RE: [lwip-users] tcp_write() errors on snd_queuelen

[Tim Lambrix]

Andrew,
Thanks for your help too. I will take all I can get right now.  It looks like 
SYS_ARCH_PROTECT is defined as follows and it does hit this line of code (only 
from the interrupt itself however):
        sys_prot_t
        sys_arch_protect(void)
        {
                return((sys_prot_t)MAP_IntMasterDisable());
        }
I think this is correct?  However, the stellarisif_transmit function you 
mention is called in three places and only one of them has the SYS_ARCH_PROTECT 
called before it.  I don't see the calls in the interrupt itself 
stellarisif_interrupt.

Maybe I am missing something here but the problem I seem to have is the 
Ethernet interrupt goes off while I am in the tcp_write->tcp_enqueue function 
and changes the values of pcb->snd_queuelen. I have modified the local variable 
in that function queuelen to not use the value read at line 195 from:

        queuelen = pcb->snd_queuelen;    to
        queuelen = 0;

and line 411 from:

        pcb->snd_queuelen = queuelen;    to
        pcb->snd_queuelen += queuelen;

This fixes the issue but I welcome your insight on why it should not happen in 
the first place.  I don't see any calls close to SYS_ARCH_PROTECT in the 
tcp_write function to prevent the interrupt from going off.  I also tried 
disabling the Ethernet ISR for both ETH_INT_RX and ETH_INT_TX (the only two 
enabled) before calling tcp_write and enabling both after the call.  That also 
works to prevent the corruption of pcb-> snd_queuelen. 

>From what I have traced in code, the protection prevents the interrupt from 
>going off again while in the interrupt.  I have been trying to find where lwIP 
>gets processed outside of the interrupts if the interrupt is not suppose to 
>mess with the pbufs.  It looks to me like they can.

My original post of findings is here:
http://lists.nongnu.org/archive/html/lwip-users/2011-03/msg00069.html

Tim



-----Original Message-----
From: address@hidden [mailto:address@hidden On Behalf Of Andrew Foster
Sent: Wednesday, March 16, 2011 11:17 AM
To: Mailing list for lwIP users
Subject: Re: [lwip-users] tcp_write() errors on snd_queuelen

Tim,

Sorry for jumping in on this late in the thread. I've used the TI 
Port(1.3.2) a couple of times on different projects. Typically, I've 
used it in conjunction with FreeRTOS. One thing to be mindful of is 
making sure you have SYS_ARCH_PROTECT defined correctly.

stellarisif_output and stellarisif_transmit must be ran in critical 
sections with both the PBUF structure and the ETH TX FIFO protected. 
Otherwise, the stellarisif_interrupt can come in and modify the PBUF chain.

Again, I apologize if I'm stating the obvious here or things you've 
already ruled out. I wasn't able to find the original post.

Andrew
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