Projects/USBtoSerial/Lib/LightweightRingBuff.h

   1 /*
   2              LUFA Library
   3      Copyright (C) Dean Camera, 2010.
   4
   5   dean [at] fourwalledcubicle [dot] com
   6       www.fourwalledcubicle.com
   7 */
   8
   9 /*
  10   Copyright 2010  Dean Camera (dean [at] fourwalledcubicle [dot] com)
  11
  12   Permission to use, copy, modify, distribute, and sell this
  13   software and its documentation for any purpose is hereby granted
  14   without fee, provided that the above copyright notice appear in
  15   all copies and that both that the copyright notice and this
  16   permission notice and warranty disclaimer appear in supporting
  17   documentation, and that the name of the author not be used in
  18   advertising or publicity pertaining to distribution of the
  19   software without specific, written prior permission.
  20
  21   The author disclaim all warranties with regard to this
  22   software, including all implied warranties of merchantability
  23   and fitness.  In no event shall the author be liable for any
  24   special, indirect or consequential damages or any damages
  25   whatsoever resulting from loss of use, data or profits, whether
  26   in an action of contract, negligence or other tortious action,
  27   arising out of or in connection with the use or performance of
  28   this software.
  29 */
  30
  31 /** \file
  32  *
  33  *  Ultra lightweight ring buffer, for fast insertion/deletion. This uses inlined functions
  34  *  for maximum speed. All buffers created with this library must be of the same size, however
  35  *  multiple independant buffers can be created.
  36  *
  37  *  Note that for each buffer, insertion and removal operations may occur at the same time (via
  38  *  a multithreaded ISR based system) however the same kind of operation (two or more insertions
  39  *  or deletions) must not overlap. If there is possibility of two or more of the same kind of
  40  *  operating occuring at the same point in time, atomic (mutex) locking should be used.
  41  */
  42
  43 #ifndef _ULW_RING_BUFF_H_
  44 #define _ULW_RING_BUFF_H_
  45
  46         /* Includes: */
  47                 #include <util/atomic.h>
  48
  49                 #include <stdint.h>
  50                 #include <stdbool.h>
  51
  52         /* Defines: */
  53                 /** Size of each ring buffer, in data elements - must be between 1 and 255. */
  54                 #define BUFFER_SIZE         255
  55
  56                 /** Type of data to store into the buffer. */
  57                 #define RingBuff_Data_t     uint8_t
  58
  59                 /** Datatype which may be used to store the count of data stored in a buffer, retrieved
  60                  *  via a call to \ref RingBuffer_GetCount().
  61                  */
  62                 #if (BUFFER_SIZE <= 0xFF)
  63                         #define RingBuff_Count_t   uint8_t
  64                 #else
  65                         #define RingBuff_Count_t   uint16_t
  66                 #endif
  67
  68         /* Type Defines: */
  69                 /** Type define for a new ring buffer object. Buffers should be initialized via a call to
  70                  *  \ref RingBuffer_InitBuffer() before use.
  71                  */
  72                 typedef struct
  73                 {
  74                         RingBuff_Data_t  Buffer[BUFFER_SIZE]; /**< Internal ring buffer data, referenced by the buffer pointers. */
  75                         RingBuff_Data_t* In; /**< Current storage location in the circular buffer */
  76                         RingBuff_Data_t* Out; /**< Current retrieval location in the circular buffer */
  77                         RingBuff_Count_t Count;
  78                 } RingBuff_t;
  79
  80         /* Inline Functions: */
  81                 /** Initializes a ring buffer ready for use. Buffers must be initialized via this function
  82                  *  before any operations are called upon them. Already initialized buffers may be reset
  83                  *  by re-initializing them using this function.
  84                  *
  85                  *  \param[out] Buffer  Pointer to a ring buffer structure to initialize
  86                  */
  87                 static inline void RingBuffer_InitBuffer(RingBuff_t* const Buffer)
  88                 {
  89                         ATOMIC_BLOCK(ATOMIC_RESTORESTATE)
  90                         {
  91                                 Buffer->In  = Buffer->Buffer;
  92                                 Buffer->Out = Buffer->Buffer;
  93                         }
  94                 }
  95
  96                 /** Retrieves the minimum number of bytes stored in a particular buffer. This value is computed
  97                  *  by entering an atomic lock on the buffer while the IN and OUT locations are fetched, so that
  98                  *  the buffer cannot be modified while the computation takes place. This value should be cached
  99                  *  when reading out the contents of the buffer, so that as small a time as possible is spent
 100                  *  in an atomic lock.
