Hi all - Back to look at this delay issue. Update:
I studied the driver and ST-provided FreeRTOS/LwIP/cmsis glue and all
looks AOK,
unlike the extremely buggy code ST provides for ST32F7xx series.
Again, after a lost packet, the host (PC running Windows 10) issues a
_*single*_ duplicate-ack and waits.
LwIP receives the single duplicate ack and by design _*ignores it*_
(tcp_in.c lines 1207-1227).
LwIP takes two passes through slow_tmr (.5 sec intervals) before
retransmitting the lost packet.
Hence nasty >1 second delay.
I tried patching LwIP to _immediately_ retransmit on a duplicate ack
(line 1215):
if (pcb->dupacks >= 1 /* DRN kludge prevents 1+sec delays
after lost packet, should be: 3 */) {
/* Do fast retransmit (checked via TF_INFR, not via
dupacks count) */
tcp_rexmit_fast(pcb);
}
Wireshark shows a TCP out-of-order packet, which it did not do unpatched
(after the 1.5 sec delay):
http://www.nadler.com/backups/20190503_Lwip_pause_kludgeFix.pcapng
Is this OK? Or is there something wrong in tcp_rexmit_fast?
The client picks up and continues happily regardless and I get the
desired through-put with no problematic long pauses...
Thanks!
Best Regards, Dave
On 3/15/2019 5:56 PM, Dave Nadler wrote:
To recap: LwIP 2.1.2 on FreeRTOS 9, ST32F429, IPv4, TCP.
I want to see how much I can consistently push through the stack.
Made a simple test server (sockets API) which repeatedly outputs
101-character lines.
I access the server via PuTTY raw mode on Winbloze over a local network.
I can usually send 3 lines per msec for a second (3000 lines in 1
second), but...
Sometimes, I get ~ 1-second pauses (as seen in Putty or TeraTerm).
Here's the capture:
http://www.nadler.com/backups/20190227_Lwip_pause.pcapng
Everything is going swimmingly until 4316.
The windows client notes a missing segment and issues a duplicate ACK
as expected.
This exact pattern is quite repeatable.
FreeRTOS is running happily during the evil pause (LED blinky task
uninterrupted).
Why does the LwIP application take ~1.5 seconds to retransmit the data?
Again, thanks for your time and any hints...
Best Regards, Dave
--
Dave Nadler, USA East Coast voice (978) 263-0097, d...@nadler.com, Skype
Dave.Nadler1
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