Quality RTOS & Embedded Software

 Real time embedded FreeRTOS RSS feed 
Quick Start Supported MCUs PDF Books Trace Tools Ecosystem


FreeRTOS + TCP and ARP info

Posted by dsherman26 on September 8, 2017

I've been working on getting FreeRTOS + TCP working on a Freescale Kinetis K60 tower board. I have DHCP working and I can get an IP address from a DSL modem I'm using as the DHCP host (COMTREND CT-5374). I can see the tower boards DHCP address in the router's DHCP table, but the ARP table does not show the tower board. Is there some step I need to do to make the router aware of it? I can't ping it because the router reports that it is unaware of the IP address.

FreeRTOS + TCP and ARP info

Posted by heinbali01 on September 10, 2017

Hi Dave, it is difficult to see from a distance why you can not ping your device.

In my own testing environment, I have devices behind a router with WAN/LAN, as well as behind a LAN switch.

If you have a switch, I would try that first: either with a fixed IP-address, or by running a DHCP server on your laptop.

Have you also tried without DHCP?

#define ipconfigUSE_DHCP	0

Can you confirm that your laptop and your "tower board" have the same network address? For instance and ?

It would be very strange if a router does not pass ARP messages between the LAN ports ( "ETH1" to "ETH4" ). Also the device will send-out so-called gratuitous ARP messages every 20 seconds:

#define arpGRATUITOUS_ARP_PERIOD       ( pdMS_TO_TICKS( 20000 ) )

These packet help detecting IP-address conflicts. A switch or a LAN router must forward these packets as well and you should see them when running WireShark.

I would also check the properties of "ETH1" to "ETH4" in the router's setup-page. Does the router allow communication between those ports?

FreeRTOS + TCP and ARP info

Posted by dsherman26 on November 2, 2017

Thank you, sorry for the delay getting back. I figured out it was because the stack was replying to the arp request at the beginning of the ping, and sending the arp information back. The hardware was configured to add the checksum, but I had to make sure the checksum was zeroed before replying, otherwise the hardware would get the checksum wrong. The arp table I'm not sure of, the router still does not show it, although I can ping it now.

[ Back to the top ]    [ About FreeRTOS ]    [ Privacy ]    [ Sitemap ]    [ ]

Copyright (C) Amazon Web Services, Inc. or its affiliates. All rights reserved.

Latest News

NXP tweet showing LPC5500 (ARMv8-M Cortex-M33) running FreeRTOS.

Meet Richard Barry and learn about running FreeRTOS on RISC-V at FOSDEM 2019

Version 10.1.1 of the FreeRTOS kernel is available for immediate download. MIT licensed.

View a recording of the "OTA Update Security and Reliability" webinar, presented by TI and AWS.


FreeRTOS and other embedded software careers at AWS.

FreeRTOS Partners

ARM Connected RTOS partner for all ARM microcontroller cores

Espressif ESP32

IAR Partner

Microchip Premier RTOS Partner

RTOS partner of NXP for all NXP ARM microcontrollers


STMicro RTOS partner supporting ARM7, ARM Cortex-M3, ARM Cortex-M4 and ARM Cortex-M0

Texas Instruments MCU Developer Network RTOS partner for ARM and MSP430 microcontrollers

OpenRTOS and SafeRTOS

Xilinx Microblaze and Zynq partner