Diff: platform/critical.h

Revision:

0:f269e3021894

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+++ b/platform/critical.h	Sun Oct 23 15:10:02 2016 +0000
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+
+/** \addtogroup platform */
+/** @{*/
+/*
+ * Copyright (c) 2015-2016, ARM Limited, All Rights Reserved
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may
+ * not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef __MBED_UTIL_CRITICAL_H__
+#define __MBED_UTIL_CRITICAL_H__
+
+#include <stdbool.h>
+#include <stdint.h>
+#include <stddef.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+
+/** Determine the current interrupts enabled state
+  *
+  * This function can be called to determine whether or not interrupts are currently enabled.
+  * \note
+  * NOTE:
+  * This function works for both cortex-A and cortex-M, although the underlyng implementation
+  * differs.
+  * @return true if interrupts are enabled, false otherwise
+  */
+bool core_util_are_interrupts_enabled(void);
+
+/** Mark the start of a critical section
+  *
+  * This function should be called to mark the start of a critical section of code.
+  * \note
+  * NOTES:
+  * 1) The use of this style of critical section is targetted at C based implementations.
+  * 2) These critical sections can be nested.
+  * 3) The interrupt enable state on entry to the first critical section (of a nested set, or single
+  *    section) will be preserved on exit from the section.
+  * 4) This implementation will currently only work on code running in privileged mode.
+  */
+void core_util_critical_section_enter(void);
+
+/** Mark the end of a critical section
+  *
+  * This function should be called to mark the end of a critical section of code.
+  * \note
+  * NOTES:
+  * 1) The use of this style of critical section is targetted at C based implementations.
+  * 2) These critical sections can be nested.
+  * 3) The interrupt enable state on entry to the first critical section (of a nested set, or single
+  *    section) will be preserved on exit from the section.
+  * 4) This implementation will currently only work on code running in privileged mode.
+  */
+void core_util_critical_section_exit(void);
+
+/**
+ * Atomic compare and set. It compares the contents of a memory location to a
+ * given value and, only if they are the same, modifies the contents of that
+ * memory location to a given new value. This is done as a single atomic
+ * operation. The atomicity guarantees that the new value is calculated based on
+ * up-to-date information; if the value had been updated by another thread in
+ * the meantime, the write would fail due to a mismatched expectedCurrentValue.
+ *
+ * Refer to https://en.wikipedia.org/wiki/Compare-and-set [which may redirect
+ * you to the article on compare-and swap].
+ *
+ * @param  ptr                  The target memory location.
+ * @param[in,out] expectedCurrentValue A pointer to some location holding the
+ *                              expected current value of the data being set atomically.
+ *                              The computed 'desiredValue' should be a function of this current value.
+ *                              @Note: This is an in-out parameter. In the
+ *                              failure case of atomic_cas (where the
+ *                              destination isn't set), the pointee of expectedCurrentValue is
+ *                              updated with the current value.
+ * @param[in] desiredValue      The new value computed based on '*expectedCurrentValue'.
+ *
+ * @return                      true if the memory location was atomically
+ *                              updated with the desired value (after verifying
+ *                              that it contained the expectedCurrentValue),
+ *                              false otherwise. In the failure case,
+ *                              exepctedCurrentValue is updated with the new
+ *                              value of the target memory location.
+ *
+ * pseudocode:
+ * function cas(p : pointer to int, old : pointer to int, new : int) returns bool {
+ *     if *p != *old {
+ *         *old = *p
+ *         return false
+ *     }
+ *     *p = new
+ *     return true
+ * }
+ *
+ * @Note: In the failure case (where the destination isn't set), the value
+ * pointed to by expectedCurrentValue is still updated with the current value.
+ * This property helps writing concise code for the following incr:
+ *
+ * function incr(p : pointer to int, a : int) returns int {
+ *     done = false
+ *     value = *p // This fetch operation need not be atomic.
+ *     while not done {
+ *         done = atomic_cas(p, &value, value + a) // *value gets updated automatically until success
+ *     }
+ *     return value + a
+ * }
+ */
+bool core_util_atomic_cas_u8(uint8_t *ptr, uint8_t *expectedCurrentValue, uint8_t desiredValue);
+
+/**
+ * Atomic compare and set. It compares the contents of a memory location to a
+ * given value and, only if they are the same, modifies the contents of that
+ * memory location to a given new value. This is done as a single atomic
+ * operation. The atomicity guarantees that the new value is calculated based on
+ * up-to-date information; if the value had been updated by another thread in
+ * the meantime, the write would fail due to a mismatched expectedCurrentValue.