 101                  *
 102                  *  \note The value returned by this function is guaranteed to only be the minimum number of bytes
 103                  *        stored in the given buffer; this value may change as other threads write new data and so
 104                  *        the returned number should be used only to determine how many successive reads may safely
 105                  *        be performed on the buffer.
 106                  *
 107                  *  \param[in] Buffer  Pointer to a ring buffer structure whose count is to be computed
 108                  */
 109                 static inline RingBuff_Count_t RingBuffer_GetCount(RingBuff_t* const Buffer)
 110                 {
 111                         RingBuff_Count_t Count;
 112
 113                         ATOMIC_BLOCK(ATOMIC_RESTORESTATE)
 114                         {
 115                                 Count = Buffer->Count;
 116                         }
 117
 118                         return Count;
 119                 }
 120
 121                 /** Atomically determines if the specified ring buffer contains any free space. This should
 122                  *  be tested before storing data to the buffer, to ensure that no data is lost due to a
 123                  *  buffer overrun.
 124                  *
 125                  *  \param[in,out] Buffer  Pointer to a ring buffer structure to insert into
 126                  *
 127                  *  \return Boolean true if the buffer contains no free space, false otherwise
 128                  */
 129                 static inline bool RingBuffer_IsFull(RingBuff_t* const Buffer)
 130                 {
 131                         return (RingBuffer_GetCount(Buffer) == BUFFER_SIZE);
 132                 }
 133
 134                 /** Atomically determines if the specified ring buffer contains any data. This should
 135                  *  be tested before removing data from the buffer, to ensure that the buffer does not
 136                  *  underflow.
 137                  *
 138                  *  If the data is to be removed in a loop, store the total number of bytes stored in the
 139                  *  buffer (via a call to the \ref RingBuffer_GetCount() function) in a temporary variable
 140                  *  to reduce the time spent in atomicity locks.
 141                  *
 142                  *  \param[in,out] Buffer  Pointer to a ring buffer structure to insert into
 143                  *
 144                  *  \return Boolean true if the buffer contains no free space, false otherwise
 145                  */
 146                 static inline bool RingBuffer_IsEmpty(RingBuff_t* const Buffer)
 147                 {
 148                         return (RingBuffer_GetCount(Buffer) == 0);
 149                 }
 150
 151                 /** Inserts an element into the ring buffer.
 152                  *
 153                  *  \note Only one execution thread (main program thread or an ISR) may insert into a single buffer
 154                  *        otherwise data corruption may occur. Insertion and removal may occur from different execution
 155                  *        threads.
 156                  *
 157                  *  \param[in,out] Buffer  Pointer to a ring buffer structure to insert into
 158                  *  \param[in]     Data    Data element to insert into the buffer
 159                  */
 160                 static inline void RingBuffer_Insert(RingBuff_t* const Buffer,
 161                                                      const RingBuff_Data_t Data)
 162                 {
 163                         *Buffer->In = Data;
 164
 165                         if (++Buffer->In == &Buffer->Buffer[BUFFER_SIZE])
 166                           Buffer->In = Buffer->Buffer;
 167
 168                         ATOMIC_BLOCK(ATOMIC_RESTORESTATE)
 169                         {
 170                                 Buffer->Count++;
 171                         }
 172                 }
 173
 174                 /** Removes an element from the ring buffer.
 175                  *
 176                  *  \note Only one execution thread (main program thread or an ISR) may remove from a single buffer
 177                  *        otherwise data corruption may occur. Insertion and removal may occur from different execution
 178                  *        threads.
 179                  *
 180                  *  \param[in,out] Buffer  Pointer to a ring buffer structure to retrieve from
 181                  *
 182                  *  \return Next data element stored in the buffer
 183                  */
 184                 static inline RingBuff_Data_t RingBuffer_Remove(RingBuff_t* const Buffer)
 185                 {
 186                         RingBuff_Data_t Data = *Buffer->Out;
 187
 188                         if (++Buffer->Out == &Buffer->Buffer[BUFFER_SIZE])
 189                           Buffer->Out = Buffer->Buffer;
 190
 191                         ATOMIC_BLOCK(ATOMIC_RESTORESTATE)
 192                         {
 193                                 Buffer->Count--;
 194                         }
 195
 196                         return Data;
 197                 }
 198
 199 #endif
 200