EtherCAT数据帧结构介绍

总报文

参照电子科技大学，蒲婉玲的学位论文“EtherCAT 主站与从站设计与实现”，Ether CAT 通信帧结构采用标准以外网帧结构，是通过对传统协议进行修改形成，在标准协议里插入专用帧类型的 Ether CAT 数据帧，也就是说，标准协议的数据内容就是 Ether CAT 的数据帧。专用帧类型用 0x88A4 进行标记。也因为如此，Ether CAT 通信可被标准的以太网通信完全兼容。
报文数据结构

子报文

子报文包含命令、索引、地址区长度、标志位、状态位、数据区和工作计数器等 7 个部分。报文中的命令一般是 8 位，用来表示报文寻址方式和读写操作；索引就是帧编码；从站通信地址是地址去中的 32 位二进制码；标志位 M 是后续报文的表示，如果 Ether CAT 数据帧有多个子报文，除最后一个子报文的标志位外，其他子报文的标志位都需要被职位；子报文数据属于用户自定义部分，长度一般是 1486 个 byte。

SOEM报文结构介绍

soem文件包中的ethercatmain.h文件中，定义了ecx_context报文数据帧结构和ec_slave子报文数据结构，下面将分别对其进行介绍。

总报文ecx_context

/** Context structure , referenced by all ecx functions*/
struct ecx_context
{/** port reference, may include red_port */ecx_portt      *port;/** slavelist reference */ec_slavet      *slavelist;/** number of slaves found in configuration */int            *slavecount;/** maximum number of slaves allowed in slavelist */int            maxslave;/** grouplist reference */ec_groupt      *grouplist;/** maximum number of groups allowed in grouplist */int            maxgroup;/** internal, reference to eeprom cache buffer */uint8          *esibuf;/** internal, reference to eeprom cache map */uint32         *esimap;/** internal, current slave for eeprom cache */uint16         esislave;/** internal, reference to error list */ec_eringt      *elist;/** internal, reference to processdata stack buffer info */ec_idxstackT   *idxstack;/** reference to ecaterror state */boolean        *ecaterror;/** reference to last DC time from slaves */int64          *DCtime;/** internal, SM buffer */ec_SMcommtypet *SMcommtype;/** internal, PDO assign list */ec_PDOassignt  *PDOassign;/** internal, PDO description list */ec_PDOdesct    *PDOdesc;/** internal, SM list from eeprom */ec_eepromSMt   *eepSM;/** internal, FMMU list from eeprom */ec_eepromFMMUt *eepFMMU;/** registered FoE hook */int            (*FOEhook)(uint16 slave, int packetnumber, int datasize);/** registered EoE hook */int            (*EOEhook)(ecx_contextt * context, uint16 slave, void * eoembx);/** flag to control legacy automatic state change or manual state change */int            manualstatechange;
};

需要特别注意

• 1 从站个数int *slavecount;
• 2 从站列表 ec_slavet *slavelist;

