mbed_critical.h

00001 
00002 /*
00003  * Copyright (c) 2015-2016, ARM Limited, All Rights Reserved
00004  * SPDX-License-Identifier: Apache-2.0
00005  *
00006  * Licensed under the Apache License, Version 2.0 (the "License"); you may
00007  * not use this file except in compliance with the License.
00008  * You may obtain a copy of the License at
00009  *
00010  * http://www.apache.org/licenses/LICENSE-2.0
00011  *
00012  * Unless required by applicable law or agreed to in writing, software
00013  * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
00014  * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
00015  * See the License for the specific language governing permissions and
00016  * limitations under the License.
00017  */
00018 
00019 #ifndef __MBED_UTIL_CRITICAL_H__
00020 #define __MBED_UTIL_CRITICAL_H__
00021 
00022 #include <stdbool.h>
00023 #include <stdint.h>
00024 #include <stddef.h>
00025 
00026 #ifdef __cplusplus
00027 extern "C" {
00028 #endif
00029 
00030 /** \addtogroup platform */
00031 /** @{*/
00032 /**
00033  * \defgroup platform_critical critical section function
00034  * @{
00035  */
00036 
00037 /** Determine the current interrupts enabled state
00038   *
00039   * This function can be called to determine whether or not interrupts are currently enabled.
00040   * @note
00041   * NOTE:
00042   * This function works for both cortex-A and cortex-M, although the underlyng implementation
00043   * differs.
00044   * @return true if interrupts are enabled, false otherwise
00045   */
00046 bool core_util_are_interrupts_enabled(void);
00047 
00048 /** Determine if this code is executing from an interrupt
00049   *
00050   * This function can be called to determine if the code is running on interrupt context.
00051   * @note
00052   * NOTE:
00053   * This function works for both cortex-A and cortex-M, although the underlyng implementation
00054   * differs.
00055   * @return true if in an isr, false otherwise
00056   */
00057 bool core_util_is_isr_active(void);
00058 
00059 /** Mark the start of a critical section
00060   *
00061   * This function should be called to mark the start of a critical section of code.
00062   * @note
00063   * NOTES:
00064   * 1) The use of this style of critical section is targetted at C based implementations.
00065   * 2) These critical sections can be nested.
00066   * 3) The interrupt enable state on entry to the first critical section (of a nested set, or single
00067   *    section) will be preserved on exit from the section.
00068   * 4) This implementation will currently only work on code running in privileged mode.
00069   */
00070 void core_util_critical_section_enter(void);
00071 
00072 /** Mark the end of a critical section
00073   *
00074   * This function should be called to mark the end of a critical section of code.
00075   * @note
00076   * NOTES:
00077   * 1) The use of this style of critical section is targetted at C based implementations.
00078   * 2) These critical sections can be nested.
00079   * 3) The interrupt enable state on entry to the first critical section (of a nested set, or single
00080   *    section) will be preserved on exit from the section.
00081   * 4) This implementation will currently only work on code running in privileged mode.
00082   */
00083 void core_util_critical_section_exit(void);
00084 
00085 /**
00086  * Atomic compare and set. It compares the contents of a memory location to a
00087  * given value and, only if they are the same, modifies the contents of that
00088  * memory location to a given new value. This is done as a single atomic
00089  * operation. The atomicity guarantees that the new value is calculated based on
00090  * up-to-date information; if the value had been updated by another thread in
00091  * the meantime, the write would fail due to a mismatched expectedCurrentValue.
00092  *
00093  * Refer to https://en.wikipedia.org/wiki/Compare-and-set [which may redirect
00094  * you to the article on compare-and swap].
00095  *
00096  * @param  ptr                  The target memory location.
00097  * @param[in,out] expectedCurrentValue A pointer to some location holding the
00098  *                              expected current value of the data being set atomically.
00099  *                              The computed 'desiredValue' should be a function of this current value.
00100  *                              @note: This is an in-out parameter. In the
00101  *                              failure case of atomic_cas (where the
00102  *                              destination isn't set), the pointee of expectedCurrentValue is
00103  *                              updated with the current value.
00104  * @param[in] desiredValue      The new value computed based on '*expectedCurrentValue'.
