14.ring buffer

https://zhuanlan.zhihu.com/p/534098236

某个版本的ring buffer最新代码中已经废弃，逻辑比较清晰，写索引与读索引一直在自加，分别除以数据块数量取余得到环形缓冲区的位置。估计是因为除法牺牲效率，所以被作者废弃。

ringbuf.h

/**************************************************************************
*
* Copyright (C) 2012 Steve Karg <skarg@users.sourceforge.net>
*
* Permission is hereby granted, free of charge, to any person obtaining
* a copy of this software and associated documentation files (the
* "Software"), to deal in the Software without restriction, including
* without limitation the rights to use, copy, modify, merge, publish,
* distribute, sublicense, and/or sell copies of the Software, and to
* permit persons to whom the Software is furnished to do so, subject to
* the following conditions:
*
* The above copyright notice and this permission notice shall be included
* in all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
* IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
* CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
* TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
*********************************************************************/
#ifndef RINGBUF_H
#define RINGBUF_H

/* Functional Description: Generic ring buffer library for deeply
   embedded system. See the unit tests for usage examples. */

#include <stdint.h>
#include <stdbool.h>

//ring buffer 结构体
struct ring_buffer_t {
    volatile uint8_t *buffer;   /* block of memory or array of data */	//缓冲区开始地址
    unsigned element_size;      /* how many bytes for each chunk */			//缓冲区数据块的大小
    unsigned element_count;     /* number of chunks of data */					//缓冲区数据块的数量
    volatile unsigned head;     /* where the writes go */								//写索引号
    volatile unsigned tail;     /* where the reads come from */					//读索引号
};

typedef struct ring_buffer_t RING_BUFFER;

#ifdef __cplusplus
extern "C" {
#endif /* __cplusplus */

    unsigned Ringbuf_Count(RING_BUFFER const *b);											//Ringbuff已使用的数据块数量
    bool Ringbuf_Full(RING_BUFFER const *b);													//判断Ringbuff是否为满
    bool Ringbuf_Empty(RING_BUFFER const *b);													//判断Ringbuff是否为空
    volatile uint8_t *Ringbuf_Peek(RING_BUFFER const *b);							//Ringbuff下一待读取数据块指针
    bool Ringbuf_Pop(RING_BUFFER * b, uint8_t * data_element);				//从Ringbuff中取出数据块,并删除
    bool Ringbuf_Put(RING_BUFFER * b, uint8_t * data_element); 				//往Ringbuff中添加数据块
    bool Ringbuf_Put_Front(RING_BUFFER * b, uint8_t * data_element);	//往Ringbuff的头部添加数据块
    volatile uint8_t *Ringbuf_Data_Peek(RING_BUFFER * b);							//Ringbuff下一待写入数据块指针
    bool Ringbuf_Data_Put(RING_BUFFER * b, volatile uint8_t *data_element);		//
    /* Note: element_count must be a power of two */
    void Ringbuf_Init(RING_BUFFER * b,  /* ring buffer structure */									//缓冲区结构体
        volatile uint8_t * buffer,      /* data block or array of data */						//缓冲区开始地址
        unsigned element_size,  				/* size of one element in the data block */	//缓冲区数据块的大小
        unsigned element_count);        /* number of elements in the data block */	//缓冲区数据块的数量

#ifdef TEST
#include "ctest.h"
    void testRingBufSize16(
        Test * pTest);
    void testRingBufSize32(
        Test * pTest);
#endif

#ifdef __cplusplus
}
#endif /* __cplusplus */
#endif

ringbuf.c

/*####COPYRIGHTBEGIN####
 -------------------------------------------
 Copyright (C) 2008 by Steve Karg

 This program is free software; you can redistribute it and/or
 modify it under the terms of the GNU General Public License
 as published by the Free Software Foundation; either version 2
 of the License, or (at your option) any later version.