子报文ec_slave

/** for list of ethercat slaves detected */
typedef struct ec_slave
{/** state of slave */uint16           state;/** AL status code */uint16           ALstatuscode;/** Configured address */uint16           configadr;/** Alias address */uint16           aliasadr;/** Manufacturer from EEprom */uint32           eep_man;/** ID from EEprom */uint32           eep_id;/** revision from EEprom */uint32           eep_rev;/** Interface type */uint16           Itype;/** Device type */uint16           Dtype;/** output bits */uint16           Obits;/** output bytes, if Obits < 8 then Obytes = 0 */uint32           Obytes;/** output pointer in IOmap buffer */uint8            *outputs;/** startbit in first output byte */uint8            Ostartbit;/** input bits */uint16           Ibits;/** input bytes, if Ibits < 8 then Ibytes = 0 */uint32           Ibytes;/** input pointer in IOmap buffer */uint8            *inputs;/** startbit in first input byte */uint8            Istartbit;/** SM structure */ec_smt           SM[EC_MAXSM];/** SM type 0=unused 1=MbxWr 2=MbxRd 3=Outputs 4=Inputs */uint8            SMtype[EC_MAXSM];/** FMMU structure */ec_fmmut         FMMU[EC_MAXFMMU];/** FMMU0 function */uint8            FMMU0func;/** FMMU1 function */uint8            FMMU1func;/** FMMU2 function */uint8            FMMU2func;/** FMMU3 function */uint8            FMMU3func;/** length of write mailbox in bytes, if no mailbox then 0 */uint16           mbx_l;/** mailbox write offset */uint16           mbx_wo;/** length of read mailbox in bytes */uint16           mbx_rl;/** mailbox read offset */uint16           mbx_ro;/** mailbox supported protocols */uint16           mbx_proto;/** Counter value of mailbox link layer protocol 1..7 */uint8            mbx_cnt;/** has DC capability */boolean          hasdc;/** Physical type; Ebus, EtherNet combinations */uint8            ptype;/** topology: 1 to 3 links */uint8            topology;/** active ports bitmap : ....3210 , set if respective port is active **/uint8            activeports;/** consumed ports bitmap : ....3210, used for internal delay measurement **/uint8            consumedports;/** slave number for parent, 0=master */uint16           parent;/** port number on parent this slave is connected to **/uint8            parentport;/** port number on this slave the parent is connected to **/uint8            entryport;/** DC receivetimes on port A */int32            DCrtA;/** DC receivetimes on port B */int32            DCrtB;/** DC receivetimes on port C */int32            DCrtC;/** DC receivetimes on port D */int32            DCrtD;/** propagation delay */int32            pdelay;/** next DC slave */uint16           DCnext;/** previous DC slave */uint16           DCprevious;/** DC cycle time in ns */int32            DCcycle;/** DC shift from clock modulus boundary */int32            DCshift;/** DC sync activation, 0=off, 1=on */uint8            DCactive;/** link to config table */uint16           configindex;/** link to SII config */uint16           SIIindex;/** 1 = 8 bytes per read, 0 = 4 bytes per read */uint8            eep_8byte;/** 0 = eeprom to master , 1 = eeprom to PDI */uint8            eep_pdi;/** CoE details */uint8            CoEdetails;/** FoE details */uint8            FoEdetails;/** EoE details */uint8            EoEdetails;/** SoE details */uint8            SoEdetails;/** E-bus current */int16            Ebuscurrent;/** if >0 block use of LRW in processdata */uint8            blockLRW;/** group */uint8            group;/** first unused FMMU */uint8            FMMUunused;/** Boolean for tracking whether the slave is (not) responding, not used/set by the SOEM library */boolean          islost;/** registered configuration function PO->SO, (DEPRECATED)*/int              (*PO2SOconfig)(uint16 slave);/** registered configuration function PO->SO */int              (*PO2SOconfigx)(ecx_contextt * context, uint16 slave);/** readable name */char             name[EC_MAXNAME + 1];
} ec_slavet;

其中需要特别关注的是

• 1 从站id /** ID from EEprom */ uint32 eep_id;
• 2 输出指针/** output pointer in IOmap buffer */ uint8 *outputs;
• 3 输入指针/** input pointer in IOmap buffer */ uint8 *inputs;

ec_group数据结构

/** for list of ethercat slave groups */
typedef struct ec_group
{/** logical start address for this group */uint32           logstartaddr;/** output bytes, if Obits < 8 then Obytes = 0 */uint32           Obytes;/** output pointer in IOmap buffer */uint8            *outputs;/** input bytes, if Ibits < 8 then Ibytes = 0 */uint32           Ibytes;/** input pointer in IOmap buffer */uint8            *inputs;/** has DC capabillity */boolean          hasdc;/** next DC slave */uint16           DCnext;/** E-bus current */int16            Ebuscurrent;/** if >0 block use of LRW in processdata */uint8            blockLRW;/** IO segments used */uint16           nsegments;/** 1st input segment */uint16           Isegment;/** Offset in input segment */uint16           Ioffset;/** Expected workcounter outputs */uint16           outputsWKC;/** Expected workcounter inputs */uint16           inputsWKC;/** check slave states */boolean          docheckstate;/** IO segmentation list. Datagrams must not break SM in two. */uint32           IOsegment[EC_MAXIOSEGMENTS];
} ec_groupt;