一种802.15.4 CSMA-CA算法实现

ZigBee和6loWPAN都可使用802.15.4的MAC+PHY，802.15.4为了让节点更好地接入信道（channel），MAC层中使用了CSMA-CA机制。根据采用信标网络还是非信标网络，分别使用时隙CSMA-CA（适合星状网和树状网）和非时隙CSMA-CA(适合网状网)。

该实现方法尝试了非时隙CSMA-CA算法实现，时隙CSMA-CA将在日后进行补充。

使用方法：
1、初始化数据结构：
     tCsmaData.ucSlotted                  = CSMA_CA_WITHOUT_SLOTTED;  /* 非时隙 */
     tCsmaData.ucBatteryExtension = BATTERY_EXTENSION_DIS;          /* 不启用电池寿命扩展 */
     tCsmaData.pfCCA                      = CCA;                                                    /* 空闲信道评估函数（随机数模拟） */
     tCsmaData.pfRandom                = Random;                                              /*  随机数函数（ADC模拟） */
2、初始化CSMA-CA   CSMA_CA_Init(&tCsmaData);
3、使用CSMA-CA      ucReturn = CSMA_CA();
4、根据CSMA-CA 返回结果进行报文发送。

CSMA-CA.h

/******************************************************************************
* file   ：CSMA-CA.h
* Brief  ：Header file of 802.15.4 CSMA-CA algorithm - Ver. Beta
* Version：V0.10
* Author ：Ian
* Date ：2015年3月19日
* History：    Date            Editor    Version              Record
             2015-03-19      Ian          V0.10          Create, only CSMA-CA without
                                          time slots is realized.
******************************************************************************/
#ifndef _CSMA_CS_H_
#define _CSMA_CS_H_

#ifdef __cplusplus
extern "C" {
#endif

#define CSMA_CA_WITH_SLOTTED (1) /* CSMA-CA with time slott mode */
#define CSMA_CA_WITHOUT_SLOTTED (0) /* CSMA-CA with no time slott mode */
#define MAC_BE_MIN (3) /* Min. value of Backoff Exponent */
#define MAC_BE_MAX (5) /* Max. value of Backoff Exponent */
#define MAC_NB_MAX (4) /* Max. number of Backoff */
#define CHANNEL_BUSY (0) /* Indicate that channel is busy */
#define CHANNEL_CLR (1) /* Indicate that channel is clear */
#define BACKOFF_PERIOD_IN_US (20) /* Backoff time in us */
#define SW_OK (0) /* Successful operation */
#define SW_ERR (-1) /* Successful operation */
#define BATTERY_EXTENSION_EN (1) /* Battery life extension is enable */
#define BATTERY_EXTENSION_DIS (0) /* Battery life extension is disable*/


typedef unsigned char     CSMA_CA_MODE; /* Mode type of csma-ca */
typedef int RESULT; /* Result of function */

typedef struct _CSMA_CA_
{
    CSMA_CA_MODE  ucSlotted; /* CSAM-CA mode: Time slotted or non-slotted */
    uint8_t       ucBatteryExtension; /* Use batteryExtension or not */
    uint8_t (*pfCCA)(void); /* CCA performing function interface */
    uint8_t (*pfRandom)(void); /* Random function interface */
}T_CSMA_CA_DATA;

/*************************************************************************
* Function ：RESULT CSMA_CA_Init(T_CSMA_CA_DATA* ptCsma)
* Description ：Init CSMA-CA, Get & check necessary data struct
* Input Param ：T_CSMA_CA_DATA* ptCsma    Data struct for CSMA-CA
* Output Param：None
* Return      ：SW_ERR: Failed operation
                SW_OK : Successful operation
**************************************************************************/
RESULT CSMA_CA_Init(T_CSMA_CA_DATA* ptCsma);

/*************************************************************************
* Function ：RESULT CSMA_CA()
* Description ：Perform CSMA-CA, check a channel is available or not
* Input Param ：None
* Output Param：None
* Return      ：SW_ERR: Failed operation
                SW_OK : Successful operation
**************************************************************************/
RESULT CSMA_CA();

/*************************************************************************
* Function ：void CSMA_Backoff_Delay(uint8_t ucNum)
* Description ：Perform CSMA-CA Backoff
* Input Param ：uint8_t ucNum     Number of backoff period
* Output Param：None
* Return      ：None
**************************************************************************/
void CSMA_Backoff_Delay(uint8_t ucNum);

/*************************************************************************
* Function ：void Delay_ns(uint16_t ucNum)
* Description ：Wait for ucNum of backoff period
* Input Param ：uint8_t ucNum     Number of backoff period
* Output Param：None
* Return      ：None
**************************************************************************/
void Delay_ns(uint16_t ucNum);


