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Xilinx Zynq-7000 (dual core ARM Cortex-A9) SoC Port
Demonstrated on a ZC702 evaluation kit
[RTOS Ports]

This page documents a FreeRTOS demo application for the Xilinx Zynq-7000 SoC, which incorporates a dual core ARM Cortex-A9 processor.

The demo is pre-configured to build with the Xilinx SDK tools (version 2016.1 at the time of writing) and execute on the ZC702 evaluation board.

The project uses the default hardware design and board support package (BSP) shipped with the SDK, and builds FreeRTOS and lwIP as part of the application (rather than part of the BSP).

IMPORTANT! Notes on using the FreeRTOS ARM Cortex-A9 port on the Xilinx Zynq-7000 SoC

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

  1. Source Code Organisation
  2. The Demo Application Functionality
  3. Build Instructions
  4. RTOS Configuration and Usage Details
Also see the FAQ My application does not run, what could be wrong?, and the page that provides instruction on using FreeRTOS on ARM Cortex-A embedded processors.

Source Code Organization

The FreeRTOS download contains the source code for all the FreeRTOS ports, and every demo application. That means it contains many more files than are required to use the Zynq port, or the official Zynq demo application. See the Source Code Organization section of this web site for a description of the downloaded files, and information on creating a new project.

The directory structure used by the demo application is shown and described below. The root CORTEX_A9_Zynq_ZC702 directory is itself located in FreeRTOS/Demo.

    +-RTOSDemo           Contains the SDK project and C files specific to the demo.
    +-RTOSDemo_bsp       Contains the hardware BSP.
    +-ZC702_hw_platform  The hardware description.

Notes relating to the directory structure:
  • The projects contained in the ZC702_hw_platform and RTOSDemo_bsp directories are the defaults generated by the SDK when the ZC702 is selected as the target hardware for a new project.

  • The RTOSDemo directory only contains the source files that are specific to the Zynq demo. The FreeRTOS source files, and the source files that implement tasks that are common to all demo applications, are located elsewhere in the directory tree. Therefore the project will only build when the default directory structure is unchanged. Also see the page that describes how to use virtual and linked paths in the Eclipse project explorer.

The Zynq-7000 SoC Demo Application


The constant mainSELECTED_APPLICATION, which is #defined at the top of main.c, is used to switch between a simply Blinky style demo, a more comprehensive test and demo application, and an lwIP demo, as described in the next two sections.

Functionality with mainSELECTED_APPLICATION set to 0

If mainSELECTED_APPLICATION is set to 0 then main() will call main_blinky(), which is implemented in main_blinky.c.

main_blinky() creates a very simple demo that includes two tasks and one queue. One task repeatedly sends the value 100 to the other task through the queue. The receiving task toggles an LED each time it receives the message. The message is sent every 200 milliseconds, so the LED toggles every 200 milliseconds.

Functionality with mainSELECTED_APPLICATION set to 1

If mainSELECTED_APPLICATION is set to 1 then main() will call main_full(), which is implemented in main_full.c.

FreeRTOS on ARM Cortex-A9 main_full() creates a comprehensive test and demo application that demonstrates:

Connect to FreeRTOS+CLI though the USB to UART bridge USB mini connector using 115200 baud. Type 'help' in the CLI to see a list of the registered commands.

Most of the tasks created by the demo are from the set of standard demo tasks. These are used by all FreeRTOS demo applications, and have no specific functionality or purpose other than to demonstrate the FreeRTOS API being used and test the RTOS kernel port.

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

  • Register test tasks

    These two tasks test the RTOS kernel context switch mechanism by first filling each Cortex-A9 register (including the floating point registers) with a known and unique value, then repeatedly checking that the value originally written to the register is maintained in the register, for the lifetime of the task. The tasks execute at the lowest possible priority (the idle priority), so are preempted frequently. The nature of these tasks necessitates that they are written in assembly.

  • Interrupt nesting test tasks

    Two timers are used to test FreeRTOS queues being used from interrupts that nest to a depth of 3 (including the RTOS tick interrupt). A third timer is configured to generate a 20KHz interrupt at a priority above the maximum system call interrupt priority (the maximum system call interrupt priority is explained on the "Running FreeRTOS on a Cortex-A9" page) - giving a total tested interrupt nesting depth of 4.

    The high frequency timer is also used as a convenient time source for the collection of run-time statistics. The collected statistics can be viewed using the CLI.

  • A 'check' task

    The check task periodically queries the standard demo tasks and the register test tasks to ensure they are functioning as intended. The check task also toggles an LED to give a visual indication of the system status. If the LED toggles every 3 seconds then the check task has not discovered any problems with the executing demo. If the LED toggles every 200 milliseconds then the check task has discovered a problem in at least one task..

