Mbed OS Reference | CircularBuffer.h Source File

 /* mbed Microcontroller Library
  * Copyright (c) 2015-2019 ARM Limited
  * 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_CIRCULARBUFFER_H
 #define MBED_CIRCULARBUFFER_H
 
 #include <stdint.h>
 #include "platform/mbed_critical.h"
 #include "platform/mbed_assert.h"
 #include "platform/Span.h"
 #include "platform/mbed_atomic.h"
 
 namespace mbed {
 
 namespace internal {
 /* Detect if CounterType of the Circular buffer is of unsigned type. */
 template<typename T>
 struct is_unsigned {
     static const bool value = false;
 };
 template<>
 struct is_unsigned<unsigned char> {
     static const bool value = true;
 };
 template<>
 struct is_unsigned<unsigned short> {
     static const bool value = true;
 };
 template<>
 struct is_unsigned<unsigned int> {
     static const bool value = true;
 };
 template<>
 struct is_unsigned<unsigned long> {
     static const bool value = true;
 };
 template<>
 struct is_unsigned<unsigned long long> {
     static const bool value = true;
 };
 }
 
 /** \addtogroup platform-public-api */
 /** @{*/
 /**
  * \defgroup platform_CircularBuffer CircularBuffer functions
  * @{
  */
 
 /** Templated Circular buffer class
  *
  *  @note Synchronization level: Interrupt safe.
  *  @note CounterType must be unsigned and consistent with BufferSize.
  */
 template<typename T, uint32_t BufferSize, typename CounterType = uint32_t>
 class CircularBuffer {
 public:
     CircularBuffer() : _head(0), _tail(0), _full(false)
     {
         MBED_STATIC_ASSERT(
             internal::is_unsigned<CounterType>::value,
             "CounterType must be unsigned"
         );
 
         MBED_STATIC_ASSERT(
             (sizeof(CounterType) >= sizeof(uint32_t)) ||
             (BufferSize < (((uint64_t) 1) << (sizeof(CounterType) * 8))),
             "Invalid BufferSize for the CounterType"
         );
     }
 
     ~CircularBuffer()
     {
     }
 
     /** Push the transaction to the buffer. This overwrites the buffer if it's full.
      *
      * @param data Data to be pushed to the buffer.
      */
     void push(const T &data)
     {
         core_util_critical_section_enter();
 
         _buffer[_head] = data;
 
         _head = incrementCounter(_head);
 
         if (_full) {
             _tail = _head;
         } else if (_head == _tail) {
             _full = true;
         }
 
         core_util_critical_section_exit();
     }
 
     /** Push the transaction to the buffer. This overwrites the buffer if it's full.
      *
      * @param src Data to be pushed to the buffer.
      * @param len Number of items to be pushed to the buffer.
      */
     void push(const T *src, CounterType len)
     {
         MBED_ASSERT(len > 0);
 
         core_util_critical_section_enter();
 
         /* if we try to write more bytes than the buffer can hold we only bother writing the last bytes */
         if (len > BufferSize) {
             _tail = 0;
             _head = 0;
             _full = true;
             std::copy(src + len - BufferSize, src + len, _buffer);
         } else {
             /* we need to adjust the tail at the end if we're filling the buffer of overflowing */
             bool adjust_tail = ((BufferSize - non_critical_size()) <= len);
 
             CounterType written = len;
 
             /* on first pass we write as much as we can to the right of head */
             if ((_head + written) > BufferSize) {
                 written = BufferSize - _head;
             }
 
             std::copy(src, src + written, _buffer + _head);
             _head = incrementCounter(_head, written);
 
             CounterType left_to_write = len - written;
 
             /* we might need to continue to write from the start of the buffer */
             if (left_to_write) {
                 std::copy(src + written, src + written + left_to_write, _buffer);
                 _head = left_to_write;
             }
 
             if (adjust_tail) {
                 _tail = _head;
                 _full = true;
             }
         }
 
         core_util_critical_section_exit();
     }
 
     /** Push the transaction to the buffer. This overwrites the buffer if it's full.
      *
      * @param src Data to be pushed to the buffer.
      */
     void push(mbed::Span<const T> src)
     {
         push(src.data(), src.size());
     }
 