#ifdef __cplusplus
}
#endif

#endif /* _CSMA_CA_H_ */

CSMA-CA.c

/******************************************************************************
* file   ：CSMA-CA.c
* Brief  ：802.15.4 CSMA-CA algorithm - Ver. Beta
* Version：V0.10
* Author ：Ian
* Date ：2015年3月19日
* History：     Date           Editor    Version    Record
            2015-03-19       Ian          V0.10           Create, only CSMA-CA without
                                           time slots is realized.
******************************************************************************/

#include "common.h"
#include "csma_ca.h"

static T_CSMA_CA_DATA *sg_ptCsma = {NULL}; /* Pointer for CSMA-CA data struct */

/*************************************************************************
* Function ：RESULT CSMA_CA_Init(T_CSMA_CA_DATA* ptCsma)
* Description ：Init CSMA-CA, Get & check necessary data struct
* Input Param ：T_CSMA_CA_DATA* ptCsma    Data struct for CSMA-CA
* Output Param：None
* Return      ：SW_ERR: Failed operation
                SW_OK : Successful operation
**************************************************************************/
RESULT CSMA_CA_Init(T_CSMA_CA_DATA* ptCsma)
{
    if ((NULL == ptCsma)\
      ||(NULL == ptCsma->pfCCA)\
      ||(NULL == ptCsma->pfRandom)) /* If the pointer is invalid, or if CCA/Random is not available */
    {
        return SW_ERR; /* return error */
    }

    sg_ptCsma = ptCsma; /* Get the data struct for the module */
    return SW_OK;
}

/*************************************************************************
* Function ：RESULT CSMA_CA()
* Description ：Perform CSMA-CA, check a channel is available or not
* Input Param ：None
* Output Param：None
* Return      ：SW_ERR: Failed operation
                SW_OK : Successful operation
**************************************************************************/
RESULT CSMA_CA()
{
    uint8_t ucBE,ucNB,ucRand,ucChClr;
    switch(sg_ptCsma->ucSlotted) /* Check if it is slotted mode of csma */
    {
        case CSMA_CA_WITH_SLOTTED: /* If it is slotted mode */
        {
            /* To be continued.. */
            break;

        }
        case CSMA_CA_WITHOUT_SLOTTED: /* If it is not slotted mode */
        {
            ucNB = 0; /* Set init value of NB */
            ucBE = MAC_BE_MIN; /* Set init value of BE */

            for (;ucNB <= MAC_NB_MAX;)/* If Number of backoff does not reach MAX.*/
            {
                ucRand = sg_ptCsma->pfRandom()%((1<<ucBE)-1); /* Get Random uint backoff delay */
                printf("Random value is %d , Max value is %d\n",ucRand, ((1<<ucBE) -1));
                CSMA_Backoff_Delay(ucRand); /* Delay random uint backoff period */
                ucChClr = sg_ptCsma->pfCCA(); /* Perform a CCA */

                if (CHANNEL_CLR == ucChClr) /* If the channel is clear */
                {
                    printf("CSMA-CA is ok!\n");
                    return SW_OK; /* Get the channel */
                }
                else /* If the channel is busy */
                {
                    ucNB++; /* Update NB value */
                    ucBE++; /* Update BE value */
                    ucBE = ((ucBE<MAC_BE_MAX)?ucBE : MAC_BE_MAX); /* Get the Min. value*/
                    printf("CSMA-CA is trying!, NB=%d, BE=%d\n",ucNB,ucBE);
                }
            }
            printf("CSMA-CA is failed!\n");
            return SW_ERR; /* Max number of backoff is over, fail to get clear channel */
            break;
        }
        default: /* Invalid mode */
        {
            break;
        }
    }
    return SW_ERR; /* failed operation */
}


/*************************************************************************
* Function ：void CSMA_Backoff_Delay(uint8_t ucNum)
* Description ：Perform CSMA-CA Backoff
* Input Param ：uint8_t ucNum     Number of backoff period
* Output Param：None
* Return      ：None
**************************************************************************/
void CSMA_Backoff_Delay(uint8_t ucNum)
{
    if(0 == ucNum)
    {
        return; /* if the number of backoff unit is 0, no delay is needed */
    }
    else
    {
        Delay_ns(ucNum*BACKOFF_PERIOD_IN_US);
    }
    return;
}

/*************************************************************************
* Function ：void Delay_ns(uint16_t ucNum)
* Description ：Wait for ucNum of backoff period
* Input Param ：uint8_t ucNum     Number of backoff period
* Output Param：None
* Return      ：None
**************************************************************************/
void Delay_ns(uint16_t ucNum)
{
    uint16_t wTemp;

    for (wTemp = 0; wTemp < ucNum; wTemp++)
    {
        ; /* Just wait */
    }
    return;
}

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