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Re: [lwip-users] R: ping slow down

From: Greg Smith
Subject: Re: [lwip-users] R: ping slow down
Date: Tue, 31 May 2016 14:46:42 +0000

Hi, Rastislav.
I had a similar problem with ping times using PPP in the 2.0.0 Beta1 release and FreeRTOS 8.2.3 on an STM32F2xx part (Cortex-M3). I'm not using Ethernet (I'm using serial), but I eventually tracked it down to interrupt priority and interrupt levels.

For me, my USART IRQ was very, very low by default. Once I increased its priority (to about half way in the middle of all priorities), that really cut back on the latency and reduced ping times.

I also found I had the value of configMAX_SYSCALL_INTERRUPT_PRIORITY in FreeRTOSConfig.h set too high (which means a low priority). Once I increased the priority (by lowering the value) to a range that made sense -- I needed the priority high enough that the interrupt would complete before RTOS functions I called would get handled -- then that was the final piece. I can now ping for hours and the total turnaround time is 5-6ms on my setup, which is right where I want it to be.

I don't know if any of that applies to your situation, but just a couple things to check.

-- G

> -----Original Message-----
> From: lwip-users
> On Behalf Of Rastislav Uhrin
> Sent: Monday, 30 May 2016 17:27
> To: Mailing list for lwIP users <address@hidden>
> Subject: [lwip-users] R: ping slow down
> Thank you for answering.
> This task waits on semaphore from interrupt routine which is invoked when Eth
> frame is received.
> The driver is form Infineon.
> Port to RTOS should be OK because I have compared many I found on internet and
> they are all the same.
> OK. I will investigate further.
> rum
> -----Messaggio originale-----
> Da: lwip-users [mailto:lwip-users-
> address@hidden Per conto di Sergio R.
> Caprile
> Inviato: lunedì 30 maggio 2016 23:07
> A: address@hidden
> Oggetto: Re: [lwip-users] ping slow down
> And that task runs every...
> >> Most likely your code is polling at regular intervals and what you
> >> see as varying delay is the phase difference of your ping frequency
> >> and your poll frequency "signals".
> Try to move pins every time that task runs Try to move pins every time you see
> a packet, and check on a scope Read the wiki and see if you are doing things
> right for an RTOS-based port
> http://lwip.wikia.com/wiki/Writing_a_device_driver
> http://lwip.wikia.com/wiki/Porting_for_an_OS
> Make sure you don't call low level routines from interrupt code, all non socket
> nor netconn calls must be on the same thread.
> No, it is not normal to have delays unless something is causing those delays.
> lwIP is mostly event driven, when a frame comes in and you notice that, you
> send it to lwIP and it peels protocol by protocol until it either calls you
> (RAW API)/delivers to netconn/socket (which I don't
> master) or responds itself (ping).
> If it does not responds itself asap is because you don't give it the frame or
> you don't let it run fast enough to do its job.
> You can also check for known caveats with your port to your RTOS.
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