FreakZ学习笔记：路由应答机制
路由应答机制是建立在路由发现和路由请求完成之后进行的，换句话说就是在通信链路建立完成之后，帧信息被传输到目的节点时，由目的节点进行的应答机制；路由应答机制在NWK.c下的mac_data_ind函数被调用，该函数的功能在另一篇文章《FreakZ学习笔记：接收过程详解》中有解释，这里不再赘述；相应代码如下：
switch (cmd.cmd_frm_id)
{
case NWK_CMD_RTE_REQ:
if(nib.dev_type != NWK_END_DEVICE)//Added by LiuTianmin
{
nwk_rte_mesh_rreq_handler(&hdr, &cmd);
}
break;
case NWK_CMD_RTE_REP:
if(nib.dev_type != NWK_END_DEVICE)//Added by LiuTianmin
{
nwk_rte_mesh_rrep_handler(&hdr, &cmd);
}
break;
case NWK_CMD_LEAVE:
nwk_leave_handler(&hdr, &cmd);
break;
default:
break;
}
这里的switch语句会分别对路由请求和路由应答的ID进行判断，如果节点类型为终端节点的话，即执行相应的路由请求函数nwk_rte_mesh_rreq_handler或路由应答函数nwk_rte_mesh_rrep_handler。
路由应答函数nwk_rte_mesh_rrep_handler的主要功能是处理传入的路由线路并确定是否需要路由应答；首先，需要确保本次路由应答有一个对应的发现表和路由表，如果没有，那么丢弃回复路线，同样，如果路径的成本比目前发现路由表里保存的链路成本高的话，同样放弃回复路线直到有一个更高效率的链路建立。如果这条路由应答是给当前链路的，那么结束路由发现过程并发送路由应答，否则，在前进的路由回复中更新记录路由请求的发现表。代码原型如下：
void nwk_rte_mesh_rrep_handler(const nwk_hdr_t *hdr_in, const nwk_cmd_t *cmd_in)
{
nwk_pcb_t *pcb = nwk_pcb_get();
nwk_nib_t *nib = nwk_nib_get();
mem_ptr_t *disc_mem_ptr;
mem_ptr_t *rte_mem_ptr;
U8 path_cost;
disc_mem_ptr = nwk_rte_disc_find(cmd_in->rrep.rreq_id, cmd_in->rrep.originator);
rte_mem_ptr = nwk_rte_tbl_find(cmd_in->rrep.responder);
path_cost = cmd_in->rrep.path_cost + NWK_STATIC_PATH_COST;
// if the rte entry or discovery entry doesn‘t exist or the path cost is not less than the current resid cost, then drop
// the rrep.
if ((!rte_mem_ptr) || (!disc_mem_ptr) || (path_cost >= DISC_ENTRY(disc_mem_ptr)->resid_cost))
{
if (!rte_mem_ptr || !disc_mem_ptr)
{///????????这里似乎有问题
nwk_rte_tbl_free(rte_mem_ptr);
nwk_rte_disc_free(disc_mem_ptr);
}
pcb->drop_rrep_frm++;
return;
}
// we‘ve met all the criteria to keep the rrep. that means we should update the rrep and disc entry.
// any time we update the next hop in the rte entry, we need to reset the discovery entry‘s expiry
DISC_ENTRY(disc_mem_ptr)->resid_cost = path_cost;
DISC_ENTRY(disc_mem_ptr)->expiry = NWK_RTE_DISC_TIME;
RTE_ENTRY(rte_mem_ptr)->next_hop = hdr_in->mac_hdr->src_addr.short_addr;
// update the entry to validation underway. once we send an actual frame through it, then we can change
// it to NWK_VALIDATION_UNDERWAY.
RTE_ENTRY(rte_mem_ptr)->status = (RTE_ENTRY(rte_mem_ptr)->status == NWK_DISCOVERY_UNDERWAY) ?
NWK_VALIDATION_UNDERWAY :
RTE_ENTRY(rte_mem_ptr)->status;
// check if the rrep is meant for us.
if (cmd_in->rrep.originator == nib->short_addr)
{
/*We should remove the roter request from req_list added by LiuTianmin*/
mem_ptr_t *mem_ptr;
mem_ptr = nwk_rte_mesh_rreq_find(nib->short_addr,cmd_in->rrep.responder);
nwk_rte_mesh_rreq_free(mem_ptr);
/*We should remove the roter request from req_list added by LiuTianmin*/
// send out pending xfers
nwk_pend_send_pending();
DBG_PRINT("\nNWK_RTE_MESH: Route established.\n");
return;
}
// forward the route reply
nwk_rte_mesh_send_rrep(cmd_in->rrep.rreq_id, cmd_in->rrep.originator, cmd_in->rrep.responder,
path_cost, DISC_ENTRY(disc_mem_ptr)->sender_addr);
}
nwk_rte_mesh_send_rrep为发送路由应答函数，原型如下：
static void nwk_rte_mesh_send_rrep(U8 rreq_id, U16 originator, U16 responder, U8 path_cost, U16 sender_addr)
{
nwk_nib_t *nib = nwk_nib_get();
nwk_hdr_t hdr;
nwk_cmd_t cmd;
buffer_t *buf;
cmd.cmd_frm_id = NWK_CMD_RTE_REP;
cmd.rrep.cmd_opts = 0x00;
cmd.rrep.rreq_id = rreq_id;
cmd.rrep.originator = originator;
cmd.rrep.responder = responder;
cmd.rrep.path_cost = path_cost;
hdr.nwk_frm_ctrl.frame_type = NWK_CMD_FRM;
hdr.nwk_frm_ctrl.disc_route = false;
hdr.src_addr = nib->short_addr;
hdr.dest_addr = sender_addr;
hdr.radius = (U8)(nib->max_depth << 1);
hdr.seq_num = nib->seq_num;
BUF_ALLOC(buf, TX);
nwk_gen_cmd(buf, &cmd);
debug_dump_nwk_cmd(&cmd);
//nwk_fwd(buf, &hdr); //Delete by LiuTianmin
/*I think here should respone direct to the sender*/
mac_hdr_t mac_hdr_out;
buf->len = aMaxPHYPacketSize - (buf->dptr - buf->buf);
hdr.mac_hdr = &mac_hdr_out;
hdr.mac_hdr->src_addr.mode = SHORT_ADDR;
hdr.mac_hdr->dest_addr.mode = SHORT_ADDR;
hdr.mac_hdr->src_addr.short_addr = nib->short_addr;
hdr.mac_hdr->dest_addr.short_addr = hdr.dest_addr;
nwk_tx(buf, &hdr, false);
}
当路由应答产生之后，会通过nwk_tx函数将该路由应答由NWK层传递到MAC层，通过MAC层到达Radio层，然后将应答信息发送。