00105  *
00106  * @return                      true if the memory location was atomically
00107  *                              updated with the desired value (after verifying
00108  *                              that it contained the expectedCurrentValue),
00109  *                              false otherwise. In the failure case,
00110  *                              exepctedCurrentValue is updated with the new
00111  *                              value of the target memory location.
00112  *
00113  * pseudocode:
00114  * function cas(p : pointer to int, old : pointer to int, new : int) returns bool {
00115  *     if *p != *old {
00116  *         *old = *p
00117  *         return false
00118  *     }
00119  *     *p = new
00120  *     return true
00121  * }
00122  *
00123  * @note: In the failure case (where the destination isn't set), the value
00124  * pointed to by expectedCurrentValue is instead updated with the current value.
00125  * This property helps writing concise code for the following incr:
00126  *
00127  * function incr(p : pointer to int, a : int) returns int {
00128  *     done = false
00129  *     value = *p // This fetch operation need not be atomic.
00130  *     while not done {
00131  *         done = atomic_cas(p, &value, value + a) // *value gets updated automatically until success
00132  *     }
00133  *     return value + a
00134  * }
00135  *
00136  * @note: This corresponds to the C11 "atomic_compare_exchange_strong" - it
00137  * always succeeds if the current value is expected, as per the pseudocode
00138  * above; it will not spuriously fail as "atomic_compare_exchange_weak" may.
00139  */
00140 bool core_util_atomic_cas_u8(uint8_t *ptr, uint8_t *expectedCurrentValue, uint8_t desiredValue);
00141 
00142 /**
00143  * Atomic compare and set. It compares the contents of a memory location to a
00144  * given value and, only if they are the same, modifies the contents of that
00145  * memory location to a given new value. This is done as a single atomic
00146  * operation. The atomicity guarantees that the new value is calculated based on
00147  * up-to-date information; if the value had been updated by another thread in
00148  * the meantime, the write would fail due to a mismatched expectedCurrentValue.
00149  *
00150  * Refer to https://en.wikipedia.org/wiki/Compare-and-set [which may redirect
00151  * you to the article on compare-and swap].
00152  *
00153  * @param  ptr                  The target memory location.
00154  * @param[in,out] expectedCurrentValue A pointer to some location holding the
00155  *                              expected current value of the data being set atomically.
00156  *                              The computed 'desiredValue' should be a function of this current value.
00157  *                              @note: This is an in-out parameter. In the
00158  *                              failure case of atomic_cas (where the
00159  *                              destination isn't set), the pointee of expectedCurrentValue is
00160  *                              updated with the current value.
00161  * @param[in] desiredValue      The new value computed based on '*expectedCurrentValue'.
00162  *
00163  * @return                      true if the memory location was atomically
00164  *                              updated with the desired value (after verifying
00165  *                              that it contained the expectedCurrentValue),
00166  *                              false otherwise. In the failure case,
00167  *                              exepctedCurrentValue is updated with the new
00168  *                              value of the target memory location.
00169  *
00170  * pseudocode:
00171  * function cas(p : pointer to int, old : pointer to int, new : int) returns bool {
00172  *     if *p != *old {
00173  *         *old = *p
00174  *         return false
00175  *     }
00176  *     *p = new
00177  *     return true
00178  * }
00179  *
00180  * @note: In the failure case (where the destination isn't set), the value
00181  * pointed to by expectedCurrentValue is instead updated with the current value.
00182  * This property helps writing concise code for the following incr:
00183  *
00184  * function incr(p : pointer to int, a : int) returns int {
00185  *     done = false
00186  *     value = *p // This fetch operation need not be atomic.
00187  *     while not done {
00188  *         done = atomic_cas(p, &value, value + a) // *value gets updated automatically until success
00189  *     }
00190  *     return value + a
00191  * }
00192  *
00193  * @note: This corresponds to the C11 "atomic_compare_exchange_strong" - it
00194  * always succeeds if the current value is expected, as per the pseudocode
00195  * above; it will not spuriously fail as "atomic_compare_exchange_weak" may.
