找到freertos的上下文切换功能

Posted 2023-02-19

【中文标题】找到freertos的上下文切换功能

【英文标题】：Find the context switch function of freertos

【发布时间】：2021-12-22 09:13:19

【问题描述】：

我在具有 cortex-M7 架构的 STM32 中使用 freeRTOS CMSIS v1。我目前的目标是研究它并了解“幕后”机制（我为此目的使用调试器）。

我正在尝试使用“上下文切换”功能，但我无法到达那里。有可能达到吗？要查看源代码吗？

谢谢！！

【参考方案1】：

是一个异常处理程序（supervisor call handler）：

void xPortPendSVHandler( void )

    /* This is a naked function. */

    __asm volatile
    (
    "   mrs r0, psp                         \n"
    "   isb                                 \n"
    "                                       \n"
    "   ldr r3, pxCurrentTCBConst           \n" /* Get the location of the current TCB. */
    "   ldr r2, [r3]                        \n"
    "                                       \n"
    "   tst r14, #0x10                      \n" /* Is the task using the FPU context?  If so, push high vfp registers. */
    "   it eq                               \n"
    "   vstmdbeq r0!, s16-s31             \n"
    "                                       \n"
    "   stmdb r0!, r4-r11, r14            \n" /* Save the core registers. */
    "   str r0, [r2]                        \n" /* Save the new top of stack into the first member of the TCB. */
    "                                       \n"
    "   stmdb sp!, r0, r3                 \n"
    "   mov r0, %0                          \n"
    "   msr basepri, r0                     \n"
    "   dsb                                 \n"
    "   isb                                 \n"
    "   bl vTaskSwitchContext               \n"
    "   mov r0, #0                          \n"
    "   msr basepri, r0                     \n"
    "   ldmia sp!, r0, r3                 \n"
    "                                       \n"
    "   ldr r1, [r3]                        \n" /* The first item in pxCurrentTCB is the task top of stack. */
    "   ldr r0, [r1]                        \n"
    "                                       \n"
    "   ldmia r0!, r4-r11, r14            \n" /* Pop the core registers. */
    "                                       \n"
    "   tst r14, #0x10                      \n" /* Is the task using the FPU context?  If so, pop the high vfp registers too. */
    "   it eq                               \n"
    "   vldmiaeq r0!, s16-s31             \n"
    "                                       \n"
    "   msr psp, r0                         \n"
    "   isb                                 \n"
    "                                       \n"
    #ifdef WORKAROUND_PMU_CM001 /* XMC4000 specific errata workaround. */
        #if WORKAROUND_PMU_CM001 == 1
    "           push  r14                 \n"
    "           pop  pc                   \n"
        #endif
    #endif
    "                                       \n"
    "   bx r14                              \n"
    "                                       \n"
    "   .align 4                            \n"
    "pxCurrentTCBConst: .word pxCurrentTCB  \n"
    ::"i"(configMAX_SYSCALL_INTERRUPT_PRIORITY)
    );

【讨论】：

非常感谢朋友！！真正的救星。