本篇是從0學(xué)ARM系列文章的最后一篇，后面暫無(wú)更新計(jì)劃。
想學(xué)習(xí)ARM知識(shí)，建議收藏下面的合集的鏈接。
《從0學(xué)ARM》
網(wǎng)卡的驅(qū)動(dòng)，對(duì)于上層協(xié)議來(lái)說(shuō)，已經(jīng)封裝好了發(fā)送和接收數(shù)據(jù)的接口，那么上層協(xié)議棧只需要按照順序調(diào)用對(duì)應(yīng)的網(wǎng)卡驅(qū)動(dòng)函數(shù)就可以進(jìn)行網(wǎng)絡(luò)數(shù)據(jù)的收發(fā)。
uboot中的協(xié)議棧相對(duì)來(lái)說(shuō)比較簡(jiǎn)單，有以下幾個(gè)特點(diǎn)：
下面是uboot網(wǎng)絡(luò)協(xié)議棧的函數(shù)調(diào)用流程：
uboot中，所有的命令都用宏U_BOOT_CMD來(lái)定義， dns命令的定義如下：
426 U_BOOT_CMD(
427 dns, 3, 1, do_dns,
428 "lookup the IP of a hostname",
429 "hostname [envvar]"
430 );
當(dāng)我們?cè)趗boot的命令終端輸入命令dns后，命令解析函數(shù)就會(huì)調(diào)用dns執(zhí)行函數(shù)do_dns()
389 int do_dns(cmd_tbl_t *cmdtp, int flag, int argc, char * const argv[])
390 {
……
406 if (strlen(argv[1]) >= 255) {
407 printf("dns error: hostname too long\n");
408 return 1;
409 }
410
411 NetDNSResolve = argv[1];
412
413 if (argc == 3)
414 NetDNSenvvar = argv[2];
415 else
416 NetDNSenvvar = NULL;
417
418 if (NetLoop(DNS) < 0) {
419 printf("dns lookup of %s failed, check setup\n", argv[1]);
420 return 1;
421 }
422
423 return 0;
424 }
406行 判斷參數(shù)字符串長(zhǎng)度，大于255非法 411行 參數(shù)1必須是要解析的主機(jī)，存儲(chǔ)在NetDNSResolve 中 413~416行 保存dns命令的環(huán)境參數(shù)，該參數(shù)可以沒(méi)有 418行 進(jìn)入網(wǎng)絡(luò)協(xié)議處理函數(shù)入口NetLoop()，并將對(duì)應(yīng)的協(xié)議DNS傳遞給該函數(shù)
NetLoop()代碼比較長(zhǎng)，我們只分析其中比較重要的幾段代碼
316 /**********************************************************************/
317 /*
318 * Main network processing loop.
319 */
320
321 int NetLoop(enum proto_t protocol)
322 {
323 bd_t *bd = gd->bd;
324 int ret = -1;
…………
352 NetInitLoop();
…………
367 switch (protocol) {
368 case TFTPGET:
369 #ifdef CONFIG_CMD_TFTPPUT
370 case TFTPPUT:
371 #endif
372 /* always use ARP to get server ethernet address */
373 TftpStart(protocol);
374 break;
…………
426 #if defined(CONFIG_CMD_DNS)
427 case DNS:
428 DnsStart();
429 break;
430 #endif
438 }
…………
461 for (;;) {
462 WATCHDOG_RESET();
463 #ifdef CONFIG_SHOW_ACTIVITY
464 show_activity(1);
465 #endif
466 /*
467 * Check the ethernet for a new packet. The ethernet
468 * receive routine will process it.
469 */
470 eth_rx();
471
472 /*
473 * Abort if ctrl-c was pressed.
