Add tickless idle support (suppress peridic timer interrupt when slee…

…ping).
picoos · Apr 18, 2016 · 325f015 · 325f015
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diff --git a/README.md b/README.md
@@ -19,9 +19,10 @@ There is some information about these in [my blogs][2].
 
 Other changes are:
 
+- Power management API to provide framework for MCU power saving / sleeping features
+- Suppression of timer interrupts during idle mode (tickless idle). Complete implementation is available in cortex-m/stm32 port.
 - stdarg support for nano layer printf-functions
 - Makefile system uses GNU make pattern rules for source directory handling (otherwise projects that had many directories run into troubles)
-- Power management API to provide framework for MCU power saving / sleeping features
 
 
 Updated doxygen manual is available [here][3].

diff --git a/examples/poscfg.h b/examples/poscfg.h
@@ -522,16 +522,26 @@
 /** Enable power management api.
  * If this definition is set to 1, pico]OS power management functions
  * are included into kernel. Note that architecture port must support
- * power management.
+ * power management. Architecture port is expected to provide
+ * implementation for ::p_pos_powerSleep.
  */
 #define POSCFG_FEATURE_POWER         0
 
 /** Enable interrupt wakeup support in power management.
  * If this definition is set to 1, pico]OS allows system to
  * stay in sleep until a interrupt causes context switch away
- * from idle task.
+ * from idle task. If not enabled, it is assumed that
+ * interrupt will wake up a sleeping system. Architecture port
+ * is expected to privide implementation for ::p_pos_powerWakeup.
  */
 #define POSCFG_FEATURE_POWER_WAKEUP  1
+
+/** Enable supression of periodic timer interrupt when
+ * when system is sleeping to save power. Architecture port
+ * is expected to provide implementations for ::p_pos_powerTickSuspend and
+ * ::p_pos_powerTickResume.
+ */
+#define POSCFG_FEATURE_TICKLESS  1
 /** @} */
 
 

diff --git a/inc/picoos.h b/inc/picoos.h
@@ -94,6 +94,7 @@
  *  - idle system placed into sleep to save power
  *  - optional support for filtering out wakeups that won't result
  *    in task activation
+ *  - tickless idle support
  *
  * <b>Miscellaneous:</b>
  *  - atomic variables
@@ -1512,8 +1513,32 @@ POSEXTERN void POSCALL c_pos_intExitQuick(void);      /* picoos.c */
  */
 POSEXTERN void POSCALL c_pos_timerInterrupt(void);      /* picoos.c */
 
-#if (DOX!=0) || POSCFG_FEATURE_POWER == 1
+#if (DOX!=0) || POSCFG_FEATURE_TICKLESS == 1
 
+/**
+ * Timer interrupt control function.
+ * This function can be called instead of ::c_pos_timerInterrupt when
+ * using dynamic tick rate (0 <= tick rate < HZ)to save power. Inside ::p_pos_powerSleep,
+ * ::c_pos_nextWakeup() can be used to obtain expected amount of idle time.
+ * Tick rate can then be slowed down or completely suspended until
+ * idle time has expired. Processor is then put into sleep. After wakeup, 
+ * number of ticks spent in sleep should be calculated and
+ * passed to pico]OS kernel with this function.
+ *
+ * @sa      p_pos_powerSleep, c_pos_nextWakeup
+ */
+POSEXTERN void POSCALL c_pos_timerStep(UVAR_t ticks);      /* picoos.c */
+
+/**
+ * Task function.
+ * Return number of ticks until next task should wake up.
+ * @return  Number of ticks system can safely sleep or INFINITE.
+ */
+POSEXTERN UINT_t POSCALL c_pos_nextWakeup(void);
+
+#endif
+
+#if (DOX!=0) || POSCFG_FEATURE_POWER == 1
 /**
  * Called by idle task when system should fall in sleep.
  * @note    This function is not part of the pico]OS. It must be
@@ -1537,6 +1562,30 @@ POSFROMEXT void POSCALL p_pos_powerWakeup(void);    /* arch_c.c */
 #endif
 #endif
 
+#if (DOX!=0) || POSCFG_FEATURE_TICKLESS == 1
+/**
+ * Called by p_pos_powerSleep to begin tickless idle period. Function
+ * should disable periodic timer interrupt and initialize a timer
+ * that wakes system up from sleep after given time has passed.
+ * @note    This function is not part of the pico]OS. It must be
+ *          provided by the user, since it is architecture specific.
+ * @sa      p_pos_powerSleep, p_pos_powerTickResume
+ */
+POSFROMEXT void POSCALL p_pos_powerTickSuspend(UVAR_t ticks);
+
+/**
+ * Called by p_pos_powerSleep to end tickless idle period. Function
+ * should cancel possible wakeup timer and update system tick count
+ * by calling c_pos_timerStep with amount of time slept. After that
+ * periodic timer tick must be re-enabled.
+ * @note    This function is not part of the pico]OS. It must be
+ *          provided by the user, since it is architecture specific.
+ * @sa      p_pos_powerSleep, p_pos_powerTickSuspend
+ */
+POSFROMEXT void POSCALL p_pos_powerTickResume(void);
+
+#endif
+
 /** @} */
 
