1 /*

     2  * Copyright (c) 2002,2016 Mario de Sousa (msousa@fe.up.pt)

     3  *

     4  * This file is part of the Modbus library for Beremiz and matiec.

     5  *

     6  * This Modbus library is free software: you can redistribute it and/or modify

     7  * it under the terms of the GNU Lesser General Public License as published by

     8  * the Free Software Foundation, either version 3 of the License, or

     9  * (at your option) any later version.

    10  *

    11  * This program is distributed in the hope that it will be useful, but

    12  * WITHOUT ANY WARRANTY; without even the implied warranty of

    13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser 

    14  * General Public License for more details.

    15  *

    16  * You should have received a copy of the GNU Lesser General Public License

    17  * along with this Modbus library.  If not, see <http://www.gnu.org/licenses/>.

    18  *

    19  * This code is made available on the understanding that it will not be

    20  * used in safety-critical situations without a full and competent review.

    21  */

    22 

    23 

    24 

    25  /* Data structures used by the modbus protocols... */

    26 

    27 

    28 #ifndef __MODBUS_DS_UTIL_H

    29 #define __MODBUS_DS_UTIL_H

    30 

    31 

    32 #include "mb_types.h"  /* get the data types */

    33 

    34 /**************************************/

    35 /**                                  **/

    36 /** A data structure - linear buffer **/

    37 /**                                  **/

    38 /**************************************/

    39 

    40 /* An unbounded FIFO data structure.

    41  *

    42  * The user/caller writes and reads directly from the data structure's buffer,

    43  * which eliminates slow copying of bytes between the user's and the structure's

    44  * local memory.

    45  *

    46  * The data structure stores the current data linearly in a single memory array,

    47  * i.e. the current data is stored from start to finish from a low address

    48  * to a high address, and does *not* circle back to the bottom of the address

    49  * space as is usual in a circular buffer. This allows the user/caller to

    50  * pass the structure's own byte array on to other functions such as

    51  * read() and write() for file operations.

    52  *

    53  * The FIFO is implemented by allocating more memory than the maximum number

    54  * of bytes it will ever hold, and using the extra bytes at the top of the

    55  * array as the bottom data bytes are released. When we run out of extra bytes,

    56  * (actually, when the number of un-used bytes at the beginning is larger than

    57  * a configured maximum), the whole data is moved down, freeing once again the

    58  * extra bytes at the top of the array.

    59  *

    60  * Remember that we can optimize the data structure so that whenever it becomes

    61  * empty, we can reset it to start off at the bottom of the byte array, i.e. we

    62  * can set the start = end = 0; instead of simply setting the start = end, which

    63  * may point to any position in the array.

    64  *

    65  * Taking the above into consideration, it would probably be a little more efficient

    66  * to implement it as a circular buffer with an additional linearize() function

    67  * the user could call whenever (s)he required the data to be stored linearly.

    68  * Nevertheless, since it has already been implemented as a linear buffer, and since

    69  * under normal circumstances the start and end pointers will be reset to 0 quite

    70  * often (and therefore we get no additional benefit under normal circumstances),

    71  * we will leave it as it is for the time being...

    72  *

    73  *

    74  * The user is expected to call

    75  *   lb_init() -> to initialize the structure

    76  *   lb_done() -> to free the data structure's memory

    77  *

    78  * The user can store data starting off from...

    79  *   lb_free() -> pointer to address of free memory

    80  *   lb_free_count() -> number of free bytes available

    81  * and then call

    82  *   lb_data_add()

    83  * to add the data to the data structure

    84  *

    85  * Likewise, the user can read the data directly from

    86  *   lb_data() -> pointer to address of data location

    87  *   lb_free_count() -> number of data bytes available

    88  * and free the data using

    89  *   lb_data_purge()

    90  * to remove the data from the data structure

    91  */

    92 

    93 

    94 typedef struct {

    95         u8 *data;

    96         int data_size;      /* size of the *data buffer                   */

    97         int data_start;     /* offset within *data were valid data starts */

    98         int data_end;       /* offset within *data were valid data ends   */

    99         int max_data_start; /* optimization parameter! When should it be normalised? */

   100         } lb_buf_t;

   101 

   102 /* NOTE: lb = Linear Buffer */

   103 

   104 static inline u8 *lb_init(lb_buf_t *buf, int size, int max_data_start) {

   105   if (size <= 0)

   106     return NULL;

   107 

   108   if (max_data_start >= size)

   109     max_data_start = size - 1;

   110 

   111   buf->data_size  = size;

   112   buf->data_start = 0;

   113   buf->data_end   = 0;

   114   buf->max_data_start = max_data_start;

   115   buf->data = (u8 *)malloc(size);

   116   return buf->data;

   117 }

   118 

   119 static inline void lb_done(lb_buf_t *buf) {

   120   free(buf->data);

   121   buf->data = NULL;

   122 }

   123 

   124 static inline u8 *lb_normalize(lb_buf_t *buf) {

   125   return (u8 *)memmove(buf->data,

   126                        buf->data + buf->data_start,

   127                        buf->data_end - buf->data_start);

   128 }

   129 

   130 static inline u8 *lb_data(lb_buf_t *buf) {

   131   return buf->data + buf->data_start;

   132 }

   133 

   134 static inline int lb_data_count(lb_buf_t *buf) {

   135   return buf->data_end - buf->data_start;

   136 }

   137 

   138 static inline void lb_data_add(lb_buf_t *buf, int count) {

   139   if ((buf->data_end += count) >= buf->data_size)

   140     buf->data_end = buf->data_size - 1;

   141 }

   142 

   143 static inline u8 *lb_data_purge(lb_buf_t *buf, int count) {

   144   buf->data_start += count;

   145   if (buf->data_start > buf->data_end)

   146     buf->data_start = buf->data_end;

   147 

   148   if ((buf->data_end == buf->data_size) || (buf->data_start >= buf->max_data_start))

   149     return lb_normalize(buf);

   150 

   151   return buf->data + buf->data_start;

   152 }

   153 

   154 static inline void lb_data_purge_all(lb_buf_t *buf) {

   155   buf->data_start = buf->data_end = 0;

   156 }

   157 

   158 static inline u8 *lb_free(lb_buf_t *buf) {

   159   return buf->data + buf->data_end;

   160 }

   161 

   162 static inline int lb_free_count(lb_buf_t *buf) {

   163   return buf->data_size - buf->data_end;

   164 }

   165 

   166 

   167 

   168 

   169 #endif  /* __MODBUS_DS_UTIL_H */