 This program is distributed in the hope that it will be useful,
 but WITHOUT ANY WARRANTY; without even the implied warranty of
 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 GNU General Public License for more details.

 You should have received a copy of the GNU General Public License
 along with this program; if not, write to:
 The Free Software Foundation, Inc.
 59 Temple Place - Suite 330
 Boston, MA  02111-1307
 USA.

 As a special exception, if other files instantiate templates or
 use macros or inline functions from this file, or you compile
 this file and link it with other works to produce a work based
 on this file, this file does not by itself cause the resulting
 work to be covered by the GNU General Public License. However
 the source code for this file must still be made available in
 accordance with section (3) of the GNU General Public License.

 This exception does not invalidate any other reasons why a work
 based on this file might be covered by the GNU General Public
 License.
 -------------------------------------------
####COPYRIGHTEND####*/

/* Functional Description: Generic ring buffer library for deeply
   embedded system. See the unit tests for usage examples. */

#include <stddef.h>
#include <stdbool.h>
#include <stdint.h>
#include "ringbuf.h"

/****************************************************************************
* DESCRIPTION: Returns the number of elements in the ring buffer
* RETURN:      Number of elements in the ring buffer
* ALGORITHM:   none
* NOTES:       none
*****************************************************************************/
unsigned Ringbuf_Count(RING_BUFFER const *b)
{
    unsigned head, tail;        /* used to avoid volatile decision */

    if (b) 
		{
        head = b->head;
        tail = b->tail;
        return head - tail;		//返回 目前缓冲区已使用的数据块数量=写索引-读索引
    }

    return 0;
}

/****************************************************************************
* DESCRIPTION: Returns the empty/full status of the ring buffer
* RETURN:      true if the ring buffer is full, false if it is not.
* ALGORITHM:   none
* NOTES:       none
*****************************************************************************/
bool Ringbuf_Full(RING_BUFFER const *b)
{		//判断 目前缓冲区已使用的数据块数量?=缓冲区数据块数量		返回1
    return (b ? (Ringbuf_Count(b) == b->element_count) : true);	
}

/****************************************************************************
* DESCRIPTION: Returns the empty/full status of the ring buffer
* RETURN:      true if the ring buffer is empty, false if it is not.
* ALGORITHM:   none
* NOTES:       none
*****************************************************************************/
bool Ringbuf_Empty(RING_BUFFER const *b)
{		//判断 目前缓冲区已使用的数据块数量?=0		返回1
    return (b ? (Ringbuf_Count(b) == 0) : true);
}

/****************************************************************************
* DESCRIPTION: Looks at the data from the front of the list without removing it
* RETURN:      pointer to the data, or NULL if nothing in the list
* ALGORITHM:   none
* NOTES:       none
*****************************************************************************/
volatile uint8_t *Ringbuf_Peek(RING_BUFFER const *b)
{
    volatile uint8_t *data_element = NULL;      /* return value */

    if (!Ringbuf_Empty(b))
		{		//从当前读索引号读取数据块指针
        data_element = b->buffer;
        data_element += ((b->tail % b->element_count) * b->element_size);
    }

    return data_element;
}

/****************************************************************************
* DESCRIPTION: Copy the data from the front of the list, and removes it
* RETURN:      true if data was copied, false if list is empty
* ALGORITHM:   none
* NOTES:       none
*****************************************************************************/
bool Ringbuf_Pop(RING_BUFFER * b, uint8_t * data_element)
{
    bool status = false;        					/* return value */
    volatile uint8_t *ring_data = NULL; 	/* used to help point ring data */
    unsigned i;														/* loop counter */

    if (!Ringbuf_Empty(b))
		{		//从当前读索引号读取数据块指针
        ring_data = b->buffer;
        ring_data += ((b->tail % b->element_count) * b->element_size);
        if (data_element)
				{		//从当前读索引号读取数据块
            for (i = 0; i < b->element_size; i++)
						{
                data_element[i] = ring_data[i];
            }
        }
        b->tail++;		//读索引号++，相当于删除已读数据块
        status = true;
    }