474 */
475 if (ctrlc()) {
476 /* cancel any ARP that may not have completed */
477 NetArpWaitPacketIP = 0;
478
479 net_cleanup_loop();
480 eth_halt();
481 /* Invalidate the last protocol */
482 eth_set_last_protocol(BOOTP);
483
484 puts("\nAbort\n");
485 /* include a debug print as well incase the debug
486 messages are directed to stderr */
487 debug_cond(DEBUG_INT_STATE, "--- NetLoop Abort!\n");
488 goto done;
489 }
…………
522 switch (net_state) {
523
524 case NETLOOP_RESTART:
525 NetRestarted = 1;
526 goto restart;
527
528 case NETLOOP_SUCCESS:
529 net_cleanup_loop();
530 if (NetBootFileXferSize > 0) {
531 char buf[20];
532 printf("Bytes transferred = %ld (%lx hex)\n",
533 NetBootFileXferSize,
534 NetBootFileXferSize);
535 sprintf(buf, "%lX", NetBootFileXferSize);
536 setenv("filesize", buf);
537
538 sprintf(buf, "%lX", (unsigned long)load_addr);
539 setenv("fileaddr", buf);
540 }
541 if (protocol != NETCONS)
542 eth_halt();
543 else
544 eth_halt_state_only();
545
546 eth_set_last_protocol(protocol);
547
548 ret = NetBootFileXferSize;
549 debug_cond(DEBUG_INT_STATE, "--- NetLoop Success!\n");
550 goto done;
551
552 case NETLOOP_FAIL:
553 net_cleanup_loop();
554 /* Invalidate the last protocol */
555 eth_set_last_protocol(BOOTP);
556 debug_cond(DEBUG_INT_STATE, "--- NetLoop Fail!\n");
557 goto done;
558
559 case NETLOOP_CONTINUE:
560 continue;
561 }
562 }
563
564 done:
565 #ifdef CONFIG_CMD_TFTPPUT
566 /* Clear out the handlers */
567 net_set_udp_handler(NULL);
568 net_set_icmp_handler(NULL);
569 #endif
570 return ret;
571 }
函數(shù)參數(shù)為DNS 352行 初始化網(wǎng)絡(luò)信息,讀取ipaddr、gatewayip、netmask、serverip、dnsip等環(huán)境變量的值并復(fù)制到對(duì)應(yīng)的全局變量中
static void NetInitLoop(void)
{
static int env_changed_id;
int env_id = get_env_id();
/* update only when the environment has changed */
if (env_changed_id != env_id) {
NetOurIP = getenv_IPaddr("ipaddr");
NetOurGatewayIP = getenv_IPaddr("gatewayip");
NetOurSubnetMask = getenv_IPaddr("netmask");
NetServerIP = getenv_IPaddr("serverip");
NetOurNativeVLAN = getenv_VLAN("nvlan");
NetOurVLAN = getenv_VLAN("vlan");
#if defined(CONFIG_CMD_DNS)
NetOurDNSIP = getenv_IPaddr("dnsip");
#endif
env_changed_id = env_id;
}
memcpy(NetOurEther, eth_get_dev()->enetaddr, 6);
return;
}
367行 對(duì)傳入的參數(shù)做switch操作，不同的協(xié)議進(jìn)入到不同的處理流程 428行 執(zhí)行DnsStart(),
197 void
198 DnsStart(void)
199 {
200 debug("%s\n", __func__);
201
202 NetSetTimeout(DNS_TIMEOUT, DnsTimeout);
203 net_set_udp_handler(DnsHandler);
204
205 DnsSend();
206 }
203行 函數(shù)net_set_udp_handler()主要將dns協(xié)議的回調(diào)函數(shù)DnsHandler()注冊(cè)到udp協(xié)議的回調(diào)指針udp_packet_handler，
void net_set_udp_handler(rxhand_f *f)
{
debug_cond(DEBUG_INT_STATE, "--- NetLoop UDP handler set (%p)\n", f);
if (f == NULL)
udp_packet_handler = dummy_handler;//注冊(cè)到udp協(xié)議回調(diào)函數(shù)指針
else
udp_packet_handler = f;
}
DnsStart()最終會(huì)調(diào)用函數(shù)DnsSend()發(fā)送dns協(xié)議數(shù)據(jù)包，該函數(shù)是根據(jù)dns協(xié)議填充udp數(shù)據(jù)包
37 static void
38 DnsSend(void)
39 {
40 struct header *header;
41 int n, name_len;
42 uchar *p, *pkt;
43 const char *s;
44 const char *name;
45 enum dns_query_type qtype = DNS_A_RECORD;
46
47 name = NetDNSResolve;
48 pkt = p = (uchar *)(NetTxPacket + NetEthHdrSize() + IP_UDP_HDR_SIZE);
49
50 /* Prepare DNS packet header */
51 header = (struct header *) pkt;
52 header->tid = 1;
53 header->flags = htons(0x100); /* standard query */
54 header->nqueries = htons(1); /* Just one query */
55 header->nanswers = 0;
56 header->nauth = 0;
57 header->nother = 0;
58
59 /* Encode DNS name */
60 name_len = strlen(name);
61 p = (uchar *) &header->data; /* For encoding host name into packet */
62
63 do {
64 s = strchr(name, '.');
65 if (!s)
66 s = name + name_len;
67
68 n = s - name; /* Chunk length */
69 *p++ = n; /* Copy length */
70 memcpy(p, name, n); /* Copy chunk */
71 p += n;
72
73 if (*s == '.')
