Merge pull request #1843 from c1728p9/atomic_access

Add functions for atomic access

hal/api/critical.h

@@ -18,6 +18,8 @@
 #ifndef __MBED_UTIL_CRITICAL_H__
 #define __MBED_UTIL_CRITICAL_H__
 
+#include <stdbool.h>
+
 #ifdef __cplusplus
 extern "C" {
 #endif
@@ -48,6 +50,213 @@ void core_util_critical_section_enter();
   */
 void core_util_critical_section_exit();
 
+/**
+ * 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 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 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);
+
 #ifdef __cplusplus
 } // extern "C"
 #endif

hal/common/critical.c

@@ -24,6 +24,8 @@
 // Module include
 #include "critical.h"
 
+#define EXCLUSIVE_ACCESS (!defined (__CORTEX_M0) && !defined (__CORTEX_M0PLUS))
+
 static volatile uint32_t interrupt_enable_counter = 0;
 static volatile uint32_t critical_primask = 0;
 
@@ -66,3 +68,215 @@ void core_util_critical_section_exit()
         }
     }
 }
+
+#if EXCLUSIVE_ACCESS
+
+bool core_util_atomic_cas_u8(uint8_t *ptr, uint8_t *expectedCurrentValue, uint8_t desiredValue)
+{
+    uint8_t currentValue = __LDREXB((volatile uint8_t*)ptr);
+    if (currentValue != *expectedCurrentValue) {
+        *expectedCurrentValue = currentValue;
+        __CLREX();
+        return false;
+    }
+
+    return !__STREXB(desiredValue, (volatile uint8_t*)ptr);
+}
+
+bool core_util_atomic_cas_u16(uint16_t *ptr, uint16_t *expectedCurrentValue, uint16_t desiredValue)
+{
+    uint16_t currentValue = __LDREXH((volatile uint16_t*)ptr);
+    if (currentValue != *expectedCurrentValue) {
+        *expectedCurrentValue = currentValue;
+        __CLREX();
+        return false;
+    }
+
+    return !__STREXH(desiredValue, (volatile uint16_t*)ptr);
+}
+
+
+bool core_util_atomic_cas_u32(uint32_t *ptr, uint32_t *expectedCurrentValue, uint32_t desiredValue)
+{
+    uint32_t currentValue = __LDREXW((volatile uint32_t*)ptr);
+    if (currentValue != *expectedCurrentValue) {
+        *expectedCurrentValue = currentValue;
+        __CLREX();
+        return false;
+    }
+
+    return !__STREXW(desiredValue, (volatile uint32_t*)ptr);
+}
+
+uint8_t core_util_atomic_incr_u8(uint8_t * valuePtr, uint8_t delta)
+{
+    uint8_t newValue;
+    do {
+        newValue = __LDREXB((volatile uint8_t*)valuePtr) + delta;
+    } while (__STREXB(newValue, (volatile uint8_t*)valuePtr));
+    return newValue;
+}
+
+uint16_t core_util_atomic_incr_u16(uint16_t * valuePtr, uint16_t delta)
+{
+    uint16_t newValue;
+    do {
+        newValue = __LDREXH((volatile uint16_t*)valuePtr) + delta;
+    } while (__STREXH(newValue, (volatile uint16_t*)valuePtr));
+    return newValue;
+}
+
+uint32_t core_util_atomic_incr_u32(uint32_t * valuePtr, uint32_t delta)
+{
+    uint32_t newValue;
+    do {
+        newValue = __LDREXW((volatile uint32_t*)valuePtr) + delta;
+    } while (__STREXW(newValue, (volatile uint32_t*)valuePtr));
+    return newValue;
+}
+
+
+uint8_t core_util_atomic_decr_u8(uint8_t * valuePtr, uint8_t delta)
+{
+    uint8_t newValue;
+    do {
+        newValue = __LDREXB((volatile uint8_t*)valuePtr) - delta;
+    } while (__STREXB(newValue, (volatile uint8_t*)valuePtr));
+    return newValue;
+}
+
+uint16_t core_util_atomic_decr_u16(uint16_t * valuePtr, uint16_t delta)
+{
+    uint16_t newValue;
+    do {
+        newValue = __LDREXH((volatile uint16_t*)valuePtr) - delta;
+    } while (__STREXH(newValue, (volatile uint16_t*)valuePtr));
