_SYSCALL_INTERRUPT_PRIORITY;__asm{/* Set BASEPRI to the max syscall priority to effect a critical section. */msr basepri, ulNewBASEPRIdsbisb}}
2、FreeRTOS中port.c文件下源代码：
__asm void xPortPendSVHandler( void ){extern uxCriticalNesting;extern pxCurrentTCB;extern vTaskSwitchContext;PRESERVE8mrs r0, pspisbldr r3, =pxCurrentTCB /* Get the location of the current TCB. */ldr r2, [r3]stmdb r0!, {r4-r11} /* Save the remaining registers. */str r0, [r2] /* Save the new top of stack into the first member of the TCB. */stmdb sp!, {r3, r14}mov r0, #configMAX_SYSCALL_INTERRUPT_PRIORITYmsr basepri, r0dsbisbbl vTaskSwitchContextmov r0, #0msr basepri, r0ldmia sp!, {r3, r14}ldr r1, [r3]ldr r0, [r1] /* The first item in pxCurrentTCB is the task top of stack. */ldmia r0!, {r4-r11} /* Pop the registers and the critical nesting count. */msr psp, r0isbbx r14nop}
这是昨天分享过的一篇文章《一文弄懂STM32复位来源，以及系统与内核复位的区别》中的代码：
__asm void NVIC_CoreReset_a(void){LDR R0, =0xE000ED0CLDR R1, =0x05FA0001STR R1, [R0]deadloop_CoreB deadloop_Core}
END
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