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Re: [lwip-users] Sending data more than 1472 bytes using UDP

From: Jon Bean
Subject: Re: [lwip-users] Sending data more than 1472 bytes using UDP
Date: Tue, 6 Oct 2020 12:40:27 +0100
User-agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.12.1

Hi Mohammad

I had to do something similar on a TI MCU. I chose to send multiple packets that were less than the MTU. Basically I called the transmit route from the LWIP interrupt. Each time the interrupt was called it would send a data packet that was not more than the MTU. I had some flags to know if I still needed to keep sending data or if I can stop. This seemed to work OK for my application.



On 06/10/2020 12:32, Mohammad Tavakoli wrote:
I made a TCP server on STM32F407 using lwIP version 2.1.2 and it worked fine. Now for some reasons I need to run a UDP server on the MCU. I tried and it worked fine for data size below 1472 bytes. Yet the desired data length is around 16KB to 20KB.
1. I searched and found that IP_FRAG should  be  defined 1 to allow send data over MTU size. It is enabled by default. I read from an email [1] that IP_FRAG_MAX_MTU should be also changed to a proper value. However I cannot realize where it is!
2. Another approach employed by me is to send chopped data whose size are below 1472 bytes in a for loop but the for loop only executes first time and the MCU goes stop status. How I must send data in a for loop?


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