打印重定向

为了观察睡眠时间，重定向打印函数，打印的时候将时间戳打印出来，实现如下

#define printf(fmt, ...)                                                    \do                                                                      \{                                                                       \char time_buf[20];                                                  \time_t now = time(NULL);                                            \struct tm *tm_info = localtime(&now);                               \strftime(time_buf, sizeof(time_buf), "%Y-%m-%d %H:%M:%S", tm_info); \fprintf(stdout, "[%s] " fmt, time_buf, ##__VA_ARGS__);              \} while (0)

FreeRTOSConfig.h 配置

#define configTICK_RATE_HZ                         ( 1000 )                  /* In this non-real time simulated environment the tick frequency has to be at least a multiple of the Win32 tick frequency, and therefore very slow. */#define configUSE_TICKLESS_IDLE                   1
#define configEXPECTED_IDLE_TIME_BEFORE_SLEEP     10

portmacro.h 实现

#ifndef portSUPPRESS_TICKS_AND_SLEEPextern void vPortSuppressTicksAndSleep( TickType_t xExpectedIdleTime );#define portSUPPRESS_TICKS_AND_SLEEP( xExpectedIdleTime )    vPortSuppressTicksAndSleep( xExpectedIdleTime )
#endif

低功耗流程

task.c 文件中

if (xExpectedIdleTime >= (TickType_t)configEXPECTED_IDLE_TIME_BEFORE_SLEEP)
{vTaskSuspendAll();{/* Now the scheduler is suspended, the expected idle* time can be sampled again, and this time its value can* be used. */configASSERT(xNextTaskUnblockTime >= xTickCount);xExpectedIdleTime = prvGetExpectedIdleTime();/* Define the following macro to set xExpectedIdleTime to 0* if the application does not want* portSUPPRESS_TICKS_AND_SLEEP() to be called. */configPRE_SUPPRESS_TICKS_AND_SLEEP_PROCESSING(xExpectedIdleTime);if (xExpectedIdleTime >= (TickType_t)configEXPECTED_IDLE_TIME_BEFORE_SLEEP){traceLOW_POWER_IDLE_BEGIN();portSUPPRESS_TICKS_AND_SLEEP(xExpectedIdleTime);traceLOW_POWER_IDLE_END();}else{mtCOVERAGE_TEST_MARKER();}}(void)xTaskResumeAll();
}
else
{mtCOVERAGE_TEST_MARKER();
}

低功耗函数主要在 vPortSuppressTicksAndSleep函数，睡眠时间阈值通过宏 configEXPECTED_IDLE_TIME_BEFORE_SLEEP，如果睡眠时间小于改值，就不进入睡眠。

vPortSuppressTicksAndSleep 实现

void vPortSuppressTicksAndSleep(TickType_t xExpectedIdleTime)
{struct timespec xSleepTime;TickType_t xModifiableIdleTime;uint64_t xStartTime, xEndTime, xElapsedTime;/* Stop the timer interrupt here (emulated by blocking SIGALRM). */pthread_sigmask(SIG_BLOCK, &xAllSignals, NULL);/* Record the start time. */xStartTime = prvGetTimeNs();/* Prepare the sleep time in nanoseconds. */xSleepTime.tv_sec = xExpectedIdleTime / configTICK_RATE_HZ;xSleepTime.tv_nsec = (xExpectedIdleTime % configTICK_RATE_HZ) * (1000000000 / configTICK_RATE_HZ);/* Enter low-power state. */nanosleep(&xSleepTime, NULL);/* Record the end time. */xEndTime = prvGetTimeNs();/* Calculate elapsed time. */xElapsedTime = (xEndTime - xStartTime) / (1000000000 / configTICK_RATE_HZ);printf("sleep time: %d\r\n", xExpectedIdleTime);/* Adjust system ticks. */vTaskStepTick((TickType_t)xElapsedTime);/* Restart the timer interrupt. */pthread_sigmask(SIG_UNBLOCK, &xAllSignals, NULL);
}

测试

新建一个 task，1000ms 打印一次

static void printf_task( void * pvParameters )
{( void ) pvParameters;for( ; ; ){vTaskDelay(1000);console_print( "task1\n" );}
}

xTaskCreate( printf_task,            "Rx",                           configMINIMAL_STACK_SIZE,       NULL,                           tskIDLE_PRIORITY + 2,NULL );                         

效果

[2024-11-29 12:36:14] sleep time: 1000
[2024-11-29 12:36:14] task1
[2024-11-29 12:36:15] sleep time: 1000
[2024-11-29 12:36:15] task1
[2024-11-29 12:36:16] sleep time: 1000
[2024-11-29 12:36:16] task1
[2024-11-29 12:36:17] sleep time: 1000
[2024-11-29 12:36:17] task1
[2024-11-29 12:36:18] sleep time: 1000
[2024-11-29 12:36:18] task1
[2024-11-29 12:36:19] sleep time: 1000
[2024-11-29 12:36:19] task1
[2024-11-29 12:36:20] sleep time: 1000
[2024-11-29 12:36:20] task1

从结果中可以看到，每次睡眠 1000ms，任务还是 1000ms 打印一次。

注意事项

移植 vPortSuppressTicksAndSleep 到 MCU 上时，最重要的是利用 MCU 的硬件支持来管理低功耗模式，合理配置系统的时钟源和中断源，以确保系统能在需要时唤醒并继续精确计时。需要考虑的核心问题包括：

• 低功耗模式选择和外设管理。
• 定时器和中断的正确配置。
• 实际休眠时间的计算和系统时钟同步。
• 调试和验证。

通过以上方法，能确保移植后的系统能在保证精度的同时有效降低功耗。