Re: [lwip-users] Help with LwIP Modem

[Jaime Fernandez Hoffiz]

Hi All,

To close the loop on my original question maybe it can help another rookie
like me.

My goal was to set my ethernet device so that it will act as a cable,
received packets from the netif, modulates them, send them over a cable,
have another device demod, the exact same packet, and last transmit the
packet out over its netif.

My initialization changed from:

// netif->flags = NETIF_FLAG_BROADCAST | NETIF_FLAG_ETHARP |
NETIF_FLAG_IGMP;
netif->flags = 0;

Now I'm able to receive all incoming packets but not answer or react to any
of them. For example, if I ping the target I see the packet but lwip does
not ack and replies back.

Thanks all for the help and suggestions.

Jaime

On Sat, Jul 9, 2016 at 3:30 PM, Jeff Barlow  wrote:

> On 07/09/2016 12:10 PM, goldsi...@gmx.de wrote:
>
>> Jeff Barlow wrote:
>>
>>> I think you will find that ChibiOS does much the same. The reasoning
>>> as I understand it is to keep ISR code paths as short as possible to
>>> minimize latency in hard real time systems.
>>>
>>
>> Without knowing ChibiOS in detail, I'd be interested in knowing what
>> would be the actual penalty of removing the need for the API user to
>> supply the "bool inIsr"...
>>
>
> I don't claim to be an expert on ChibiOS in particular. It seems fairly
> obvious to me though that inserting extra code in the ISR path that inspect
> some globals only to figure out that it is indeed in an ISR will have an
> adverse effect on latency. ChibiOS is very tightly tuned to minimize
> latency. For some of us this makes the difference between a working system
> and one that almost works.
>
> --
> Later,
> Jeff
>
>
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[lwip-users] Netconn write and non-blocking

[Jan]

Dear all,

What is the best way to handle the following situation when using netconn in
TCPIP mode and v2.0.0RC1. 

If I connect (with netconn_connect() ) to a device that's not available and
netconn is blocking how long do I have to wait? 

Because it's unknown to me and it could take very long I decided to use the
"netconn_set_nonblocking(conn, 1)" so I can delete the connection if it
takes to long to connect. 

But when the device is available I cannot use the netconn_write() (the
function returns ERR_VAL). In the command it says:

/* This implies netconn_write() cannot be used for non-blocking send,
since
   it has no way to return the number of bytes written. */

How can I use netconn_write() in a non-blocking situation?



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Re: [lwip-users] lwIP delays outgoing TCP packets by up to 500ms

[Joel Cunningham]

It's worth comparing the behavior of the netconn API.  Even though the netconn 
API is only available with NO_SYS = 0, it is still a user of the raw API like 
the applications mentioned in this email thread.



lwip_netconn_do_writemore() calls tcp_write() until all segments have been put 
into the TCP send buffer, then calls tcp_output().



Joel


On Jul 13, 2016, at 10:36 AM, Pîrvu Mihai  wrote:


Again, it's probably not be the wrong approach, it's just what I've been told 
on this thread:


https://lists.gnu.org/archive/html/lwip-users/2016-06/msg00055.html



Since it worked for me at that moment, I just let it like that, and reading the 
responses here confirms that it's the correct approach if you don't want to 
wait for the delay.


Mihai


On Wed, Jul 13, 2016 at 5:59 PM, Jakub Schmidtke  wrote:


I think you might have missed reading the documentation: tcp_write enqueue 
data, tcp_outout tries to send it. You always have to call both.




I actually found the recommended call flow on wiki (Here: 
http://lwip.wikia.com/wiki/Raw/TCP ) after Mihai mentioned using tcp_output().

And yes, I haven't fully read the docs/wiki yet, since I am trying to fix 
existing code written by someone else - who must have missed that...


However, Mihai mentions that calling tcp_output() might be the wrong 
approach... Is it really?


Thanks!

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Re: [lwip-users] lwIP delays outgoing TCP packets by up to 500ms

[Pîrvu Mihai]

Again, it's probably not be the wrong approach, it's just what I've been
told on this thread:

https://lists.gnu.org/archive/html/lwip-users/2016-06/msg00055.html

Since it worked for me at that moment, I just let it like that, and reading
the responses here confirms that it's the correct approach if you don't
want to wait for the delay.

