Re: [lwip-users] Using ARP to get MAC address

[Tomas D.]

On 2012.02.20 21:35, Kieran Mansley wrote:
> On 19 Feb 2012, at 13:42, Tomas D. wrote:
>
> > > If find_entry() is returning 0 (i.e. it has a row for that IP addr at index 0) 
> > > but etharp_find_addr() is returning -1 that must mean that the arp_table.state 
> > > for that row is not ETHARP_STATE_STABLE.  What is it?  That will show you the 
> > > problem.
> > Hello,
> > exactly, find_entry() returns 0 as index, but arp_table.state returns 
> > ETHARP_STATE_PENDING. I can't get it to go ETHARP_STATE_STABLE. Maybe someone 
> > could drop me some pointers how to solve this?
> Are you getting a valid ARP response from the other end?  It might be worth 
> tracing through what happens in lwIP when that packet is received to see why it 
> doesn't transition to STABLE as a result.
Hello again,
seems like my problem was solved temporarily :-)
The situation:
LwIP runs on a microcontroller, with no RTOS. The other microcontroller 
sends SPI command with remote IP address, so the first one with LwIP has 
to send ARP command and get the remote MAC.
I've implemented SPI interrupt, which receives the remote IP address and 
does ARP query. However my first tests were not inside an interrupt, so 
this code worked fine:
if(etharp_query() == ERR_OK) {
    while(etharp_find_addr() < 0) {
        ethernetif_input();
    }
}

Now if I try to do the same inside an interrupt, the controller hangs on 
the while() and I get no results and no exit from interrupt. Dead end. 
If I change the code to:
if(etharp_query() == ERR_OK) {
    if(etharp_find_addr() > -1) {
        //... do the stuff
    }
}
Then I get no answer after the first interrupt is done, but I get result 
when I send the same SPI command again and get into the second 
interrupt. This is logically explainable, since ethernetif_input() in 
the main cycle does the processing job. I don't understand why do I get 
while() hanged? Maybe someone could tell me how to solve this problem of 
getting IP address if I am inside interrupt where ethernetif_input() 
doesn't do the processing?

P.S. I've also tried:
if(etharp_query() == ERR_OK) {
    delay_ms(1000); // delay here one second
    ethernetif_input(); // process packet
    if(etharp_find_addr() > -1) {
        //... do the stuff
    }
}

But sometimes it works, sometimes not, but I also get processor hanged 
many times.

Thanks.

Tomas D.