踩准时钟节拍、玩转时间转换，鸿蒙轻内核时间管理有妙招

1、时间管理初始化和启动

#define OS_SYS_CLOCK                                        96000000
#define LOSCFG_BASE_CORE_TICK_PER_SECOND                    (1000UL)
#define LOSCFG_BASE_CORE_TICK_HW_TIME                       0

1.2 时间管理初始化和启动

LITE_OS_SEC_TEXT_INIT UINT32 LOS_Start(VOID)
{
    return HalStartSchedule(OsTickHandler);
}

函数UINT32 HalTickStart(OS_TICK_HANDLER *handler)定义在kernel\arch\arm\cortex-m7\gcc\los_context.c，源码如下。其中函数参数为Tick中断处理函数OsTickHandler()，后文会分析该tick中断处理函数。⑴处代码继续调用函数进一步调用函数HalTickStart(handler)来设置Tick中断启动。⑵处会调用汇编函数HalStartToRun开始运行系统，后续任务调度系列再详细分析该汇编函数。

LITE_OS_SEC_TEXT_INIT UINT32 HalStartSchedule(OS_TICK_HANDLER handler)
{
    UINT32 ret;
⑴  ret = HalTickStart(handler);
    if (ret != LOS_OK) {
        return ret;
    }
⑵  HalStartToRun();
    return LOS_OK; /* never return */
}

函数HalTickStart(handler)定义在文件kernel\arch\arm\cortex-m7\gcc\los_timer.c，源码如下，我们分析下函数的代码实现。⑴处校验下时间管理模块的配置项的合法性。在开启宏LOSCFG_USE_SYSTEM_DEFINED_INTERRUPT时，会使用系统定义的中断。会执行⑵处的代码，调用定义在文件kernel\arch\arm\cortex-m7\gcc\los_interrupt.c中的函数OsSetVector()设置中断向量，该函数在中断系列会详细分析。⑶处设置全局变量g_sysClock为系统时钟，g_cyclesPerTick为每tick对应的cycle数目，g_ullTickCount初始化为0，表示系统tick中断发生次数。⑷处调用定义在targets\cortex-m7_nucleo_f767zi_gcc\Drivers\CMSIS\Include\core_cm7.h文件中的内联函数uint32_t SysTick_Config(uint32_t ticks)，初始化、启动系统定时器Systick和中断。

WEAK UINT32 HalTickStart(OS_TICK_HANDLER *handler)
{
    UINT32 ret;

⑴  if ((OS_SYS_CLOCK == 0) ||
        (LOSCFG_BASE_CORE_TICK_PER_SECOND == 0) ||
        (LOSCFG_BASE_CORE_TICK_PER_SECOND > OS_SYS_CLOCK)) {
        return LOS_ERRNO_TICK_CFG_INVALID;
    }

#if (LOSCFG_USE_SYSTEM_DEFINED_INTERRUPT == 1)
#if (OS_HWI_WITH_ARG == 1)
    OsSetVector(SysTick_IRQn, (HWI_PROC_FUNC)handler, NULL);
#else
⑵  OsSetVector(SysTick_IRQn, (HWI_PROC_FUNC)handler);
#endif
#endif

⑶  g_sysClock = OS_SYS_CLOCK;
    g_cyclesPerTick = OS_SYS_CLOCK / LOSCFG_BASE_CORE_TICK_PER_SECOND;
    g_ullTickCount = 0;

⑷  ret = SysTick_Config(g_cyclesPerTick);
    if (ret == 1) {
        return LOS_ERRNO_TICK_PER_SEC_TOO_SMALL;
    }

    return LOS_OK;
}

1.3 Tick中断处理函数OsTickHandler()

LITE_OS_SEC_TEXT VOID OsTickHandler(VOID)
{
#if (LOSCFG_BASE_CORE_TICK_HW_TIME == 1)
⑴  platform_tick_handler();
#endif

⑵  g_ullTickCount++;

#if (LOSCFG_BASE_CORE_TIMESLICE == 1)
⑶  OsTimesliceCheck();
#endif

⑷   OsTaskScan();  // task timeout scan

#if (LOSCFG_BASE_CORE_SWTMR == 1)
⑸  (VOID)OsSwtmrScan();
#endif
}

2、LiteOS内核时间管理常用操作

LITE_OS_SEC_TEXT_MINOR UINT32 LOS_MS2Tick(UINT32 millisec)
{
    if (millisec == OS_NULL_INT) {
        return OS_NULL_INT;
    }

    return ((UINT64)millisec * LOSCFG_BASE_CORE_TICK_PER_SECOND) / OS_SYS_MS_PER_SECOND;
}