 

diff --git a/ports/cortex-m/arch_c.c b/ports/cortex-m/arch_c.c
@@ -562,6 +562,31 @@ void p_pos_powerSleep()
     return;
 
 #endif
+#endif
+
+  uint32_t oldStatus;
+
+  // Ensure flag that __WFE waits for is not set yet
+  __SEV();
+  __WFE();
+
+#if POSCFG_FEATURE_TICKLESS
+
+  UVAR_t nextWake = c_pos_nextWakeup();
+  bool restoreTick = false;
+  bool restoreDeepSleep = false;
+
+  if (nextWake < MS(100)) {
+
+    restoreDeepSleep = SCB->SCR & SCB_SCR_SLEEPDEEP_Msk;
+    SCB->SCR &= ~SCB_SCR_SLEEPDEEP_Msk;
+  }
+  else {
+
+    p_pos_powerTickSuspend(nextWake);
+    restoreTick = true;
+  }
+
 #endif
 
 #if POSCFG_FEATURE_POWER_WAKEUP != 0
@@ -574,28 +599,40 @@ void p_pos_powerSleep()
   SCB->SCR |= SCB_SCR_SLEEPONEXIT_Msk; // Sleep after interrupt
 #endif
 
-  uint32_t oldStatus;
-
-  // Ensure flag that __WFE waits for is not set yet
-  __SEV();
-  __WFE();
-
 #if __CORTEX_M < 3
 
-  oldStatus = __get_PRIMASK();
-  __disable_irq();
-  __WFE();
-  if (oldStatus)
-    __enable_irq();
+  __enable_irq();
 
 #else
 
   oldStatus = __get_BASEPRI();
   __set_BASEPRI(0);
+
+#endif
+
+  __DSB();
   __WFE();
+
+#if __CORTEX_M < 3
+
+  __disableirq();
+
+#else
+
   __set_BASEPRI(oldStatus);
 
 #endif
+
+#if POSCFG_FEATURE_TICKLESS
+
+  if (restoreDeepSleep)
+    SCB->SCR |= SCB_SCR_SLEEPDEEP_Msk;
+
+  if (restoreTick)
+    p_pos_powerTickResume();
+
+#endif
+
 }
 
 #endif

diff --git a/ports/cortex-m/port.h b/ports/cortex-m/port.h
@@ -597,6 +597,7 @@ extern unsigned char *portIrqStack;
 void portInitClock(void);
 void portInitConsole(void);
 void portSystemInit(void);
+void portRestoreClocksAfterWakeup(void);
 
 typedef void (* const PortExcHandlerFunc)(void);
 

diff --git a/ports/cortex-m/stm32/con_usart.c b/ports/cortex-m/stm32/con_usart.c
@@ -60,6 +60,11 @@ void portInitConsole(void)
   USART_Init(USARTx, &init);
   USART_Cmd(USARTx, ENABLE);
 
+#if POSCFG_FEATURE_POWER
+
+  // Enable transmission complete interrupt
+#endif
+
 #if NOSCFG_FEATURE_CONIN == 1
 
   // Enable receive data interrupt.
@@ -73,6 +78,10 @@ void portInitConsole(void)
   NVIC_EnableIRQ(USARTx_IRQn);
 }
 
+#if POSCFG_FEATURE_POWER
+static bool busy = false;
+#endif
+
 /*
  * Uart interrupt handler.
  */
@@ -82,10 +91,22 @@ void USARTx_IRQHandler()
   c_pos_intEnter();
 
 #if NOSCFG_FEATURE_CONOUT == 1
+
+#if POSCFG_FEATURE_POWER
+  if (USART_GetITStatus(USARTx, USART_IT_TC) == SET) {
+
+    USART_ITConfig(USARTx, USART_IT_TC, DISABLE);
+    if (busy) {
+
+      posPowerEnableSleep();
+      busy = false;
+    }
+  }
+#endif
+
   if (USART_GetITStatus(USARTx, USART_IT_TXE) == SET) {
 
     USART_ITConfig (USARTx, USART_IT_TXE, DISABLE);
-    posPowerEnableSleep();
     c_nos_putcharReady();
   }
 #endif
@@ -116,9 +137,20 @@ p_putchar(char c)
   if (USART_GetFlagStatus(USARTx, USART_FLAG_TXE) == RESET)
     return 0;
 
-  posPowerDisableSleep();
   USART_SendData(USARTx, c);
   USART_ITConfig (USARTx, USART_IT_TXE, ENABLE);
+
+#if POSCFG_FEATURE_POWER
+
+  if (!busy) {
+
+    USART_ITConfig(USARTx, USART_IT_TC, ENABLE);
+    posPowerDisableSleep();
+    busy = true;
+  }
+
+#endif
+
   return 1;
 }
 #endif