Tutorial: lwip With FreeRTOS and the Freescale FRDM-K64F Board

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Tutorial: lwip With FreeRTOS and the Freescale FRDM-K64F Board

How to create a lwIP project, which is an open source TCP/IP for small systems, using the Kinetis SDK and FreeRTOS on the FRDM-K64F board.

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This tutorial is about how to create a lwIP project with FreeRTOS using the Kinetis SDK V1.3.0 with Kinetis Design Studio on the Freescale FRDM-K64F board.

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I would like to thank Frank Bargstedt for providing me the many hints and steps for this tutorial. Without his contribution I think I would not have been able to create this article. THANK YOU!


lwIP is a small Open Source TCP/IP implementation suitable for small systems. The project can be found on http://savannah.nongnu.org/projects/lwip/. The Kinetis SDK comes with an lwIP port which I’m going to use in this project. The goal is to create a project with lwIP and FreeRTOS running on the FRDM-K64F board.


For this project I assume you have the following available/installed (see links at the end of this article):

  1. Freescale Kinetis Design Studio (KDS) V3.0.0. Alternatively stock Eclipse with Processor Expert installed (see “Going to Mars: Building a DIY Eclipse IDE for ARM Embedded Microcontrollers“) can be used.
  2. Freescale Kinetis SDK (KSDK) V1.3.0 and Kinetis SDK Eclipse update installed in Eclipse/KDS
  3. McuOnEclipse components Components 2015-10-17.zip or later
  4. FRDM-K64F board with cables, connected to a router with DHCP

Project Creation

In KDS, use the menu File > New > Kinetis Project to create a new project.

Provide a name for the project:

Creating Project

Select the board:

Selecting FRDM-K64F Board

Select the Kinetis SDK with Processor Expert enabled:

KSDK v1.3.0 Processor Expert Project

Then finish, and the proejct is created.

Pin Settings

The next step is to check the pin muxing and pin settings:


By default the ENET pins are not routed:

Default ENET Pins

In a first step have all pins routed:

Routed ENET Pins

Next we have to configure the RMII0_MDIO pin: for this we use the context menu on that pin and select ‘Pin Functional Properties’:

Context menu on RMII0_MDIO

Configure the pin for slow slew rate, enabled open drain, low drive strength, disabled passive filter, pull-up selection with enabled pull-up as below:

Pin Electrical Properties

:!: Important: without the above settings the ENET will not properly work!

fsl_enet Component

Next, add the fsl_enet SDK component from the Components Library to the project:

Adding fsl_enet component

This adds the component to the project. It’s settings can be at the default settings.

fsl_enet added to project

Clock Configuration

In this section the clock gets configured. It is important that the clock is in sync with the PHY clock which runs at 50 MHZ. The settings I need to check are in the Clock Manager:

Clock Manager

By default, the project has multiple clock configurations (which are a waste of code and RAM!):

Clock Configurations

Clicking into the line and using the ‘-‘ icon I can remove the configurations:

Removing Clock Configurations

I reduce it to only one and set it as the Init clock Configuration:

Reduced number of clock configurations

That configuration I set to maximum clock speed with the 50 MHz clock source:

  • Clock source: External Reference Clock with 50 MHz from EXTAL0
  • MGG Mode set to PEE
  • PLL output set to 120 MHz
  • Core Clock set to 120 MHz
  • Bus Clock set to 60 MHz
  • External Bus Clock set to 40 MHz
  • Flash Clock set to 24 MHz

Clock Management Settings


The default OS abstraction in the Kinetis SDK v1.3.0 comes with unnecessary overhead, so it needs some configuration:


I disable the OS Timers for bare metal mode as they are not needed:

Disabled OS Timers


Next, FreeRTOS gets added. I’m *not* using the FreeRTOS component which comes with the Kinetis SDK V1.3.0 as it is an older version and does not support advanced features like RTT Tracing (see “ Search Using Segger Real Time Terminal (RTT) with Eclipse“).

So I’m using the McuOnEclipse FreeRTOS component from the repository:

Adding McuOnEclipse FreeRTOS component

This adds FreeRTOS plus the Utility component to the project:

Added FreeRTOS

FreeRTOS gets configured as below:

  1. To prepare the RTOS to work with the Kinetis SDK, enable the SDK option and add the Kinetis SDK component to it: Enabled Kinetis SDK for RTOSEnabled Kinetis SDK for RTOS
  2. Verify the ARM CPU used, in the case of the FRDM-K64F it is an ARM Cortex-M4F with floating point support: Kinetis ARM Family SettingKinetis ARM Family Setting
  3. As the rest of the SDK is using malloc()/free() too, I set the RTOS memory allocation to Scheme 3 too, with an appropriate Heap Size: Memory Allocation SchemeMemory Allocation Scheme

In the compiler preprocessor settings (menu Project > Properties) I need to tell the SDK that I’m using FreeRTOS with a define:


