"Robert Schilling" <[email protected]> wrote:
I'm trying to port port lwIP to a ARM Cortex M3 NXP LPC1768.
I'm using following Example:
http://www.coocox.com/EXAMPLE/NXP_LPC1766_ARMCC.htm
If I want to ping the device, ARP requests of the host computer are coming
in, but the device doesn't reply them.
I could isolate the problem to the function update_arp_entry() where the
reply should be started.
There is a loop, where the queued packets should be sent: while
(arp_table[i].q != NULL).
In my case arp_table[0] gets initialized but arp_table[0].q is always
NULL.
For this reason I don't get an ARP reply.
Hi Robert
You misunderstand the purpose of that queue.
arp_table[i].q is used to hold outgoing IP packets which have not yet been
sent because LWIP didn't know the MAC address of the destination device. In
this situation, LWIP issues an ARP request while queueing the outgoing IP
packet, and when the ARP reply arrives from the other device, pending
packets can be sent. In your case there is nothing on that queue because
LWIP hasn't tried to send any IP packets yet.
Your problem is the opposite way around: the other device is sending an ARP
request, and LWIP is not sending the ARP reply.
When an ARP request is received, LWIP calls update_arp_entry() as a side
effect: the incoming ARP request provides enough information for LWIP to
update an entry in its own (outgoing) address table, saving LWIP from having
to issue its own ARP request if it needs to send something to the IP address
of the other device.
This call to update_arp_entry() is from etharp_arp_input(). The code to send
the ARP reply is a little further down that function. Find "case
ARP_REQUEST". The code there construct an ARP reply and calls
netif->linkoutput() to send it. You should trace through that code and work
out why the transmission is not occurring.
The most likely explanation is that for some reason your Ethernet driver is
unable to transmit anything.
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