LPC1768 Cortex M3 CrossWorks Demo
Including Embedded Web Server and USB Examples
[Embedded Ethernet Examples]

Buy the LPC17xx edition of the FreeRTOS tutorial eBook or paperback.

This page presents a Rowley CrossWorks FreeRTOS web server and USB demo that is pre-configured to run on the Keil MCB1700 evaluation board. The MCB1700 uses an LPC1768 Cortex M3 microcontroller from NXP.

The demo uses:

• The FreeRTOS GCC Cortex-M3 port.
• The Rowley CrossWorks IDE version 2.0.
• Adam Dunkels open source uIP embedded TCP/IP stack to implement a web server with CGI scripting.
• Bertrik Sikkens open source LPCUSB USB stack to implement a CDC class echo server.

I tested the development environment using both an Amontec JTAGKey-Tiny and a CrossConnect for ARM. Both worked well, although the Amontec device was many times slower.

uIP and LPCUSB are licensed separately from FreeRTOS. Users must familiarise themselves with the uIP and LPCUSB licenses respectively.

FreeRTOS has made some modifications to the uIP stack since this demo was created. See the Embedded Ethernet Examples List page for more information.

The FreeRTOS Cortex M3 port includes a full interrupt nesting model. Interrupt priorities must be set in accordance with the instructions on the Customisation page for correct operation.

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IMPORTANT! Notes on using the NXP Cortex-M3 Web Server Demo

Please read all the following points before using this RTOS port.

1. Source Code Organisation
2. The Demo Application
3. RTOS Configuration and Usage Details

See also the FAQ My application does not run, what could be wrong?

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Source Code Organisation

The CrossWorks project for the LPC1768 demo is called RTOSDemo.hzp and is located in the FreeRTOS/Demo/CORTEX_LPC1768_GCC_Rowley directory.

The FreeRTOS zip file download contains the files for all the ports and demo application projects. It therefore contains many more files than used by this demo. See the Source Code Organization section for a description of the downloaded files and information on creating a new project.

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The Demo Application

web server configuration

Connect the MCB1700 target to a computer running a web browser either directly using a point to point (crossover) cable, or via a Ethernet switch using a standard Ethernet cable.

The IP address used by the demo is set by the constants configIP_ADDR0 to configIP_ADDR3 within the file FreeRTOS/Demo/CORTEX_LPC1768_GCC_Rowley/FreeRTOSConfig.h. The MAC address and net mask are configured within the same header file.

The IP addresses used by the web browser computer and the MCB1768 development board must be compatible. This can be ensured by making the first three octets of both IP addresses identical. For example, if the web browser computer uses IP address 192.168.100.1, then the development board can be given any address in the range 192.168.100.2 to 192.168.100.254 (barring any addresses already present on the network).

Building and executing the demo application

1. Open FreeRTOS/Demo/CORTEX_LPC1768_GCC_Rowley from within the CrossStudio IDE.

2. Connect the MCB1700 to the host computer using your choice of debug interface - then connect to the target by selecting "Connect" from the "Target" menu.

3. Select "Build and Debug" from the "Build" menu - the demo application should build with no errors or warnings before being programmed into the microcontroller Flash memory. The debugger will break on entry to main().

Functionality

The demo application creates 36 tasks before starting the scheduler. The tasks consist mainly of the standard demo tasks (see the demo application section for details of the individual tasks). Their only purpose is to test the kernel port and provide a demonstration of how to use the various API functions.

The following tasks and tests are created in addition to the standard demo tasks:

• Check function - called from the tick hook

  This only executes every five seconds. Its main function is to check that all the standard demo tasks are still operational. The check function maintains a status string that can be viewed on the "Task Stats" page served by the uIP TCP/IP web server.

• uIP task

  This is the task that handles the uIP stack. All TCP/IP processing is performed in this task.

• USB task

  This is the task that handles the USB stack. The USB device will enumerate as a CDC device. The USB task simply echoes received characters with an offset which by default is one. Therefore if 'A' is received 'B' will be echoed back. If 'x' is received 'y' will be echoed back, etc.

When executing correctly the demo application will behave as follows:

• LEDs P2.2, P2.3 and P2.4 are under the control of the standard 'flash' tasks. Each will toggle at a different but fixed frequency.