Added FSL_RTOS_FREE_RTOS Compiler Preprocessor Define

Generating Processor Expert Code

With all the components configured, I can generate Processor Expert code:

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Generating Processor Expert Code

If this requires some file changes, a confirmation dialog might show up which I confirm with OK:

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Confirm File Changes

PHY Driver

The FRDM-K64F uses the ‘ksz8081’ PHY. To add the driver for it to my project I copy the following files

  • fsl_phy_driver.c
  • fsl_phy_driver.h



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PHY Drivers

and add them to my project Sources folder:

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Added PHY Driver


I would like to use semihosting (see “Semihosting for Kinetis Design Studio V3.0.0 and GNU ARM Embedded (launchpad)“) to write messages to the debugger console instead of using a physical UART.

First, I add a file ‘fsl_debug_console.h’ to the sources:

which has defines to map debug printf calls to the normal printf:

 * fsl_debug_console.h
 * Map printf for semihosting implementation.


#define PRINTF printf
#define debug_printf printf


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fsl_debug_console added to project

To tell the linker that I’m using semihosting, I use the following linker commands:

-specs=rdimon.specs -specs=nano.specs

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Semihosting Linker Commands

Kinetis SDK Utilities

The Kinetis SDK utilities and internal printf routines do not play well with semihosting, so I had to disable it:

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Disabled SDK utilities

This can be easily done with using the context menu on that folder and exclude the resource from build:

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Excluded from Build


In this step the lwIP stack gets added to the project. There is a port of lwIP inside the Freescale Kinetis SDK V1.3.0 folder:

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lwIP in the Kinetis SDK V1.3.0

Copy the lwip folder into the project root folder:

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lwip added to project

I’m not going to use IPV6, so I delete the ipv6 folders, otherwise I will get compilation errors with both ipv6 and ipv4 active:

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ipv6 removed

In order to the compiler to find all the header files, I’m adding the following include paths to the compiler settings:


I can copy-paste paths settings to the dialog in Eclipse.

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lwip include paths

Application Code

As application code I add this to main.c:

#define DHCP_TIMEOUT 10

#include "lwip/api.h"
#include "lwip/tcpip.h"
#include "lwip/udp.h"
#include "lwip/dhcp.h"
#include "netif/etharp.h"
#include "ethernetif.h"

#include <string.h>
#include <stdio.h>
/* providing a debug_printf() to make the linker happy */
int debug_printf(const char *fmt_s, ...)
#if 0
 va_list ap;
 int result;
 /* Do nothing if the debug uart is not initialized.*/
 if (s_debugConsole.type == kDebugConsoleNone)
 return -1;
 va_start(ap, fmt_s);
 result = _doprint(NULL, debug_putc, -1, (char *)fmt_s, ap);

 return result;
 return -1;

#if 1 /* depending on the GNU tools and libraries, a custom _sbrk() is needed */
void *_sbrk ( uint32_t delta ) {
extern char end; /* Defined by the linker */
static char *heap_end;
char *prev_heap_end;

 if (heap_end == 0) {
 heap_end = &end;

 prev_heap_end = heap_end;
 heap_end += delta;
 return (void *) prev_heap_end;

static void LwipInitTask(void* pvArguments) {
 err_t err;
 struct netif fsl_netif0;
 ip_addr_t fsl_netif0_ipaddr, fsl_netif0_netmask, fsl_netif0_gw;

 char msg[] = "This is my message";


 // Init lwip stack
 printf("%s: lwip init called ..\n", __FUNCTION__);

 // Setup IP Config for DHCP ...
 IP4_ADDR(&fsl_netif0_ipaddr, 0,0,0,0);
 IP4_ADDR(&fsl_netif0_netmask, 0,0,0,0);
 IP4_ADDR(&fsl_netif0_gw, 0,0,0,0);

 /* Add a network interface to the list of lwIP netifs. */
 netif_add(&fsl_netif0, &fsl_netif0_ipaddr, &fsl_netif0_netmask, &fsl_netif0_gw, NULL, ethernetif_init, ethernet_input);
 /* Set the network interface as the default network interface. */
 /* obtain the IP address, default gateway and subnet mask by using DHCP*/
 err = dhcp_start(&fsl_netif0);

 printf("%s : Started DCHP request (%s)\n", __FUNCTION__, lwip_strerr(err));

 for(int i=0; i < DHCP_TIMEOUT && fsl_netif0.dhcp->state != DHCP_BOUND; i++) {
 printf("%s : Current DHCP State : %d\n", __FUNCTION__, fsl_netif0.dhcp->state);
 // Wait a second

 // Make it active ...