+ *
+ * Refer to https://en.wikipedia.org/wiki/Compare-and-set [which may redirect
+ * you to the article on compare-and swap].
+ *
+ * @param  ptr                  The target memory location.
+ * @param[in,out] expectedCurrentValue A pointer to some location holding the
+ *                              expected current value of the data being set atomically.
+ *                              The computed 'desiredValue' should be a function of this current value.
+ *                              @Note: This is an in-out parameter. In the
+ *                              failure case of atomic_cas (where the
+ *                              destination isn't set), the pointee of expectedCurrentValue is
+ *                              updated with the current value.
+ * @param[in] desiredValue      The new value computed based on '*expectedCurrentValue'.
+ *
+ * @return                      true if the memory location was atomically
+ *                              updated with the desired value (after verifying
+ *                              that it contained the expectedCurrentValue),
+ *                              false otherwise. In the failure case,
+ *                              exepctedCurrentValue is updated with the new
+ *                              value of the target memory location.
+ *
+ * pseudocode:
+ * function cas(p : pointer to int, old : pointer to int, new : int) returns bool {
+ *     if *p != *old {
+ *         *old = *p
+ *         return false
+ *     }
+ *     *p = new
+ *     return true
+ * }
+ *
+ * @Note: In the failure case (where the destination isn't set), the value
+ * pointed to by expectedCurrentValue is still updated with the current value.
+ * This property helps writing concise code for the following incr:
+ *
+ * function incr(p : pointer to int, a : int) returns int {
+ *     done = false
+ *     value = *p // This fetch operation need not be atomic.
+ *     while not done {
+ *         done = atomic_cas(p, &value, value + a) // *value gets updated automatically until success
+ *     }
+ *     return value + a
+ * }
+ */
+bool core_util_atomic_cas_u16(uint16_t *ptr, uint16_t *expectedCurrentValue, uint16_t desiredValue);
+
+/**
+ * Atomic compare and set. It compares the contents of a memory location to a
+ * given value and, only if they are the same, modifies the contents of that
+ * memory location to a given new value. This is done as a single atomic
+ * operation. The atomicity guarantees that the new value is calculated based on
+ * up-to-date information; if the value had been updated by another thread in
+ * the meantime, the write would fail due to a mismatched expectedCurrentValue.
+ *
+ * Refer to https://en.wikipedia.org/wiki/Compare-and-set [which may redirect
+ * you to the article on compare-and swap].
+ *
+ * @param  ptr                  The target memory location.
+ * @param[in,out] expectedCurrentValue A pointer to some location holding the
+ *                              expected current value of the data being set atomically.
+ *                              The computed 'desiredValue' should be a function of this current value.
+ *                              @Note: This is an in-out parameter. In the
+ *                              failure case of atomic_cas (where the
+ *                              destination isn't set), the pointee of expectedCurrentValue is
+ *                              updated with the current value.
+ * @param[in] desiredValue      The new value computed based on '*expectedCurrentValue'.
+ *
+ * @return                      true if the memory location was atomically
+ *                              updated with the desired value (after verifying
+ *                              that it contained the expectedCurrentValue),
+ *                              false otherwise. In the failure case,
+ *                              exepctedCurrentValue is updated with the new
+ *                              value of the target memory location.
+ *
+ * pseudocode:
+ * function cas(p : pointer to int, old : pointer to int, new : int) returns bool {
+ *     if *p != *old {
+ *         *old = *p
+ *         return false
+ *     }
+ *     *p = new
+ *     return true
+ * }
+ *
+ * @Note: In the failure case (where the destination isn't set), the value
+ * pointed to by expectedCurrentValue is still updated with the current value.
+ * This property helps writing concise code for the following incr:
+ *
+ * function incr(p : pointer to int, a : int) returns int {
+ *     done = false
+ *     value = *p // This fetch operation need not be atomic.
+ *     while not done {
+ *         done = atomic_cas(p, &value, value + a) // *value gets updated automatically until success
+ *     }
+ *     return value + a
+ * }
+ */
+bool core_util_atomic_cas_u32(uint32_t *ptr, uint32_t *expectedCurrentValue, uint32_t desiredValue);
+
+/**
+ * Atomic compare and set. It compares the contents of a memory location to a
+ * given value and, only if they are the same, modifies the contents of that
+ * memory location to a given new value. This is done as a single atomic
+ * operation. The atomicity guarantees that the new value is calculated based on
+ * up-to-date information; if the value had been updated by another thread in
+ * the meantime, the write would fail due to a mismatched expectedCurrentValue.