     /** Pop from the buffer.
      *
      * @param data Container to store the data to be popped from the buffer.
      * @return True if data popped.
      */
     bool pop(T &data)
     {
         bool data_popped = false;
 
         core_util_critical_section_enter();
 
         if (!non_critical_empty()) {
             data_popped = true;
 
             data = _buffer[_tail];
             _tail = incrementCounter(_tail);
             _full = false;
         }
 
         core_util_critical_section_exit();
 
         return data_popped;
     }
 
     /**
      * Pop multiple elements from the buffer.
      *
      * @param dest The array which will receive the elements.
      * @param len The number of elements to pop.
      *
      * @return The number of elements popped.
      */
     CounterType pop(T *dest, CounterType len)
     {
         MBED_ASSERT(len > 0);
 
         if (len == 0) {
             return 0;
         }
 
         CounterType data_popped = 0;
 
         core_util_critical_section_enter();
 
         if (!non_critical_empty()) {
             /* make sure we only try to read as much as we have items present */
             if (len > non_critical_size()) {
                 len = non_critical_size();
             }
             data_popped = len;
 
             /* items may be split by overlap, take only the number we have to the right of tail */
             if ((_tail + data_popped) > BufferSize) {
                 data_popped = BufferSize - _tail;
             }
 
             std::copy(_buffer + _tail, _buffer + _tail + data_popped, dest);
             _tail = incrementCounter(_tail, data_popped);
 
             /* if we looped over the end we may need to pop again */
             CounterType left_to_pop = len - data_popped;
 
             if (left_to_pop) {
                 std::copy(_buffer, _buffer + left_to_pop, dest + data_popped);
                 _tail = left_to_pop;
 
                 data_popped += left_to_pop;
             }
 
             _full = false;
         }
 
         core_util_critical_section_exit();
 
         return data_popped;
     }
 
     /**
      * Pop multiple elements from the buffer.
      *
      * @param dest The span that contains the buffer that will be used to store the elements.
      *
      * @return The span with the size set to number of elements popped using the buffer passed in as the parameter.
      */
     mbed::Span<T> pop(mbed::Span<T> dest)
     {
         CounterType popped = pop(dest.data(), dest.size());
         return mbed::make_Span(dest.data(), popped);
     }
 
     /** Check if the buffer is empty.
      *
      * @return True if the buffer is empty, false if not.
      */
     bool empty() const
     {
         core_util_critical_section_enter();
         bool is_empty = non_critical_empty();
         core_util_critical_section_exit();
         return is_empty;
     }
 
     /** Check if the buffer is full.
      *
      * @return True if the buffer is full, false if not
      */
     bool full() const
     {
         return core_util_atomic_load_bool(&_full);
     }
 
     /**
      * Reset the buffer.
      */
     void reset()
     {
         core_util_critical_section_enter();
         _head = 0;
         _tail = 0;
         _full = false;
         core_util_critical_section_exit();
     }
 
     /**
      * Get the number of elements currently stored in the circular_buffer.
      */
     CounterType size() const
     {
         core_util_critical_section_enter();
         CounterType elements = non_critical_size();
         core_util_critical_section_exit();
         return elements;
     }
 
     /** Peek into circular buffer without popping.
      *
      * @param data Data to be peeked from the buffer.
      * @return True if the buffer is not empty and data contains a transaction, false otherwise.
      */
     bool peek(T &data) const
     {
         bool data_updated = false;
         core_util_critical_section_enter();
         if (!empty()) {
             data = _buffer[_tail];
             data_updated = true;
         }
         core_util_critical_section_exit();
         return data_updated;
     }
 
 private:
     bool non_critical_empty() const
     {
         bool is_empty = (_head == _tail) && !_full;
         return is_empty;
     }
 
     CounterType non_critical_size() const
     {
         CounterType elements;
         if (!_full) {
             if (_head < _tail) {
                 elements = BufferSize + _head - _tail;
             } else {
                 elements = _head - _tail;
             }
         } else {
             elements = BufferSize;
         }
         return elements;
     }
 
     /** Used to increment _tail or _head by a given value.
      *
      * @param val The value of the counter to be incremented.
      * @param increment The amount to be added, the value after this incremented must not exceed BufferSize.
      * @return The new value of the counter.
      */
     CounterType incrementCounter(CounterType val, CounterType increment = 1)
     {
         val += increment;
 
         MBED_ASSERT(val <= BufferSize);
 
         if (val == BufferSize) {
             val = 0;
         }
 
         return val;
     }
 
 private:
     T _buffer[BufferSize];
     CounterType _head;
     CounterType _tail;
     bool _full;
 };
 
 /**@}*/
 
 /**@}*/
 
 }
 
 #endif
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