cpu_relax(): New function.

[bertos.git] / bertos / cpu / power.h

diff --git a/bertos/cpu/power.h b/bertos/cpu/power.h
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+/**
+ * \file
+ * <!--
+ * This file is part of BeRTOS.
+ *
+ * Bertos is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+ *
+ * As a special exception, you may use this file as part of a free software
+ * library without restriction.  Specifically, if other files instantiate
+ * templates or use macros or inline functions from this file, or you compile
+ * this file and link it with other files to produce an executable, this
+ * file does not by itself cause the resulting executable to be covered by
+ * the GNU General Public License.  This exception does not however
+ * invalidate any other reasons why the executable file might be covered by
+ * the GNU General Public License.
+ *
+ * Copyright 2008 Bernie Innocenti <bernie@codewiz.org>
+ * -->
+ *
+ * \brief CPU power management functions
+ *
+ * \author Bernie Innocenti <bernie@codewiz.org>
+ */
+
+#ifndef CPU_POWER_H
+#define CPU_POWER_H
+
+#include <cfg/cfg_kern.h>
+#include <cfg/cfg_wdt.h>
+
+#if CONFIG_KERNEL
+       #include <kern/proc.h>
+#endif
+
+#if CONFIG_WATCHDOG
+       #include <drv/wdt.h>
+#endif
+
+/**
+ * Let the CPU rest in tight busy loops
+ *
+ * User code that sits in a busy loop should call cpu_relax() every
+ * once in a while to perform system-depndent idle processing.
+ *
+ * Depending on the system configuration, this might perform different
+ * actions:
+ *
+ *  - yield the CPU to other processes
+ *  - reset the watchdog timer to avoid it from triggering
+ *  - scale the CPU speed down to save power (unimplemented)
+ *  - let the event loop of the emulator process a few events
+ */
+INLINE void cpu_relax(void)
+{
+#if CONFIG_KERNEL
+       proc_yield();
+#endif
+
+#if CONFIG_WATCHDOG
+       wdt_reset();
+#endif
+}
+
+/**
+ * Stop the processor until the next interrupt occurs.
+ *
+ * Pausing the CPU effectively reduces power usage, and should be used
+ * whenever the program is idle waiting for the next event to occur.
+ *
+ * To avoid deadlocking, the caller should normally check for the
+ * desired condition with interrupts disabled, and enter this function
+ * while interrupts are still disabled:
+ *
+ * \code
+ *     IRQ_DISABLE();
+ *     while (!event_occurred)
+ *         cpu_pause();
+ *     IRQ_ENABLE();
+ * \endcode
+ *
+ * \note Some implementations of cpu_pause() may return before any interrupt has occurred
+ *       Caller code should be written taking this into account.
+ *
+ * \note This function is currently unimplemented
+ */
+INLINE void cpu_pause(void)
+{
+       //ASSERT_IRQ_DISABLED();
+       //IRQ_ENABLE();
+       cpu_relax();
+       //IRQ_DISABLE();
+}
+
+/**
+ * Safely call cpu_pause() until the COND predicate becomes true.
+ */
+#define CPU_PAUSE_ON(COND) ATOMIC(while (!(COND)) { cpu_pause(); })
+
+#endif /* CPU_POWER_H */