    return status;
}

/****************************************************************************
* DESCRIPTION: Adds an element of data to the end of the ring buffer
* RETURN:      true on succesful add, false if not added
* ALGORITHM:   none
* NOTES:       none
*****************************************************************************/
bool Ringbuf_Put(RING_BUFFER * b, uint8_t * data_element)
{
    bool status = false;        				/* return value */
    volatile uint8_t *ring_data = NULL; /* used to help point ring data */
    unsigned i; 												/* loop counter */

    if (b && data_element)
		{
        /* limit the amount of elements that we accept */
        if (!Ringbuf_Full(b))
				{		//从当前写索引号读取数据块指针
            ring_data = b->buffer;
            ring_data += ((b->head % b->element_count) * b->element_size);
            for (i = 0; i < b->element_size; i++)
						{		//从当前写索引号写入数据块
                ring_data[i] = data_element[i];
            }
            b->head++;		//写索引号++，以便指向下一空数据块地址
            status = true;
        }
    }

    return status;
}

/****************************************************************************
* DESCRIPTION: Adds an element of data to the front of the ring buffer
* RETURN:      true on succesful add, false if not added
* ALGORITHM:   none
* NOTES:       moves the tail on add instead of head, so this function
*              can't be used if keeping producer and consumer
*              as separate processes (i.e. interrupts)
*****************************************************************************/
bool Ringbuf_Put_Front(RING_BUFFER * b, uint8_t * data_element)
{
    bool status = false;        				/* return value */
    volatile uint8_t *ring_data = NULL; /* used to help point ring data */
    unsigned i = 0;     								/* loop counter */

    if (b && data_element)
		{
        /* limit the amount of elements that we accept */
        if (!Ringbuf_Full(b))
				{		//读索引号-1，读取数据块指针
            b->tail--;
            ring_data = b->buffer;
            ring_data += ((b->tail % b->element_count) * b->element_size);
            /* copy the data to the ring data element */
            for (i = 0; i < b->element_size; i++)
						{		//从当前-1后的读索引号写入数据块，相当于插入数据到读队列头部
                ring_data[i] = data_element[i];
            }
            status = true;
        }
    }

    return status;
}

/****************************************************************************
* DESCRIPTION: Gets a pointer to the next free data element of the buffer
*              without adding it to the ring.
* RETURN:      pointer to the next data chunk, or NULL if ring buffer is full.
* ALGORITHM:   none
* NOTES:       Use Ringbuf_Data_Peek with Ringbuf_Data_Put
*****************************************************************************/
volatile uint8_t *Ringbuf_Data_Peek(RING_BUFFER * b)
{
    volatile uint8_t *ring_data = NULL; /* used to help point ring data */

    if (b)
		{
        /* limit the amount of elements that we accept */
        if (!Ringbuf_Full(b))
				{		//从当前写索引号读取数据块指针
            ring_data = b->buffer;
            ring_data += ((b->head % b->element_count) * b->element_size);
        }
    }

    return ring_data;
}

/****************************************************************************
* DESCRIPTION: Adds the previously peeked element of data to the end of the
*              ring buffer
* RETURN:      true if the buffer has space and the data element points to the
*              same memory previously peeked.
* ALGORITHM:   none
* NOTES:       Use Ringbuf_Data_Peek with Ringbuf_Data_Put
*****************************************************************************/
bool Ringbuf_Data_Put(RING_BUFFER * b, volatile uint8_t *data_element)
{
    bool status = false;
    volatile uint8_t *ring_data = NULL; /* used to help point ring data */

    if (b)
		{
        /* limit the amount of elements that we accept */
        if (!Ringbuf_Full(b))
				{		//从当前写索引号读取数据块指针
            ring_data = b->buffer;
            ring_data += ((b->head % b->element_count) * b->element_size);
						//前一次Ringbuf_Data_Peek读取的当前写索引号的数据库已被pkt->buffer[0] = 55 FF .. .. .. ..覆盖
            if (ring_data == data_element)	
						{
                /* same chunk of memory - okay to signal the head */
                b->head++;	//写索引号++
                status = true;
            }
        }
    }
		
    return status;