74 n++;
75
76 name += n;
77 name_len -= n;
78 } while (*s != '\0');
79
80 *p++ = 0; /* Mark end of host name */
81 *p++ = 0; /* Some servers require double null */
82 *p++ = (unsigned char) qtype; /* Query Type */
83
84 *p++ = 0;
85 *p++ = 1; /* Class: inet, 0x0001 */
86
87 n = p - pkt; /* Total packet length */
88 debug("Packet size %d\n", n);
89
90 DnsOurPort = random_port();
91
92 NetSendUDPPacket(NetServerEther, NetOurDNSIP, DNS_SERVICE_PORT,
93 DnsOurPort, n);
94 debug("DNS packet sent\n");
95 }
51~57行 根據(jù)dns協(xié)議填充dns協(xié)議頭，數(shù)據(jù)幀首地址為NetTxPacket，此處通過(guò)指針pkt和p來(lái)填充dns數(shù)據(jù)幀 60~85行 根據(jù)協(xié)議格式要求填充要解析的host名字到數(shù)據(jù)包 87行 計(jì)算數(shù)據(jù)包長(zhǎng)度 90行 產(chǎn)生一個(gè)隨機(jī)的端口號(hào) 92~93行 調(diào)用udp協(xié)議的發(fā)送函數(shù)NetSendUDPPacket(),參數(shù)依次是：以太頭信息，DNS服務(wù)器 ip地址，DNS服務(wù)器端口號(hào)，我們的dns服務(wù)端口號(hào)，數(shù)據(jù)包長(zhǎng)度
688 int NetSendUDPPacket(uchar *ether, IPaddr_t dest, int dport, int sport,
689 int payload_len)
690 {
691 uchar *pkt;
692 int eth_hdr_size;
693 int pkt_hdr_size;
694
695 /* make sure the NetTxPacket is initialized (NetInit() was called) */
696 assert(NetTxPacket != NULL);
697 if (NetTxPacket == NULL)
698 return -1;
699
700 /* convert to new style broadcast */
701 if (dest == 0)
702 dest = 0xFFFFFFFF;
703
704 /* if broadcast, make the ether address a broadcast and don't do ARP */
705 if (dest == 0xFFFFFFFF)
706 ether = NetBcastAddr;
707
708 pkt = (uchar *)NetTxPacket;
709
710 eth_hdr_size = NetSetEther(pkt, ether, PROT_IP);
711 pkt += eth_hdr_size;
712 net_set_udp_header(pkt, dest, dport, sport, payload_len);
713 pkt_hdr_size = eth_hdr_size + IP_UDP_HDR_SIZE;
714
715 /* if MAC address was not discovered yet, do an ARP request */
716 if (memcmp(ether, NetEtherNullAddr, 6) == 0) {
717 debug_cond(DEBUG_DEV_PKT, "sending ARP for %pI4\n", &dest);
718
719 /* save the ip and eth addr for the packet to send after arp */
720 NetArpWaitPacketIP = dest;
721 NetArpWaitPacketMAC = ether;
722
723 /* size of the waiting packet */
724 NetArpWaitTxPacketSize = pkt_hdr_size + payload_len;
725
726 /* and do the ARP request */
727 NetArpWaitTry = 1;
728 NetArpWaitTimerStart = get_timer(0);
729 ArpRequest();
730 return 1; /* waiting */
731 } else {
732 debug_cond(DEBUG_DEV_PKT, "sending UDP to %pI4/%pM\n",
733 &dest, ether);
734 NetSendPacket(NetTxPacket, pkt_hdr_size + payload_len);
735 return 0; /* transmitted */
736 }
737 }