Mihai

On Wed, Jul 13, 2016 at 5:59 PM, Jakub Schmidtke  wrote:

> I think you might have missed reading the documentation: tcp_write enqueue
>> data, tcp_outout tries to send it. You always have to call both.
>>
>> I actually found the recommended call flow on wiki (Here:
> http://lwip.wikia.com/wiki/Raw/TCP ) after Mihai mentioned using
> tcp_output().
> And yes, I haven't fully read the docs/wiki yet, since I am trying to fix
> existing code written by someone else - who must have missed that...
>
> However, Mihai mentions that calling tcp_output() might be the wrong
> approach... Is it really?
>
> Thanks!
>
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Re: [lwip-users] 0MQ, MQTT and RabbitMQ

[Sergio R. Caprile]

Hi,
I contributed the transport abstraction for the Packet libraries for 
MQTT and MQTT-SN in Paho for embedded.
I've been working on the transport for MQTT-SN to use the lwIP RAW API, 
which seemed to be working, but I didn't submit them to Paho.

I can post it if you or anyone else are willing to try it and comment.
MQTT is perhaps more involved as it requires a permanent connection and 
that is probably not very embedded, but I plan to write examples for 
MQTT anyway, it is just that I'll be more likely using MQTT-SN and time 
is a scarce resource these days.


Paho:
org.eclipse.paho.mqtt.embedded-c
org.eclipse.paho.mqtt-sn.embedded-c

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Re: [lwip-users] lwIP delays outgoing TCP packets by up to 500ms

[Jakub Schmidtke]

>
> I think you might have missed reading the documentation: tcp_write enqueue
> data, tcp_outout tries to send it. You always have to call both.
>
> I actually found the recommended call flow on wiki (Here:
http://lwip.wikia.com/wiki/Raw/TCP ) after Mihai mentioned using
tcp_output().
And yes, I haven't fully read the docs/wiki yet, since I am trying to fix
existing code written by someone else - who must have missed that...

However, Mihai mentions that calling tcp_output() might be the wrong
approach... Is it really?

Thanks!
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Re: [lwip-users] lwIP delays outgoing TCP packets by up to 500ms

[Sergio R. Caprile]

Confusion might arise from the examples in contrib, neither tcpecho_raw 
nor smtp do call tcp_output(). Not everyone seems to look at httpd... 
nor read the wiki, nor the docs...


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[lwip-users] 0MQ, MQTT and RabbitMQ

[Abdul Hakeem]

Hello,

Could anyone share their experience(s) of any integration of  LWIP with OMQ,
MQTT and RabbitMQ.

Much obliged,

Abdul Hakeem



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Re: [lwip-users] lwIP delays outgoing TCP packets by up to 500ms

[goldsimon]

I think you might have missed reading the documentation: tcp_write enqueue 
data, tcp_outout tries to send it. You always have to call both.


Simon


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Am 13. Juli 2016 2:35:59 nachm. schrieb Jakub Schmidtke :



Maybe your sys_now() or sys_jiffies() functions are too course?
They should have a resolution of approx. 1 msec.



I am not even talking about observed delays.
I am looking at the code, and based on that, those packets will be delayed
by up to twice the value of TCP_TMR_INTERVAL in milliseconds.
TCP_TMR_INTERVAL is set, by default, to 250.

The TCP timer is scheduled to run every TCP_TMR_INTERVAL milliseconds.
Actually every TCP_TMR_INTERVAL values returned by sys_now(),
which is supposed to return milliseconds. That timer calls tcp_tmr(), which
will always call tcp_fasttmr() and call tcp_slowtmr() every other time.
Even the comments in tcp_tmr() say that tcp_slowtmr() will be called every
500ms.

And I am looking at tcp_write(). It is a pretty big function so I may be
missing something,
but it doesn't look like it's actually sending any of the packets being
written,
it just appends them to 'unsent' queue.

The actual writing happens inside tcp_slowtmr() which, again, is called
every 500ms.
So if something is written using tcp_write() 10ms after tcp_slowtmr()
triggered,
it will be actually sent out 490ms later. Even assuming perfect resolution
of sys_now
and being able to call things at exactly the right time. It's still up to a
half a second later!
Which is the problem I am experiencing.

Now I could modify TCP_TMR_INTERVAL to much lower value,
and call sys_check_timeouts() much more often to cause tcp_slowtmr() to be
called much more frequently.

Or modify sys_now() to return values that don't represent milliseconds but
something smaller
(and still call sys_check_timeouts() more often), but this changes the
whole time scale and I have no idea
what other effects this might have.

Both of these solutions feel ugly and could affect the performance.

I even tried calling tcp_slowtmr() manually, and it seems to send out those
TCP packets
sooner, but it doesn't feel like the right solution.

I haven't looked into manually calling tcp_output after each tcp_write as
suggested in an earlier response yet,
but the same response also says that it's a wrong thing to do...

That is why I am asking if I am missing something...

But depending on your hardware it could not be so easy to accomplish. BTW,

what is your hardware?



I am running it as a part of  a system that generates IP packets in
software.
Right now I am running it on a powerful i5 machine, so performance is not
an issue.