• The USB device port of the MCB1700 will enumerate as a CDC class device. To use the USB port (assuming a Windows host computer):
  1. Connect the MCB1700 to your host computer using the USB device port of the MCB1768 (ensuring the jumpers are set correctly for device operation).
  2. The host computer should recognise the new USB connection and prompt for the location of a suitable .inf file. Select the option to manually select the .inf file location, then browse to usbser.inf which is located in the FreeRTOS/Demo/CORTEX_LPC1768_GCC_Rowley directory. Assuming usbser.sys is available on your host computer the CDC device will be assigned a COM port number. The Windows Device Manager can be used to ascertain the actual number assigned.
  3. Open up a dumb terminal such as Hyperterminal and select the enumerated COM port number. Other parameters such as baud rate and flow control settings are not required and can be left at their default values.
  4. Type 'A' into the terminal window, if everything is working correctly you should see 'B' echoed back.

  Note that a queue is used to pass each individual character between the USB interrupt service routine and the USB task. This is a convenient method for a slow echo server, but very inefficient if large amounts of data are to be transferred.

• The target hardware will serve the web pages described below to a standard web browser. To connect to the target:
  1. Open a web browser on the connected computer.
  2. Type "HTTP://" followed by the target IP address into the browsers address bar.
     
     Entering the IP address into the web browser
     (obviously use the correct IP address for your system)

Note that the LCD is not used because the LCD driver is only permitted to be used with the Keil compiler.

Served Web Pages

The top of each served page includes a menu containing a link to every other page.

The served RTOS stats page showing status information on each task in the system.

The served run time stats page showing the processor utilisation of each task.

The served IO page

The IO page provides a simple interface that permits data to be sent to an LED. The check box permits the state of the user LED to be both set and queried. Changes are sent to the target hardware by clicking the "Update IO" button.

The TCP Stats and Connections pages display run time networking information.

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RTOS Configuration and Usage Details

RTOS Port specific configuration

Configuration items specific to these demos are contained in FreeRTOS/Demo/CORTEX_LPC1768_GCC_Rowley/FreeRTOSConfig.h. The constants defined in this file can be edited to suit your application. In particular -

• configTICK_RATE_HZ

  This sets the frequency of the RTOS tick. The supplied value of 1000Hz is useful for testing the kernel functionality but is faster than most applications require. Lowering this value will improve efficiency.

• configKERNEL_INTERRUPT_PRIORITY and configMAX_SYSCALL_INTERRUPT_PRIORITY

  See the kernel configuration documentation for full information on these configuration constants.

Attention please!: Remember that Cortex M3 cores use numerically low priority numbers to represent HIGH priority interrupts, which can seem counter-intuitive and is easy to forget! If you wish to assign an interrupt a low priority do NOT assign it a priority of 0 (or other low numeric value) as this can result in the interrupt actually having the highest priority in the system - and therefore potentially make your system crash if this priority is above configMAX_SYSCALL_INTERRUPT_PRIORITY.

The lowest priority on a Cortex M3 core is in fact 255 - however different Cortex M3 vendors implement a different number of priority bits and supply library functions that expect priorities to be specified in different ways. Use the supplied examples as a reference.

Each port #defines 'portBASE_TYPE' to equal the most efficient data type for that processor. This port defines portBASE_TYPE to be of type long.

Note that vPortEndScheduler() has not been implemented.

Interrupt service routines

In the demo application the vector table remains in flash.

Unlike most ports, interrupt service routines that cause a context switch have no special requirements and can be written as per the compiler documentation. The macro portEND_SWITCHING_ISR() can be used to request a context switch from within an ISR. An example interrupt service routine called vEMAC_ISR() is provided in FreeRTOS/Demo/CORTEX_LPC1768_GCC_Rowley/webserver/emac.c. This should be used as a reference example.

Note that portEND_SWITCHING_ISR() will leave interrupts enabled.

Switching between the pre-emptive and co-operative real time kernels

Set the definition configUSE_PREEMPTION within FreeRTOS/Demo/CORTEX_LPC1768_GCC_Rowley/FreeRTOSConfig.h to 1 to use pre-emption or 0 to use co-operative.

Compiler options

As with all the ports, it is essential that the correct compiler options are used. The best way to ensure this is to base your application on the provided demo application files.

Memory allocation

Source/Portable/MemMang/heap_2.c is included in the ARM Cortex-M3 demo application project to provide the memory allocation required by the real time kernel. Please refer to the Memory Management section of the API documentation for full information.

Copyright (C) 2004-2010 Richard Barry. Copyright (C) 2010-2012 Real Time Engineers Ltd.
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