2.1.2 Tick转化为毫秒

LITE_OS_SEC_TEXT_MINOR UINT32 LOS_Tick2MS(UINT32 ticks)
{
    return ((UINT64)ticks * OS_SYS_MS_PER_SECOND) / LOSCFG_BASE_CORE_TICK_PER_SECOND;
}

2.1.3 Cycle数目转化为毫秒

typedef struct tagCpuTick {
    UINT32 cntHi; /* < 一个64位数值的高32位 */
    UINT32 cntLo; /* < 一个64位数值的低32位 */
} CpuTick;

继续看转换函数OsCpuTick2MS()，它可以把CpuTick类型表示的cycle数目转换为对应的毫秒数，输出毫秒数据的高、低32位数值。看下具体的代码，⑴处校验参数是否为空指针，⑵处检查系统时钟是否配置。⑶处把CpuTick结构体表示的cycle数目转化为UINT64类型数据。⑷处进行数值计算，(DOUBLE)g_sysClock / OS_SYS_MS_PER_SECOND得到每毫秒多少个cycle数，然后和tmpCpuTick做除法运算，得到cycle数目对应的毫秒数目。⑸处把DOUBLE类型转换为UINT64类型，然后执行⑹，分别把结果数值的高、低64位赋值给*msLo、*msHi。

LITE_OS_SEC_TEXT_INIT UINT32 OsCpuTick2MS(CpuTick *cpuTick, UINT32 *msHi, UINT32 *msLo)
{
    UINT64 tmpCpuTick;
    DOUBLE temp;

⑴  if ((cpuTick == NULL) || (msHi == NULL) || (msLo == NULL)) {
        return LOS_ERRNO_SYS_PTR_NULL;
    }

⑵  if (g_sysClock == 0) {
        return LOS_ERRNO_SYS_CLOCK_INVALID;
    }
⑶  tmpCpuTick = ((UINT64)cpuTick->cntHi << OS_SYS_MV_32_BIT) | cpuTick->cntLo;
⑷  temp = tmpCpuTick / ((DOUBLE)g_sysClock / OS_SYS_MS_PER_SECOND);

    tmpCpuTick = (UINT64)temp;

    *msLo = (UINT32)tmpCpuTick;
    *msHi = (UINT32)(tmpCpuTick >> OS_SYS_MV_32_BIT);

    return LOS_OK;
}

2.1.4 Cycle数目转化为微秒

LITE_OS_SEC_TEXT_INIT UINT32 OsCpuTick2US(CpuTick *cpuTick, UINT32 *usHi, UINT32 *usLo)
{
    UINT64 tmpCpuTick;
    DOUBLE temp;

    if ((cpuTick == NULL) || (usHi == NULL) || (usLo == NULL)) {
        return LOS_ERRNO_SYS_PTR_NULL;
    }

    if (g_sysClock == 0) {
        return LOS_ERRNO_SYS_CLOCK_INVALID;
    }
    tmpCpuTick = ((UINT64)cpuTick->cntHi << OS_SYS_MV_32_BIT) | cpuTick->cntLo;
    temp = tmpCpuTick / ((DOUBLE)g_sysClock / OS_SYS_US_PER_SECOND);

    tmpCpuTick = (UINT64)temp;

    *usLo = (UINT32)tmpCpuTick;
    *usHi = (UINT32)(tmpCpuTick >> OS_SYS_MV_32_BIT);

    return LOS_OK;
}

2.2 时间统计操作

LITE_OS_SEC_TEXT_MINOR UINT32 LOS_CyclePerTickGet(VOID)
{
    return g_cyclesPerTick;
}

2.2.2 获取自系统启动以来的Tick数

LITE_OS_SEC_TEXT_MINOR UINT64 LOS_TickCountGet(VOID)
{
    return g_ullTickCount;
}

2.2.3 获取系统时钟

UINT32 LOS_SysClockGet(VOID)
{
    return g_sysClock;
}

2.2.4 获取系统启动以来的Cycle数

LITE_OS_SEC_TEXT_MINOR VOID HalGetCpuCycle(UINT32 *cntHi, UINT32 *cntLo)
{
    UINT64 swTick;
    UINT64 cycle;
    UINT32 hwCycle;
    UINTPTR intSave;

    intSave = LOS_IntLock();

⑴  swTick = g_ullTickCount;
⑵  hwCycle = SysTick->VAL;

⑶  if ((SCB->ICSR & TICK_CHECK) != 0) {
        hwCycle = SysTick->VAL;
        swTick++;
    }

⑷  cycle = (((swTick) * g_cyclesPerTick) + (g_cyclesPerTick - hwCycle));

⑸  *cntHi = cycle >> SHIFT_32_BIT;
    *cntLo = cycle & CYCLE_CHECK;

    LOS_IntRestore(intSave);

    return;
}

小结