I've myself built with NO_SYS=1 on djgpp/MSDOS with no long delays
as you describe. Hence I think it's a problem with your 'clock-tick'
function.



What is your TCP_TMR_INTERVAL?
What do you return in sys_now()?


Thanks!



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Re: [lwip-users] lwIP delays outgoing TCP packets by up to 500ms

[Jakub Schmidtke]

>
> Maybe your sys_now() or sys_jiffies() functions are too course?
> They should have a resolution of approx. 1 msec.


I am not even talking about observed delays.
I am looking at the code, and based on that, those packets will be delayed
by up to twice the value of TCP_TMR_INTERVAL in milliseconds.
TCP_TMR_INTERVAL is set, by default, to 250.

The TCP timer is scheduled to run every TCP_TMR_INTERVAL milliseconds.
Actually every TCP_TMR_INTERVAL values returned by sys_now(),
which is supposed to return milliseconds. That timer calls tcp_tmr(), which
will always call tcp_fasttmr() and call tcp_slowtmr() every other time.
Even the comments in tcp_tmr() say that tcp_slowtmr() will be called every
500ms.

And I am looking at tcp_write(). It is a pretty big function so I may be
missing something,
but it doesn't look like it's actually sending any of the packets being
written,
it just appends them to 'unsent' queue.

The actual writing happens inside tcp_slowtmr() which, again, is called
every 500ms.
So if something is written using tcp_write() 10ms after tcp_slowtmr()
triggered,
it will be actually sent out 490ms later. Even assuming perfect resolution
of sys_now
and being able to call things at exactly the right time. It's still up to a
half a second later!
Which is the problem I am experiencing.

Now I could modify TCP_TMR_INTERVAL to much lower value,
and call sys_check_timeouts() much more often to cause tcp_slowtmr() to be
called much more frequently.

Or modify sys_now() to return values that don't represent milliseconds but
something smaller
(and still call sys_check_timeouts() more often), but this changes the
whole time scale and I have no idea
what other effects this might have.

Both of these solutions feel ugly and could affect the performance.

I even tried calling tcp_slowtmr() manually, and it seems to send out those
TCP packets
sooner, but it doesn't feel like the right solution.

I haven't looked into manually calling tcp_output after each tcp_write as
suggested in an earlier response yet,
but the same response also says that it's a wrong thing to do...

That is why I am asking if I am missing something...

But depending on your hardware it could not be so easy to accomplish. BTW,
> what is your hardware?
>

I am running it as a part of  a system that generates IP packets in
software.
Right now I am running it on a powerful i5 machine, so performance is not
an issue.


> I've myself built with NO_SYS=1 on djgpp/MSDOS with no long delays
> as you describe. Hence I think it's a problem with your 'clock-tick'
> function.
>

What is your TCP_TMR_INTERVAL?
What do you return in sys_now()?


Thanks!
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Re: [lwip-users] lwIP delays outgoing TCP packets by up to 500ms

[Gisle Vanem]

Jakub Schmidtke wrote:

> I am using lwip with NO_SYS=1, and I have noticed
> that outgoing TCP packets are very delayed.
> 
> It looks like between writing a packet (using tcp_write),
> and the time it actually written to the interface it takes usually about 
> 200ms.

Maybe your sys_now() or sys_jiffies() functions are too course?
They should have a resolution of approx. 1 msec. But depending on your
hardware it could not be so easy to accomplish. BTW, what is your hardware?

I've myself built with NO_SYS=1 on djgpp/MSDOS with no long delays
as you describe. Hence I think it's a problem with your 'clock-tick'
function.

-- 
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Re: [lwip-users] lwIP delays outgoing TCP packets by up to 500ms

[Pîrvu Mihai]

I've worked around this disabling Nagle Algorithm for each pcb and also
calling tcp_output after every write. But somebody told me it was the wrong
approach doing so, but it works for me so I don't know what to say.

Mihai

On Wed, Jul 13, 2016 at 3:20 AM, Jakub Schmidtke  wrote:

> Hi,
>
> I am using lwip with NO_SYS=1, and I have noticed
> that outgoing TCP packets are very delayed.
>
> It looks like between writing a packet (using tcp_write),
> and the time it actually written to the interface it takes usually about
> 200ms.
>
> I examined the code, and it looks like lwip only writes regular packets
> every 500ms.
>
> Basically tcp_write only adds segments to a list, and they are only
> actually sent inside tcp_slowtmr.
> Which, by default, is only called once every two calls to tcp_tmr().
> Which gets called every 250ms, so the data being written with tcp_write
> will be sent out up to 500ms later.
>
> This is a really, really long time!
>
> Am I missing something?
>
>
> Thanks!
>
>
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