Philips (now NXP Semiconductors) LPC2129 (ARM7) RTOS Port
for the IAR Development Tools
[RTOS Ports]

There are currently four FreeRTOS ports for the Philips LPC2000 ARM7 based embedded microcontroller. This page relates only to the port for the IAR development tools.

The port was developed on an MCB2100 development/prototyping board using a J-LINK USB JTAG interface (instructions are provided should you wish to use an alternative development board).

The MCB2100 is a fully featured and comprehensive prototyping board that allows easy access to the LPC2129 peripherals and includes 8 built in LEDs which are utilised by the FreeRTOS demo application.

Note: If this project fails to build then it is likely the version of IAR Embedded Workbench being used is too old. If this is the case, then it is also likely that the project file has been (silently) corrupted and will need to be restored to its original state before it can be built even with an updated IAR version.

IMPORTANT! Notes on using the IAR LPC2000 RTOS port

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

Source Code Organisation

The IAR Embedded Workbench project file for this demo can be found in the Demo/ARM7_LPC2129_IAR directory, which also contains main.c, the source file containing the main() function.

The Demo/ARM7_LPC2129_IAR/SrcIAR and the Demo/ARM7_LPC2129_IAR/resource directories contain support files for the IAR Philips build environment.

The Demo Application

Functionality

Two configurations are provided within the project file - 'flash debug' with no optimisation, and 'flash bin' will full optimisation (barring the static clustering option).

The demo application creates 25 of the standard demo tasks, the idle task, and a 'Check' task. See the demo application section for details of the individual tasks. When executing correctly the demo application will behave as follows:

• LEDs P1.16, P1.17 and P1.18 are under control of the 'flash' tasks. Each will flash at a constant frequency, with LED P1.16 being the slowest and LED P1.18 being the fastest.

• LED P1.19 will flash each time a character is transmitted on the serial port.

• LED P1.20 will flash each time a character is received on the serial port.

• Not all the tasks update an LED so have no visible indication that they are operating correctly. Therefore a 'Check' task is created whose job it is to ensure that no errors have been detected in any of the other tasks.

  LED P1.23 is under control of the 'Check' task. Every three seconds the 'Check' task examines all the tasks in the system to ensure they are executing without error. It then toggles LED P1.23. If LED P1.23 is toggling every three seconds then no errors have ever been detected. The toggle rate increasing to 500ms indicates that the 'Check' task has discovered at least one error. This mechanism can be checked by removing the loopback connector from the serial port (described below), and in doing so deliberately generating an error.

Demo application hardware setup

The demo application uses the LEDs built into the prototyping board so no other hardware setup is required.

Building the demo application

Selecting the 'Flash Debug' configuration

Running the demo application

1. Ensure the J-Link JTAG debug interface is connected and that the prototype board is power up.
2. Select 'Debug' from the IDE 'Project' menu.
3. The microcontroller Flash memory will automatically get programmed with the demo application, and if using the debug build the debugger will break at main(). Select 'Go' from the IDE 'Debug' menu to start the application executing.

An alternative JTAG interface can be selected using the Debugger category within the project options dialogue box.

Configuration and Usage Details

RTOS port specific configuration

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

Note that vPortEndScheduler() has not been implemented.

Interrupt service routines

    static __arm __irq void vAnISR( void )
    {
        /* ISR C code goes here. */

        /* End the interrupt in the VIC. */
        VICVectAddr = 0;
    }

Often you will require an interrupt service routine to cause a context switch. For example a serial port character being received may wake a high priority task that was blocked waiting for the character. If the ISR interrupted a lower priority task then it should return immediately to the woken task. Limitations in the IAR inline assembler necessitate such interrupt service routines include an assembly file wrapper.

An example of an ISR with context switching capabilities

    /* For simplicity the C function should operate in ARM mode.
       Note that the __irq modifier is NOT used. */

    __arm void vASwitchingISR( void )
    {
        char cContextSwitchRequired;

        /* Write the ISR body here as per normal.

        A boolean is used to say whether a context switch is required.
        In this example assume we posted onto a queue and this caused a
        task to be woken. */

        cContextSwitchRequired = pdTRUE;

        /* Immediately before the end of the ISR call the
        portEND_SWITCHING_ISR() macro. */

        portEND_SWITCHING_ISR( ( cContextSwitchRequired ) );

        /* End the interrupt in the VIC. */
        VICVectAddr = 0;
    }

The entry point for the ISR has to be written in an assembly file. This just places a call to the C function between calls to the portSAVE_CONTEXT() and portRESTORE_CONTEXT() macros respectively as per the following template:

        EXTERN vASwitchingISR
        PUBLIC vASwitchingISREntry

    /* This header defines the save/restore macros. */
    #include "ISR_Support.h"

    vASwitchingISREntry:

        portSAVE_CONTEXT      ; Call portSAVE_CONTEXT macro first
        bl  vASwitchingISR    ; Then call the function written in the C file.
        portRESTORE_CONTEXT   ; Call portRESTORE_CONTEXT last.

        END

To use a part other than an LPC2129

• prvSetupTimerInterrupt() in Source/portable/IAR/LPC2000/port.c configures the LPC2129 timer 0 to generate the RTOS tick.
• Port, memory access and system clock configuration is performed by prvSetupHardware() within Demo/ARM7_LPC2129_IAR/main.c.
• The interrupt service routine setup and management assume the existence of the vectored interrupt controller.
• The serial port drivers.
• Register location definitions are provided the file iolpc2129.h which is included at the top of Demo/ARM7_LPC2129_IAR/FreeRTOSConfig.h.
• Startup code is contained within Demo/ARM7_LPC2129_IAR/SrcIAR/cstartup.s79. main() must be called with the processor in Supervisor mode.
• RAM size - see Memory Allocation below.

Switching between the pre-emptive and co-operative RTOS kernels

Compiler options

Execution Context

NOTE! : The processor MUST be in supervisor mode when the RTOS scheduler is started (vTaskStartScheduler is called). The demo applications included in the FreeRTOS download switch to supervisor mode prior to main being called. If you are not using one of these demo application projects then ensure Supervisor mode is entered before calling vTaskStartScheduler().

Interrupt service routines always run in ARM mode. All other code will run in either ARM or THUMB mode depending on the build. It should be noted that some of the macros defined in portmacro.h can only be called from ARM mode code, and use from THUMB code will result in a compile time error. The Embedded Workbench project is configured for THUMB mode - see the LPC2006 GCC port for an example of the configuration required to use just ARM mode.

Demo/ARM7_LPC2129_IAR/Startup.s configures stacks for system/user, IRQ and SWI modes only.

SWI instructions are used by the real time kernel and can therefore not be used by the application code.

Memory allocation

Serial port driver