00196  */
00197 bool core_util_atomic_cas_u16(uint16_t *ptr, uint16_t *expectedCurrentValue, uint16_t desiredValue);
00198 
00199 /**
00200  * Atomic compare and set. It compares the contents of a memory location to a
00201  * given value and, only if they are the same, modifies the contents of that
00202  * memory location to a given new value. This is done as a single atomic
00203  * operation. The atomicity guarantees that the new value is calculated based on
00204  * up-to-date information; if the value had been updated by another thread in
00205  * the meantime, the write would fail due to a mismatched expectedCurrentValue.
00206  *
00207  * Refer to https://en.wikipedia.org/wiki/Compare-and-set [which may redirect
00208  * you to the article on compare-and swap].
00209  *
00210  * @param  ptr                  The target memory location.
00211  * @param[in,out] expectedCurrentValue A pointer to some location holding the
00212  *                              expected current value of the data being set atomically.
00213  *                              The computed 'desiredValue' should be a function of this current value.
00214  *                              @note: This is an in-out parameter. In the
00215  *                              failure case of atomic_cas (where the
00216  *                              destination isn't set), the pointee of expectedCurrentValue is
00217  *                              updated with the current value.
00218  * @param[in] desiredValue      The new value computed based on '*expectedCurrentValue'.
00219  *
00220  * @return                      true if the memory location was atomically
00221  *                              updated with the desired value (after verifying
00222  *                              that it contained the expectedCurrentValue),
00223  *                              false otherwise. In the failure case,
00224  *                              exepctedCurrentValue is updated with the new
00225  *                              value of the target memory location.
00226  *
00227  * pseudocode:
00228  * function cas(p : pointer to int, old : pointer to int, new : int) returns bool {
00229  *     if *p != *old {
00230  *         *old = *p
00231  *         return false
00232  *     }
00233  *     *p = new
00234  *     return true
00235  * }
00236  *
00237  * @note: In the failure case (where the destination isn't set), the value
00238  * pointed to by expectedCurrentValue is instead updated with the current value.
00239  * This property helps writing concise code for the following incr:
00240  *
00241  * function incr(p : pointer to int, a : int) returns int {
00242  *     done = false
00243  *     value = *p // This fetch operation need not be atomic.
00244  *     while not done {
00245  *         done = atomic_cas(p, &value, value + a) // *value gets updated automatically until success
00246  *     }
00247  *     return value + a
00248  *
00249  * @note: This corresponds to the C11 "atomic_compare_exchange_strong" - it
00250  * always succeeds if the current value is expected, as per the pseudocode
00251  * above; it will not spuriously fail as "atomic_compare_exchange_weak" may.
00252  * }
00253  */
00254 bool core_util_atomic_cas_u32(uint32_t *ptr, uint32_t *expectedCurrentValue, uint32_t desiredValue);
00255 
00256 /**
00257  * Atomic compare and set. It compares the contents of a memory location to a
00258  * given value and, only if they are the same, modifies the contents of that
00259  * memory location to a given new value. This is done as a single atomic
00260  * operation. The atomicity guarantees that the new value is calculated based on
00261  * up-to-date information; if the value had been updated by another thread in
00262  * the meantime, the write would fail due to a mismatched expectedCurrentValue.
00263  *
00264  * Refer to https://en.wikipedia.org/wiki/Compare-and-set [which may redirect
00265  * you to the article on compare-and swap].
00266  *
00267  * @param  ptr                  The target memory location.
00268  * @param[in,out] expectedCurrentValue A pointer to some location holding the
00269  *                              expected current value of the data being set atomically.
00270  *                              The computed 'desiredValue' should be a function of this current value.
00271  *                              @note: This is an in-out parameter. In the
00272  *                              failure case of atomic_cas (where the
00273  *                              destination isn't set), the pointee of expectedCurrentValue is
00274  *                              updated with the current value.
00275  * @param[in] desiredValue      The new value computed based on '*expectedCurrentValue'.
00276  *
00277  * @return                      true if the memory location was atomically
00278  *                              updated with the desired value (after verifying
00279  *                              that it contained the expectedCurrentValue),
00280  *                              false otherwise. In the failure case,
00281  *                              exepctedCurrentValue is updated with the new
00282  *                              value of the target memory location.
