Re: [lwip-users] Problems with sending UDP packets in FreeRTOS

[Mike Fleetwood]

Hi Simon + Noam,

There is no ARP activity after the first packet is sent.  The current 
software sends to IP_ADDR_BROADCAST, so presumably doesn't generate any 
ARP anyway?

I'm sending data packets every 4mS, so certainly won't be able to queue 
5 seconds-worth.

My software checks for success in buffer creation and allocation before 
continuing, so should not get to the send function if there was not 
enough memory left for the packet buffer.  I would get warnings on my 
"status page" (if HTTP was enabled), but this is not happening.  Also, 
the GPIO toggle markers would indicate if the send was skipped due to 
lack of memory etc.

Many thanks,

Mike.


On 28/07/2016 10:56, Noam Weissman wrote:
> Hi Simon,
>
> I had this problem long ago and as far as I remember packets were not freed
> Or that the sending rate was high and eventually it got into no memory.
>
> As you wrote unsent UDP packets will be freed after 5 seconds but if you send a 
> packet
> every 100ms or so and only have 20-30 buffers 5 seconds will not solve the 
> error.
>
> BR,
> Noam.
>
> -----Original Message-----
> From: lwip-users [mailto:address@hidden On Behalf Of Simon Goldschmidt
> Sent: Thursday, July 28, 2016 12:22 PM
> To: address@hidden
> Subject: Re: [lwip-users] Problems with sending UDP packets in FreeRTOS
>
> Noam Weissman wrote:
> > The reason is that if you send data to a wrong IP or domain and TCP
> > stack does not have the destination MAC address so it will issue ARP
> > messages. What if the ARP message fails ?... The TCP stack does not
> > know where to send the UDP packets. As a result if you continue to
> > send UDP packets they are added to the waiting packets to be sent. They are 
> > never sent, memory is not freed and eventually you are without memory !!
> This is *not* true for lwIP. Pending (unresolved) ARP entries get removed after 
> 5 seconds.
> Queued packets will be freed on removal. If this shouldn't work, please file a 
> bug!
>
>
> Simon
>
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