[lwip-users] Out Of Order Sequence (Segments?)

[Bill Auerbach]

Hello,

 

I want to understand Out Of Order Sequences (or is it segments?), why they result, and what lwIP does to limit them?  Can someone briefly tell me what it’s about, or point me to a good reference?  I find Google is spotty here for a good description except for a reference that it must be supported by a TCP/IP stack.

 

I ask because I’ve been chasing a system freeze (which is odd because the PowerPC is quite good about its exception handling).  It results from running out of PBUFs (RAW) in my Ethernet driver.  It turns out I am running out because of pbufs left on the ooseq list.  I didn’t know to account for pbufs for this use.  If I get to a state where pbuf_alloc returns NULL in my driver and I return NULL for what looks to be forever, the system freezes.  (The debugger won’t even break in which to date has been for a very bad thing J ).

 

Should there be a #define and a test and for the amount of ooseq’s to be allowed to be buffered?  If not, what is a practical limit?

 

What are the disadvantages of setting TCP_QUEUE_OOSEQ to 0?

 

If a driver doesn’t have pbufs and has to return NULL repeatedly, what should occur for it to recover these tied up pbufs?  I see that tcp_slow_tmr releases these ooseqs, but I seem to not get to this point.  Should returning NULL from low_level_input be a problem?

 

Thank you

Bill Auerbach