There isn't much out there that describes these settings in good detail. However, TCP_MSS is simply the maximum amount of data that lwIP will Rx/Tx per packet. This is data payload only, not including headers, etc. I believe anything over 1460 is not possible since this is the maximum allowed (if I'm wrong someone please correct this). I don't believe it has to be a power of 2. Often, on my streaming connection, I'll get some amount of data per packet that is about 700 bytes.
--- On Thu, 8/27/09, Chuck Kuecker <[email protected]> wrote: From: Chuck Kuecker <[email protected]> Subject: RE: [lwip-users] TCP not sending initial ACK To: "Mailing list for lwIP users" <[email protected]> Date: Thursday, August 27, 2009, 10:46 AM I’ve been playing with the TCP options in lwipopts.h. Changing the value of TCP_MSS seems to have an effect on whether or not the initial packet I receive gets ACKed. Is there a tutorial somewhere about what these settings do? I originally had TCP_MSS set to 1500. Is this supposed to be a power of 2? From: [email protected] [mailto:[email protected]] On Behalf Of JM Sent: Thursday, August 27, 2009 6:07 AM To: Mailing list for lwIP users Subject: RE: [lwip-users] TCP not sending initial ACK I'd try a switch anyway, although it's unlikely to fix your problem, but it's easy enough to try. I have not yet tried switching my micro to half duplex, so I can't say if that fixes the hub issue. I will say however that while I was trying to determine what was wrong, the most random things would drastically change how well or bad it worked. Enabling certain sections of debug, changing pbuf sizes, and even what server I was connecting to. My assumption is it was very sensitive to timing. Then again, you said only one packet fails, then it's ok. In my case, things were ok then communications completely broke down. At any rate, I wish you luck. --- On Wed, 8/26/09, Chuck Kuecker <[email protected]> wrote: From: Chuck Kuecker <[email protected]> Subject: RE: [lwip-users] TCP not sending initial ACK To: "Mailing list for lwIP users" <[email protected]> Date: Wednesday, August 26, 2009, 4:02 PM Premature celebration. I changed the processor’s settings to half duplex, and have the identical results. It reliably does not ACK the first packet of the download. I’ve been using the hub for months now, and this is the first time it’s been suspect. There has to be something different about how I handle TCP reception in this part of my code as compared to the other section, where I do TCP reception flawlessly, always. I’ve just got to find it. Chuck From: [email protected] [mailto:[email protected]] On Behalf Of JM Sent: Wednesday, August 26, 2009 12:03 PM To: Mailing list for lwIP users Subject: RE: [lwip-users] TCP not sending initial ACK It only took me 3 -4 weeks to figure this out, but if you're on a hub, try a switch. Apparently if your micro is in full duplex mode, a hub is a no-go. I'm using the LM driver and it works great for receiving lots of data, anyway. Take a look at the "Identification" field in the IP header for all packets going one direction. They should be sequential and incrementing. If there's a gap in the sequence, that means Wireshark isn't displaying a packet that was sent, either because your hardware or OS discarded it. I haven't tried half-duplex yet with the hub again. I'm assuming this would also fix your problem. --- On Wed, 8/26/09, Chuck Kuecker <[email protected]> wrote: From: Chuck Kuecker <[email protected]> Subject: RE: [lwip-users] TCP not sending initial ACK To: "Mailing list for lwIP users" <[email protected]> Date: Wednesday, August 26, 2009, 11:54 AM No, the LWIP timers are called from the main timer tick, and there are no other threads. This is how LWIP is set up for the Luminary driver library I am using, and it has always worked before. Wireshark shows no defective packets. Chuck -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of [email protected] Sent: Wednesday, August 26, 2009 10:34 AM To: Mailing list for lwIP users Subject: Re: [lwip-users] TCP not sending initial ACK Chuck Kuecker wrote: > > I've tried changing the frequency of LWIP interrupt handler calls, > both greatly slowing and speeding them up, with no apparent change in > behavior. > What exactly do you mean with "interrupt handler calls"? The timers? They should *not* be called from an interrupt level: the core code of lwIP may only be accessed from one context at a time! If you obeyed this rule and still have problems, have a look at wireshark packet traces and see if it reports errors in a packet. Also, have a look at the stats (turn them on in lwipopts.h if not already done) and find out whether there are packets dropped. Simon _______________________________________________ lwip-users mailing list [email protected] http://lists.nongnu.org/mailman/listinfo/lwip-users _______________________________________________ lwip-users mailing list [email protected] http://lists.nongnu.org/mailman/listinfo/lwip-users -----Inline Attachment Follows----- _______________________________________________ lwip-users mailing list [email protected] http://lists.nongnu.org/mailman/listinfo/lwip-users -----Inline Attachment Follows----- _______________________________________________ lwip-users mailing list [email protected] http://lists.nongnu.org/mailman/listinfo/lwip-users
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