696~706行 參數(shù)檢查 710行 設(shè)置以太頭 713行 設(shè)置udp協(xié)議頭 716~730行 如果沒(méi)有目的MAC地址，就要先發(fā)送ARP請(qǐng)求 734行 調(diào)用函數(shù)NetSendPacket()，參數(shù)分別是：要發(fā)送數(shù)據(jù)幀的首地址，數(shù)據(jù)包長(zhǎng)度
529 /* Transmit a packet */
530 static inline void NetSendPacket(uchar *pkt, int len)
531 {
532 (void) eth_send(pkt, len);
533 }
532行 調(diào)用我們注冊(cè)的函數(shù)dm9000_send() 該函數(shù)已經(jīng)分析過(guò)，根據(jù)流程圖，回到函數(shù)NetLoop()
461~562行 循環(huán)接收網(wǎng)絡(luò)數(shù)據(jù)包 470行 調(diào)用網(wǎng)卡驅(qū)動(dòng)接收函數(shù)eth_rx()
int eth_rx(void)
{
if (!eth_current)
return -1;
return eth_current->recv(eth_current);
}
eth_current->recv(eth_current)函數(shù)就是我們注冊(cè)的網(wǎng)卡的接收函數(shù)dm9000_rx()，該函數(shù)我們上一章已經(jīng)分析過(guò)，最終通過(guò)調(diào)用函數(shù)NetReceive()，將數(shù)據(jù)幀上傳到協(xié)議棧
943 void
944 NetReceive(uchar *inpkt, int len)
945 {
946 struct ethernet_hdr *et;
947 struct ip_udp_hdr *ip;
948 IPaddr_t dst_ip;
949 IPaddr_t src_ip;
950 int eth_proto;
……
957
958 NetRxPacket = inpkt;
959 NetRxPacketLen = len;
960 et = (struct ethernet_hdr *)inpkt;
961
962 /* too small packet? */
963 if (len < ETHER_HDR_SIZE)
964 return;
965
……
984
985 eth_proto = ntohs(et->et_protlen);
986
987 if (eth_proto < 1514) {
988 struct e802_hdr *et802 = (struct e802_hdr *)et;
……
997
998 } else if (eth_proto != PROT_VLAN) { /* normal packet */
999 ip = (struct ip_udp_hdr *)(inpkt + ETHER_HDR_SIZE);
1000 len -= ETHER_HDR_SIZE;
1001
1002 } else { /* VLAN packet */
……
1026 }
1027
……
1045 switch (eth_proto) {
……
1056 case PROT_IP:
1057 debug_cond(DEBUG_NET_PKT, "Got IP\n");
1058 /* Before we start poking the header, make sure it is there */
1059 if (len < IP_UDP_HDR_SIZE) {
1060 debug("len bad %d < %lu\n", len,
1061 (ulong)IP_UDP_HDR_SIZE);
1062 return;
1063 }
1064 /* Check the packet length */
1065 if (len < ntohs(ip->ip_len)) {
1066 debug("len bad %d < %d\n", len, ntohs(ip->ip_len));
1067 return;
1068 }
1069 len = ntohs(ip->ip_len);
1070 debug_cond(DEBUG_NET_PKT, "len=%d, v=%02x\n",
1071 len, ip->ip_hl_v & 0xff);
1072
1073 /* Can't deal with anything except IPv4 */
1074 if ((ip->ip_hl_v & 0xf0) != 0x40)
1075 return;
1076 /* Can't deal with IP options (headers != 20 bytes) */
1077 if ((ip->ip_hl_v & 0x0f) > 0x05)
1078 return;
1079 /* Check the Checksum of the header */
1080 if (!NetCksumOk((uchar *)ip, IP_HDR_SIZE / 2)) {
1081 debug("checksum bad\n");
1082 return;
1083 }
1084 /* If it is not for us, ignore it */
1085 dst_ip = NetReadIP(&ip->ip_dst);
1092 /* Read source IP address for later use */
1093 src_ip = NetReadIP(&ip->ip_src);
1184 /*
1185 * IP header OK. Pass the packet to the current handler.
