内嵌汇编

(仅做了解)

__asm volatile (

                  汇编语句模板：

                  输出部分：

                  输入部分：

                  破坏描述部分

                  ）; 内嵌汇编允许我们在C或C++代码中插入汇编代码，并且不需要我们安装额外的汇编语言编译器

用法

实现c/c++无法实现的操作,比如FreeRTOS的上下文切换

void  vPortSVCHandler( void )
{
    __asm volatile (
        " ldr r3, pxCurrentTCBConst2 \n"/* Restore the context. */
        " ldr r1, [r3] \n"/* Use pxCurrentTCBConst to get the pxCurrentTCB address. */
        " ldr r0, [r1] \n"/* The first item in pxCurrentTCB is the task top of stack. */
        " ldmia r0!, {r4-r11} \n"/* Pop the registers that are not automatically saved on exception entry and the critical nesting count. */
        " msr psp, r0 \n"/* Restore the task stack pointer. */
        " isb \n"
        " mov r0, #0 \n"
        " msr basepri, r0 \n"
        " orr r14, #0xd \n"
        " bx r14 \n"
        " \n"
        " .align 4 \n"
        "pxCurrentTCBConst2: .word pxCurrentTCB \n"
    );
}

或者运行发生致命错误，C语言的运行环境可能已经不存在，需要恢复运行现场

void  HardFault_Handler(void) {
    __asm volatile(
        " tst lr, #4 \n"
        " ite eq \n"
        " mrseq r0, msp \n"
        " mrsne r0, psp \n"
        " ldr r1, [r0, #24] \n"
        " ldr r2, handler2_address_const \n"
        " bx r2 \n"
        " handler2_address_const: .word GetRegistersFromStack \n");
}