Hi Frank, LwIP can manage checksums either through software or by offloading the task to hardware.
You can configure these options in `lwipopt.h`: ```c //*************************************************** // ---------- checksum options ---------- //*************************************************** //#define CHECKSUM_GEN_IP 1 //#define CHECKSUM_GEN_UDP 1 //#define CHECKSUM_GEN_TCP 1 //#define CHECKSUM_CHECK_IP 1 //#define CHECKSUM_CHECK_UDP 1 //#define CHECKSUM_CHECK_TCP 1 ``` Regards, Rémy Le sam. 12 avr. 2025 à 08:04, Nathan Martin <t...@t2n.org> a écrit : > lwIP does not generate the Ethernet frame check sequence (FCS) value on > packet output. That responsbility is on the Ethernet / Wi-Fi driver or > hardware MAC. lwIP also does not check the Ethernet FCS value on packet > input processing either. Both cases are so commonly handled by MAC+PHY > hardware side its probably why it wasn't implemented in LwIP. > > However I can confirm that the UDP checksum is being generated > successfully in your packet dump: > > 000028 *59 A9* 01 01 06 00 01 00 > > > May I ask what MAC+PHY you're using? > > > -Nathan > > > On 4/11/2025 6:38 PM, Van Hooft, Frank via lwip-users wrote: > > I have a single ethernet netif and have it configured (I believe) to > calculate & generate checksums. This is in a no-OS environment. I am > trying to use DHCP. But packets generated by LwIP always have zeros at the > end. > > Here's what I see, from a start-up, with some logging enabled: > > > netif: added interface A0 IP addr 0.0.0.0 netmask 0.0.0.0 gw 0.0.0.0 > netif: setting default interface A0 > dhcp_start(netif=0x200001a0) A00 > dhcp_start(): mallocing new DHCP client > dhcp_start(): allocated dhcp > dhcp_start(): starting DHCP configuration > udp_bind(ipaddr = 0.0.0.0, port = 68) > udp_bind: bound to 0.0.0.0, port 68) > udp_connect: connected to 0.0.0.0, port 67) > dhcp_discover() > transaction id xid(abcd0001) > dhcp_discover: making request > dhcp_discover: sendto(DISCOVER, IP_ADDR_BROADCAST, > LWIP_IANA_PORT_DHCP_SERVER) > udp_send: added header in given pbuf 0x20003124 > udp_send: sending datagram of length 316 > udp_send: UDP packet length 316 > udp_send: UDP checksum 0xa959 > udp_send: ip_output_if (,,,,0x11,) > ethernet_output: sending packet 0x20003124 > > > 000000 FF FF FF FF FF FF 38 24 > 000008 31 06 C6 C3 00 08 45 00 > 000010 50 01 00 00 00 00 FF 11 > 000018 6B EC 00 00 00 00 FF FF > 000020 FF FF 44 00 43 00 3C 01 > 000028 59 A9 01 01 06 00 01 00 > 000030 CD AB 00 00 00 00 00 00 > 000038 00 00 00 00 00 00 00 00 > 000040 00 00 00 00 00 00 38 24 > 000048 31 06 C6 C3 00 00 00 00 > 000050 00 00 00 00 00 00 00 00 > 000058 00 00 00 00 00 00 00 00 > 000060 00 00 00 00 00 00 00 00 > 000068 00 00 00 00 00 00 00 00 > 000070 00 00 00 00 00 00 00 00 > 000078 00 00 00 00 00 00 00 00 > 000080 00 00 00 00 00 00 00 00 > 000088 00 00 00 00 00 00 00 00 > 000090 00 00 00 00 00 00 00 00 > 000098 00 00 00 00 00 00 00 00 > 0000A0 00 00 00 00 00 00 00 00 > 0000A8 00 00 00 00 00 00 00 00 > 0000B0 00 00 00 00 00 00 00 00 > 0000B8 00 00 00 00 00 00 00 00 > 0000C0 00 00 00 00 00 00 00 00 > 0000C8 00 00 00 00 00 00 00 00 > 