00283  *
00284  * pseudocode:
00285  * function cas(p : pointer to int, old : pointer to int, new : int) returns bool {
00286  *     if *p != *old {
00287  *         *old = *p
00288  *         return false
00289  *     }
00290  *     *p = new
00291  *     return true
00292  * }
00293  *
00294  * @note: In the failure case (where the destination isn't set), the value
00295  * pointed to by expectedCurrentValue is instead updated with the current value.
00296  * This property helps writing concise code for the following incr:
00297  *
00298  * function incr(p : pointer to int, a : int) returns int {
00299  *     done = false
00300  *     value = *p // This fetch operation need not be atomic.
00301  *     while not done {
00302  *         done = atomic_cas(p, &value, value + a) // *value gets updated automatically until success
00303  *     }
00304  *     return value + a
00305  * }
00306  *
00307  * @note: This corresponds to the C11 "atomic_compare_exchange_strong" - it
00308  * always succeeds if the current value is expected, as per the pseudocode
00309  * above; it will not spuriously fail as "atomic_compare_exchange_weak" may.
00310  */
00311 bool core_util_atomic_cas_ptr(void **ptr, void **expectedCurrentValue, void *desiredValue);
00312 
00313 /**
00314  * Atomic increment.
00315  * @param  valuePtr Target memory location being incremented.
00316  * @param  delta    The amount being incremented.
00317  * @return          The new incremented value.
00318  */
00319 uint8_t core_util_atomic_incr_u8(uint8_t *valuePtr, uint8_t delta);
00320 
00321 /**
00322  * Atomic increment.
00323  * @param  valuePtr Target memory location being incremented.
00324  * @param  delta    The amount being incremented.
00325  * @return          The new incremented value.
00326  */
00327 uint16_t core_util_atomic_incr_u16(uint16_t *valuePtr, uint16_t delta);
00328 
00329 /**
00330  * Atomic increment.
00331  * @param  valuePtr Target memory location being incremented.
00332  * @param  delta    The amount being incremented.
00333  * @return          The new incremented value.
00334  */
00335 uint32_t core_util_atomic_incr_u32(uint32_t *valuePtr, uint32_t delta);
00336 
00337 /**
00338  * Atomic increment.
00339  * @param  valuePtr Target memory location being incremented.
00340  * @param  delta    The amount being incremented in bytes.
00341  * @return          The new incremented value.
00342  *
00343  * @note The type of the pointer argument is not taken into account
00344  *       and the pointer is incremented by bytes.
00345  */
00346 void *core_util_atomic_incr_ptr(void **valuePtr, ptrdiff_t delta);
00347 
00348 /**
00349  * Atomic decrement.
00350  * @param  valuePtr Target memory location being decremented.
00351  * @param  delta    The amount being decremented.
00352  * @return          The new decremented value.
00353  */
00354 uint8_t core_util_atomic_decr_u8(uint8_t *valuePtr, uint8_t delta);
00355 
00356 /**
00357  * Atomic decrement.
00358  * @param  valuePtr Target memory location being decremented.
00359  * @param  delta    The amount being decremented.
00360  * @return          The new decremented value.
00361  */
00362 uint16_t core_util_atomic_decr_u16(uint16_t *valuePtr, uint16_t delta);
00363 
00364 /**
00365  * Atomic decrement.
00366  * @param  valuePtr Target memory location being decremented.
00367  * @param  delta    The amount being decremented.
00368  * @return          The new decremented value.
00369  */
00370 uint32_t core_util_atomic_decr_u32(uint32_t *valuePtr, uint32_t delta);
00371 
00372 /**
00373  * Atomic decrement.
00374  * @param  valuePtr Target memory location being decremented.
00375  * @param  delta    The amount being decremented in bytes.
00376  * @return          The new decremented value.
00377  *
00378  * @note The type of the pointer argument is not taken into account
00379  *       and the pointer is decremented by bytes
00380  */
00381 void *core_util_atomic_decr_ptr(void **valuePtr, ptrdiff_t delta);
00382 
00383 #ifdef __cplusplus
00384 } // extern "C"
00385 #endif
00386 /**@}*/
00387 
00388 /**@}*/
00389 
00390 #endif // __MBED_UTIL_CRITICAL_H__
00391 
00392 
00393