/*data structure for MS/TP transmit packet
		
struct ring_buffer_t {
    volatile uint8_t *buffer;
    unsigned element_size;
    unsigned element_count;
    volatile unsigned head;
    volatile unsigned tail;
};
typedef struct ring_buffer_t RING_BUFFER;
static RING_BUFFER Transmit_Queue;

struct mstp_tx_packet {
		uint16_t length;
    uint16_t index;
    uint8_t buffer[MAX_MPDU];
};
static struct mstp_tx_packet *pkt;

初始化环形缓冲区 数据块buffer大小与pkt大小一致
Ringbuf_Init(&Transmit_Queue, (uint8_t *) & Transmit_Buffer, sizeof(struct mstp_tx_packet), MSTP_TRANSMIT_PACKET_COUNT);

pkt数据块的地址为环形缓冲区下一写入数据块地址， pkt->buffer[0] = 55 FF .. .. .. ..
pkt = (struct mstp_tx_packet *) Ringbuf_Data_Peek(&Transmit_Queue);	

将生成的pkt数据块放入环形缓冲区下一下一写入数据块地址的尾部
Ringbuf_Data_Put(&Transmit_Queue, (uint8_t *)pkt);	
*/

//data structure for MS/TP PDU Queue					PDU_Queue					PDU_Buffer	

}

/****************************************************************************
* DESCRIPTION: Configures the ring buffer
* RETURN:      none
* ALGORITHM:   none
* NOTES:
*   element_count must be a power of two
*****************************************************************************/
void Ringbuf_Init(
    RING_BUFFER * b,    				/* ring buffer structure */
    volatile uint8_t * buffer,  /* data block or array of data */
    unsigned element_size,      /* size of one element in the data block */
    unsigned element_count)     /* number of elements in the data block */
{
    if (b)
		{
        b->head = 0;											//写索引号=0
        b->tail = 0;											//读索引号=0
        b->buffer = buffer;								//缓冲区开始地址
        b->element_size = element_size;		//缓冲区数据块的大小
        b->element_count = element_count;	//缓冲区数据块的数量
    }

    return;
}

#ifdef TEST
#include <assert.h>
#include <string.h>
#include <limits.h>
#include "ctest.h"

/* test the ring buffer */
static void testRingAroundBuffer(
    Test * pTest,
    RING_BUFFER * test_buffer,
    uint8_t * data_element,
    unsigned element_size,
    unsigned element_count)
{
    volatile uint8_t *test_data;
    unsigned index;
    unsigned data_index;
    unsigned count;
    unsigned dummy;
    bool status;

    ct_test(pTest, Ringbuf_Empty(test_buffer));
    /* test the ring around the buffer */
    for (index = 0; index < element_count; index++) {
        for (count = 1; count < 4; count++) {
            dummy = index * count;
            for (data_index = 0; data_index < element_size; data_index++) {
                data_element[data_index] = dummy;
            }
            status = Ringbuf_Put(test_buffer, data_element);
            ct_test(pTest, status == true);
        }

        for (count = 1; count < 4; count++) {
            dummy = index * count;
            test_data = Ringbuf_Peek(test_buffer);
            ct_test(pTest, test_data);
            if (test_data) {
                for (data_index = 0; data_index < element_size; data_index++) {
                    ct_test(pTest, test_data[data_index] == dummy);
                }
            }
            (void) Ringbuf_Pop(test_buffer, NULL);
        }
    }
    ct_test(pTest, Ringbuf_Empty(test_buffer));
}