0000D0 00 00 00 00 00 00 00 00 > 0000D8 00 00 00 00 00 00 00 00 > 0000E0 00 00 00 00 00 00 00 00 > 0000E8 00 00 00 00 00 00 00 00 > 0000F0 00 00 00 00 00 00 00 00 > 0000F8 00 00 00 00 00 00 00 00 > 000100 00 00 00 00 00 00 00 00 > 000108 00 00 00 00 00 00 00 00 > 000110 00 00 00 00 00 00 63 53 > 000118 82 63 35 01 01 39 02 05 > 000120 DC 0C 08 53 50 45 5F 54 > 000128 65 73 74 37 03 01 03 1C > 000130 FF 00 00 00 00 00 00 00 > 000138 00 00 00 00 00 00 00 00 > 000140 00 00 00 00 00 00 00 00 > 000148 00 00 00 00 00 00 00 00 > 000150 00 00 00 00 00 00 00 00 > 000158 00 00 00 00 00 00 > > > dhcp_discover: deleting() > dhcp_discover: SELECTING > dhcp_discover(): set request timeout 2000 msecs > > NETIF > MTU=0x5DC > CkhSum Flgs=0xFFFF > Flags=0x3F > IP=0x0 > NetMask=0x0 > GW=0x0 > > > The packet printout and some netif contents printout is debugging I've > added. This packet is transmitted, as-is, onto the line. Wireshark sees > this packet (unchanged as above), and wireshark complains about the invalid > FCS. > > I am new to LwIP, so I assume I'm doing something wrong in my setup. > > I'm assuming the above is a DHCP discover packet? > > Any idea how to get the FCS working at the end of the packet? > > > > My lwipopts.h file contents looks like this: > > > #define PROCESSOR_LITTLE_ENDIAN > > #define LWIP_DEBUG 1 > #define ETHARP_DEBUG LWIP_DBG_ON > #define NETIF_DEBUG LWIP_DBG_ON > #define DHCP_DEBUG LWIP_DBG_ON > #define UDP_DEBUG LWIP_DBG_ON > #define MEMP_DEBUG LWIP_DBG_ON > #define MEM_DEBUG LWIP_DBG_ON > //#define ICMP_DEBUG LWIP_DBG_ON > > #define NO_SYS 1 > #define MEM_LIBC_MALLOC 0 > #define MEM_CUSTOM_ALLOCATOR 0 > #define MEMP_MEM_INIT 1 > #define MEM_ALIGNMENT 4 > #define MEM_SIZE 1600 > > #define MEM_USE_POOLS 1 > #define MEM_USE_POOLS_TRY_BIGGER_POOL 1 > #define MEMP_USE_CUSTOM_POOLS 1 > > #define LWIP_IPV4 1 > #define LWIP_IPV6 0 > #define LWIP_UDP 1 > #define LWIP_TCP 0 > #define LWIP_ARP 1 > #define LWIP_ICMP 1 > #define LWIP_DHCP 1 > #define LWIP_AUTOIP 0 > // LWIP_ARP enables LWIP_ETHERNET in opt.h > > #define IP_REASSEMBLY 0 > #define IP_FRAG 0 > > #define LWIP_RAW 1 > #define LWIP_NETCONN 0 > #define LWIP_SOCKET 0 > > #define LWIP_NETIF_TX_SINGLE_PBUF 1 > #define LWIP_SINGLE_NETIF 1 > > // This defaults to 0, but it can be nice to > // have a hostname, for human readability > #define LWIP_NETIF_HOSTNAME 1 > > #define LWIP_CHECKSUM_CTRL_PER_NETIF 1 > #define CHECKSUM_GEN_IP 1 > #define CHECKSUM_GEN_UDP 1 > #define CHECKSUM_GEN_TCP 1 > #define CHECKSUM_GEN_ICMP 1 > #define CHECKSUM_GEN_ICMP6 1 > #define CHECKSUM_CHECK_IP 1 > #define CHECKSUM_CHECK_UDP 1 > #define CHECKSUM_CHECK_TCP 1 > #define CHECKSUM_CHECK_ICMP 1 > #define CHECKSUM_CHECK_ICMP6 1 > #define LWIP_CHECKSUM_ON_COPY 0 > > > > Many thanks. > > *Frank* > > _______________________________________________ > lwip-users mailing > listlwip-users@nongnu.orghttps://lists.nongnu.org/mailman/listinfo/lwip-users > > > _______________________________________________ > lwip-users mailing list > lwip-users@nongnu.org > https://lists.nongnu.org/mailman/listinfo/lwip-users >
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