 printf("%s : Interface is up : %d\n", __FUNCTION__, fsl_netif0.dhcp->state);
 printf("%s : IP %s\n", __FUNCTION__, ipaddr_ntoa(&fsl_netif0.ip_addr));
 printf("%s : NM %s\n", __FUNCTION__, ipaddr_ntoa(&fsl_netif0.netmask));
 printf("%s : GW %s\n", __FUNCTION__, ipaddr_ntoa(&fsl_netif0.gw));

 if (fsl_netif0.dhcp->state == DHCP_BOUND) {
 // Send out some UDP data
 struct netconn* pConnection;

 // Create UDP connection
 pConnection = netconn_new(NETCONN_UDP);
 // Connect to local port
 err = netconn_bind(pConnection, IP_ADDR_ANY, 12345);
 printf("%s : Bound to IP_ADDR_ANY port 12345 (%s)\n", __FUNCTION__, lwip_strerr(err));

 err = netconn_connect(pConnection, IP_ADDR_BROADCAST, 12346 );
 printf("%s : Connected to IP_ADDR_BROADCAST port 12346 (%s)\n", __FUNCTION__, lwip_strerr(err));

 for(int i = 0; i < 10; i++ ){
 struct netbuf* buf = netbuf_new();
 void* data = netbuf_alloc(buf, sizeof(msg));

 memcpy (data, msg, sizeof (msg));
 err = netconn_send(pConnection, buf);
 printf("%s : Sending to IP_ADDR_BROADCAST port 12346 (%s)\n", __FUNCTION__, lwip_strerr(err));

 netbuf_delete(buf); // De-allocate packet buffer

 // Wait a second

 err = netconn_disconnect(pConnection);
 printf("%s : Disconnected from IP_ADDR_BROADCAST port 12346 (%s)\n", __FUNCTION__, lwip_strerr(err));

 err = netconn_delete(pConnection);
 printf("%s : Deleted connection (%s)\n", __FUNCTION__, lwip_strerr(err));
 // Wait a second

 /* finish the lease of the IP address */
 err = dhcp_release(&fsl_netif0);
 printf("%s : DHCP Release (%s)\n", __FUNCTION__, lwip_strerr(err));

 for(;;) {};

And call it inside main() like below. An important point is that the MPU of the K64F needs to be disabled:

 printf("Welcome to the world of lwip!\r\n");

 /* Disable the mpu */

 /* create lwIP initialization task */
   configMINIMAL_STACK_SIZE * 4,

After that, the RTOS gets started with vTaskStartScheduler().

Example Session

With this, I can build, download and debug the application. With the network cable plugged in, the application writes the status to the semihosting console. It starts with a DHCP request and then does some IP broadcasts and at the end releases the address and closes the connection:

Welcome to the world of lwip!
LwipInitTask: lwip init called ..
LwipInitTask : Started DCHP request (Ok.)
LwipInitTask : Current DHCP State : 6
LwipInitTask : Current DHCP State : 6
LwipInitTask : Current DHCP State : 6
LwipInitTask : Current DHCP State : 8
LwipInitTask : Interface is up : 10
LwipInitTask : IP
LwipInitTask : NM
LwipInitTask : GW
LwipInitTask : Bound to IP_ADDR_ANY port 12345 (Ok.)
LwipInitTask : Connected to IP_ADDR_BROADCAST port 12346 (Ok.)
LwipInitTask : Sending to IP_ADDR_BROADCAST port 12346 (Ok.)
LwipInitTask : Sending to IP_ADDR_BROADCAST port 12346 (Ok.)
LwipInitTask : Sending to IP_ADDR_BROADCAST port 12346 (Ok.)
LwipInitTask : Sending to IP_ADDR_BROADCAST port 12346 (Ok.)
LwipInitTask : Sending to IP_ADDR_BROADCAST port 12346 (Ok.)
LwipInitTask : Sending to IP_ADDR_BROADCAST port 12346 (Ok.)
LwipInitTask : Sending to IP_ADDR_BROADCAST port 12346 (Ok.)
LwipInitTask : Sending to IP_ADDR_BROADCAST port 12346 (Ok.)
LwipInitTask : Sending to IP_ADDR_BROADCAST port 12346 (Ok.)
LwipInitTask : Sending to IP_ADDR_BROADCAST port 12346 (Ok.)
LwipInitTask : Disconnected from IP_ADDR_BROADCAST port 12346 (Ok.)
LwipInitTask : Deleted connection (Ok.)
LwipInitTask : DHCP Release (Ok.)

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lwip session


A long-time-waiting thing on my to-do list finally has been accomplished: It takes many pieces to build the basis of a network IP application, and lwip for sure is a good and well documented open source project. With the help of Processor Expert many aspects of the networking application get simplified, and after some tweaks the Kinetis SDK is now working too.

The project created in this tutorial is on GitHub: https://github.com/ErichStyger/mcuoneclipse/tree/master/Examples/KDS/FRDM-K64F120M/FRDM-K64F_lwIP_FreeRTOS.

freertos, freescale, iot

Published at DZone with permission of Erich Styger , DZone MVB. See the original article here.

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