+    return newValue;
+}
+
+uint32_t core_util_atomic_decr_u32(uint32_t * valuePtr, uint32_t delta)
+{
+    uint32_t newValue;
+    do {
+        newValue = __LDREXW((volatile uint32_t*)valuePtr) - delta;
+    } while (__STREXW(newValue, (volatile uint32_t*)valuePtr));
+    return newValue;
+}
+
+#else
+
+bool core_util_atomic_cas_u8(uint8_t *ptr, uint8_t *expectedCurrentValue, uint8_t desiredValue)
+{
+    bool success;
+    uint8_t currentValue;
+    core_util_critical_section_enter();
+    currentValue = *ptr;
+    if (currentValue == *expectedCurrentValue) {
+        *ptr = desiredValue;
+        success = true;
+    } else {
+        *expectedCurrentValue = currentValue;
+        success = false;
+    }
+    core_util_critical_section_exit();
+    return success;
+}
+
+bool core_util_atomic_cas_u16(uint16_t *ptr, uint16_t *expectedCurrentValue, uint16_t desiredValue)
+{
+    bool success;
+    uint16_t currentValue;
+    core_util_critical_section_enter();
+    currentValue = *ptr;
+    if (currentValue == *expectedCurrentValue) {
+        *ptr = desiredValue;
+        success = true;
+    } else {
+        *expectedCurrentValue = currentValue;
+        success = false;
+    }
+    core_util_critical_section_exit();
+    return success;
+}
+
+
+bool core_util_atomic_cas_u32(uint32_t *ptr, uint32_t *expectedCurrentValue, uint32_t desiredValue)
+{
+    bool success;
+    uint32_t currentValue;
+    core_util_critical_section_enter();
+    currentValue = *ptr;
+    if (currentValue == *expectedCurrentValue) {
+        *ptr = desiredValue;
+        success = true;
+    } else {
+        *expectedCurrentValue = currentValue;
+        success = false;
+    }
+    core_util_critical_section_exit();
+    return success;
+}
+
+uint8_t core_util_atomic_incr_u8(uint8_t * valuePtr, uint8_t delta)
+{
+    uint8_t newValue;
+    core_util_critical_section_enter();
+    newValue = *valuePtr + delta;
+    *valuePtr = newValue;
+    core_util_critical_section_exit();
+    return newValue;
+}
+
+uint16_t core_util_atomic_incr_u16(uint16_t * valuePtr, uint16_t delta)
+{
+    uint16_t newValue;
+    core_util_critical_section_enter();
+    newValue = *valuePtr + delta;
+    *valuePtr = newValue;
+    core_util_critical_section_exit();
+    return newValue;
+}
+
+uint32_t core_util_atomic_incr_u32(uint32_t * valuePtr, uint32_t delta)
+{
+    uint32_t newValue;
+    core_util_critical_section_enter();
+    newValue = *valuePtr + delta;
+    *valuePtr = newValue;
+    core_util_critical_section_exit();
+    return newValue;
+}
+
+
+uint8_t core_util_atomic_decr_u8(uint8_t * valuePtr, uint8_t delta)
+{
+    uint8_t newValue;
+    core_util_critical_section_enter();
+    newValue = *valuePtr - delta;
+    *valuePtr = newValue;
+    core_util_critical_section_exit();
+    return newValue;
+}
+
+uint16_t core_util_atomic_decr_u16(uint16_t * valuePtr, uint16_t delta)
+{
+    uint16_t newValue;
+    core_util_critical_section_enter();
+    newValue = *valuePtr - delta;
+    *valuePtr = newValue;
+    core_util_critical_section_exit();
+    return newValue;
+}
+
+uint32_t core_util_atomic_decr_u32(uint32_t * valuePtr, uint32_t delta)
+{
+    uint32_t newValue;
+    core_util_critical_section_enter();
+    newValue = *valuePtr - delta;
+    *valuePtr = newValue;
+    core_util_critical_section_exit();
+    return newValue;
+}
+
+#endif
+