+ *
+ * Refer to https://en.wikipedia.org/wiki/Compare-and-set [which may redirect
+ * you to the article on compare-and swap].
+ *
+ * @param  ptr                  The target memory location.
+ * @param[in,out] expectedCurrentValue A pointer to some location holding the
+ *                              expected current value of the data being set atomically.
+ *                              The computed 'desiredValue' should be a function of this current value.
+ *                              @Note: This is an in-out parameter. In the
+ *                              failure case of atomic_cas (where the
+ *                              destination isn't set), the pointee of expectedCurrentValue is
+ *                              updated with the current value.
+ * @param[in] desiredValue      The new value computed based on '*expectedCurrentValue'.
+ *
+ * @return                      true if the memory location was atomically
+ *                              updated with the desired value (after verifying
+ *                              that it contained the expectedCurrentValue),
+ *                              false otherwise. In the failure case,
+ *                              exepctedCurrentValue is updated with the new
+ *                              value of the target memory location.
+ *
+ * pseudocode:
+ * function cas(p : pointer to int, old : pointer to int, new : int) returns bool {
+ *     if *p != *old {
+ *         *old = *p
+ *         return false
+ *     }
+ *     *p = new
+ *     return true
+ * }
+ *
+ * @Note: In the failure case (where the destination isn't set), the value
+ * pointed to by expectedCurrentValue is still updated with the current value.
+ * This property helps writing concise code for the following incr:
+ *
+ * function incr(p : pointer to int, a : int) returns int {
+ *     done = false
+ *     value = *p // This fetch operation need not be atomic.
+ *     while not done {
+ *         done = atomic_cas(p, &value, value + a) // *value gets updated automatically until success
+ *     }
+ *     return value + a
+ * }
+ */
+bool core_util_atomic_cas_ptr(void **ptr, void **expectedCurrentValue, void *desiredValue);
+
+/**
+ * Atomic increment.
+ * @param  valuePtr Target memory location being incremented.
+ * @param  delta    The amount being incremented.
+ * @return          The new incremented value.
+ */
+uint8_t core_util_atomic_incr_u8(uint8_t *valuePtr, uint8_t delta);
+
+/**
+ * Atomic increment.
+ * @param  valuePtr Target memory location being incremented.
+ * @param  delta    The amount being incremented.
+ * @return          The new incremented value.
+ */
+uint16_t core_util_atomic_incr_u16(uint16_t *valuePtr, uint16_t delta);
+
+/**
+ * Atomic increment.
+ * @param  valuePtr Target memory location being incremented.
+ * @param  delta    The amount being incremented.
+ * @return          The new incremented value.
+ */
+uint32_t core_util_atomic_incr_u32(uint32_t *valuePtr, uint32_t delta);
+
+/**
+ * Atomic increment.
+ * @param  valuePtr Target memory location being incremented.
+ * @param  delta    The amount being incremented in bytes.
+ * @return          The new incremented value.
+ *
+ * @note The type of the pointer argument is not taken into account
+ *       and the pointer is incremented by bytes.
+ */
+void *core_util_atomic_incr_ptr(void **valuePtr, ptrdiff_t delta);
+
+/**
+ * Atomic decrement.
+ * @param  valuePtr Target memory location being decremented.
+ * @param  delta    The amount being decremented.
+ * @return          The new decremented value.
+ */
+uint8_t core_util_atomic_decr_u8(uint8_t *valuePtr, uint8_t delta);
+
+/**
+ * Atomic decrement.
+ * @param  valuePtr Target memory location being decremented.
+ * @param  delta    The amount being decremented.
+ * @return          The new decremented value.
+ */
+uint16_t core_util_atomic_decr_u16(uint16_t *valuePtr, uint16_t delta);
+
+/**
+ * Atomic decrement.
+ * @param  valuePtr Target memory location being decremented.
+ * @param  delta    The amount being decremented.
+ * @return          The new decremented value.
+ */
+uint32_t core_util_atomic_decr_u32(uint32_t *valuePtr, uint32_t delta);
+
+/**
+ * Atomic decrement.
+ * @param  valuePtr Target memory location being decremented.
+ * @param  delta    The amount being decremented in bytes.
+ * @return          The new decremented value.
+ *
+ * @note The type of the pointer argument is not taken into account
+ *       and the pointer is decremented by bytes
+ */
+void *core_util_atomic_decr_ptr(void **valuePtr, ptrdiff_t delta);
+
+#ifdef __cplusplus
+} // extern "C"
+#endif
+
+
+#endif // __MBED_UTIL_CRITICAL_H__
+
+/** @}*/