/* test the ring buffer */
static void testRingBuf(
    Test * pTest,
    uint8_t * data_store,
    uint8_t * data_element,
    unsigned element_size,
    unsigned element_count)
{
    RING_BUFFER test_buffer;
    volatile uint8_t *test_data;
    unsigned index;
    unsigned data_index;
    bool status;

    Ringbuf_Init(&test_buffer, data_store, element_size, element_count);
    ct_test(pTest, Ringbuf_Empty(&test_buffer));

    for (data_index = 0; data_index < element_size; data_index++) {
        data_element[data_index] = data_index;
    }
    status = Ringbuf_Put(&test_buffer, data_element);
    ct_test(pTest, status == true);
    ct_test(pTest, !Ringbuf_Empty(&test_buffer));

    test_data = Ringbuf_Peek(&test_buffer);
    for (data_index = 0; data_index < element_size; data_index++) {
        ct_test(pTest, test_data[data_index] == data_element[data_index]);
    }
    ct_test(pTest, !Ringbuf_Empty(&test_buffer));
    (void) Ringbuf_Pop(&test_buffer, NULL);
    ct_test(pTest, Ringbuf_Empty(&test_buffer));

    /* fill to max */
    for (index = 0; index < element_count; index++) {
        for (data_index = 0; data_index < element_size; data_index++) {
            data_element[data_index] = index;
        }
        status = Ringbuf_Put(&test_buffer, data_element);
        ct_test(pTest, status == true);
        ct_test(pTest, !Ringbuf_Empty(&test_buffer));
    }
    /* verify actions on full buffer */
    for (index = 0; index < element_count; index++) {
        for (data_index = 0; data_index < element_size; data_index++) {
            data_element[data_index] = index;
        }
        status = Ringbuf_Put(&test_buffer, data_element);
        ct_test(pTest, status == false);
        ct_test(pTest, !Ringbuf_Empty(&test_buffer));
    }

    /* check buffer full */
    for (index = 0; index < element_count; index++) {
        test_data = Ringbuf_Peek(&test_buffer);
        ct_test(pTest, test_data);
        if (test_data) {
            for (data_index = 0; data_index < element_size; data_index++) {
                ct_test(pTest, test_data[data_index] == index);
            }
        }
        (void) Ringbuf_Pop(&test_buffer, NULL);
    }
    ct_test(pTest, Ringbuf_Empty(&test_buffer));

    testRingAroundBuffer(pTest, &test_buffer, data_element, element_size,
        element_count);

    /* adjust the internal index of Ringbuf to test unsigned wrapping */
    test_buffer.head = UINT_MAX - 1;
    test_buffer.tail = UINT_MAX - 1;

    testRingAroundBuffer(pTest, &test_buffer, data_element, element_size,
        element_count);

    return;
}

void testRingBufSize16(
    Test * pTest)
{
    uint8_t data_element[5];
    uint8_t data_store[sizeof(data_element) * 16];

    testRingBuf(pTest, data_store, data_element, sizeof(data_element),
        sizeof(data_store) / sizeof(data_element));
}

void testRingBufSize32(
    Test * pTest)
{
    uint8_t data_element[16];
    uint8_t data_store[sizeof(data_element) * 32];

    testRingBuf(pTest, data_store, data_element, sizeof(data_element),
        sizeof(data_store) / sizeof(data_element));
}


#ifdef TEST_RING_BUFFER
int main(
    void)
{
    Test *pTest;
    bool rc;

    pTest = ct_create("Ring Buffer", NULL);

    /* individual tests */
    rc = ct_addTestFunction(pTest, testRingBufSize16);
    assert(rc);
    rc = ct_addTestFunction(pTest, testRingBufSize32);
    assert(rc);

    ct_setStream(pTest, stdout);
    ct_run(pTest);
    (void) ct_report(pTest);

    ct_destroy(pTest);

    return 0;
}
#endif
#endif