1186 */
1187 (*udp_packet_handler)((uchar *)ip + IP_UDP_HDR_SIZE,
1188 ntohs(ip->udp_dst),
1189 src_ip,
1190 ntohs(ip->udp_src),
1191 ntohs(ip->udp_len) - UDP_HDR_SIZE);
1192 break;
1193 }
1194 }
參數(shù)inpkt：指向接收到的以太數(shù)據(jù)包頭 len：接收到的數(shù)據(jù)包的長(zhǎng)度 960行 變量NetRxPacket指向接收的數(shù)據(jù)頭，以太數(shù)據(jù)包包頭比定位以太協(xié)議頭 985行 從以太協(xié)議頭提取出協(xié)議字段，該字段表示后面是否是ip協(xié)議 999行 解析出ip協(xié)議頭 1045行 根據(jù)以太頭協(xié)議進(jìn)行switch操作 1059~1083行 對(duì)協(xié)議頭進(jìn)行合法性檢查 1085行 讀取出目的ip地址 1093行 讀取出源ip地址， 1187行 ip協(xié)議頭解析成功，調(diào)用udp協(xié)議回調(diào)函數(shù)udp_packet_handler(),該函數(shù)在之前的DnStart()注冊(cè)了DnsHandler
104 static void
105 DnsHandler(uchar *pkt, unsigned dest, IPaddr_t sip, unsigned src, unsigned len)
106 {
193
194 net_set_state(NETLOOP_SUCCESS);
195 }
該函數(shù)用于解析DNS協(xié)議，在此不再詳解 解析成功后194行，會(huì)設(shè)置當(dāng)前執(zhí)行狀態(tài)為NETLOOP_SUCCESS， 代碼回到函數(shù)NetLoop()470行 475行 判斷是否按下ctrl+c快捷鍵，并作出操作 522~562行 對(duì)執(zhí)行結(jié)果進(jìn)行處理，計(jì)入統(tǒng)計(jì)信息 564行 如果net_state為NETLOOP_SUCCESS、NETLOOP_FAIL最終都會(huì)進(jìn)入done，從而置空udp回調(diào)函數(shù) 如果net_state為NETLOOP_CONTINUE，表明仍然有后續(xù)數(shù)據(jù)包要接收，則回到461行，繼續(xù)下一個(gè)數(shù)據(jù)包的接收
至此DNS協(xié)議的處理流程分析完畢，大家可以根據(jù)這個(gè)流程自行分析其他幾個(gè)協(xié)議的處理流程。
有的時(shí)候能讀取到 DM9000A 的 ID，連續(xù)操作就能讀取到 DM9000A 的 ID，但間隔一會(huì)操作就讀取不到 DM9000A 的 ID，通過(guò)調(diào)試，在 dm9000_reset 函數(shù)中加一句延時(shí)操作，就可以正常讀取 DM9000A 的 ID 了。
277 do {
278 DM9000_DBG("resetting the DM9000, 2nd reset\n");
279 udelay(25); /* Wait at least 20 us */
280 } while (DM9000_ior(DM9000_NCR) & 1);
281 udelay(150);
282 /* Check whether the ethernet controller is present */
283 if ((DM9000_ior(DM9000_PIDL) != 0x0) ||
284 (DM9000_ior(DM9000_PIDH) != 0x90))
285 printf("ERROR: resetting DM9000 -> not responding\n");