Functionality with mainSELECTED_APPLICATION set to 2

If mainSELECTED_APPLICATION is set to 2 then main() will call main_lwIP(), which is implemented in main_lwIP.c.

The lwIP example can be configured to use either a static or dynamic IP address:

  • To use a dynamically allocated IP address set LWIP_DHCP to 1 in lwipopts.h and connect the target to a network that includes a DHCP server. The obtained IP address is printed to the UART console.

  • To use a static IP address set LWIP_DHCP to 0 in lwipopts.h and set the static IP address using the configIP_ADDR0 to configIP_ADDR3 constants at the bottom of FreeRTOSConfig.h. Constants used to define a netmask are also located at the bottom of FreeRTOSConfig.h. The selected IP address and netmask must be compatible with the network to which the embedded target is to be connected. This can normally be achieved by setting the first three octects of the target's IP address and netmask to match the first three octects of the host computer's IP address and netmask respectively. The chosen IP address must be unique on the network.

A cross over (point to point) Ethernet cable must be used if the target and host systems are connected directly (without going through a hub or switch).

When connected correctly the demo uses the lwIP sockets API to create a FreeRTOS+CLI command console, and the lwIP raw API to create a basic HTTP web server. Server side includes (SSI) are used to generate dynamic data in the served web pages. To connect to the http server simply type the IP address of the target into the address bar of a web browser.

To connect to FreeRTOS+CLI, open a command prompt and enter "telnet <ipaddr>" where <ipaddr> is the IP address of the target. Once connected type "help" to see a list of registered commands. Note this example does not implement a real telnet server, it just uses the telnet port number to allow easy connection using telnet tools.

Hardware setup

The demo uses the default hardware configuration.

All of the 5-way boot selection switches must be switched to the right hand side when the board is viewed with the integrated Digilent JTAG module on the lower edge. This enables booting via JTAG.

Build Instructions

Importing the demo application project into the SDK Eclipse workspace

To import the Xilinx Software Development Kit (SDK) project into an existing or new Eclipse Workspace:

  1. Select "Import" from the SDK "File" menu. The dialogue box shown below will appear. Select General->Existing Project into Workspace, as shown in the image.

    Importing the Xilinx MicroBlaze RTOS demo project into the SDK
    The dialogue box that appears when "Import" is first clicked

  2. In the next dialogue box, select FreeRTOS/Demo/CORTEX_A9_Zynq_ZC702 as the root directory. Then, make sure the RTOSDemo, RTOSDemo_bsp and ZC702_hw_platform projects are checked in the "Projects" area, and that the Copy Projects Into Workspace box is not checked, before clicking the Finish button (see the image below for the correct check box states).

    Importing the free ARM Cortex-A9 RTOS Demo Source project into the Xilinx SDK
    Make sure all three projects are checked, and "Copy projects into workspace" is not checked

  3. Once all three projects have been imported, the project explorer window of the SDK IDE will appear as below.

    The ZC702_hw_platform and RTOSDemo_bsp projects are dependencies of the RTOSDemo project, so only the RTOSDemo project needs to be built explicitly.

    The Cortex-A9 RTOS projects viewed in the Eclipse project explorer.
    All three projects imported into the workspace

Building the demo application

  1. Open the project's main.c file, and set mainSELECTED_APPLICATION to generate the simple blinky demo, the full test and demo application, or the lwIP Ethernet example, as required.

  2. Select 'Rebuild All' from the IDE 'Project' menu. The application should build without any errors or warnings.

Note: At the time of writing there is a bug in the dependency management in the SDK. If a header file is edited then it is necessary to perform a complete clean and re-build of the entire project for the change to take effect. Failure to do this will result in seemingly inexplicable run-time behaviour.

Starting a debug session

  1. Ensure the ZC702 evaluation board is powered up and connected via its on-board Digilent JTAG port to the host computer.

  2. Select 'Debug Configurations...' from the IDE's 'Run' menu. The Debug Configurations dialogue box will appear. Double click 'Xilinx C/C++ application (System Debugger)' to create a new debug configuration.

  3. Configure the 'Target Setup' tab as shown in the image below.

    ARM Cortex-A9 target setup tab
    The required settings on the Target Setup tab

  4. Configure the 'Application' tab as shown in the image below.

    ARM Cortex-A9 RTOS application tab
    The required settings on the Application tab

    All the other tabs in the 'Debug Configurations' dialogue can be left with their default settings.

  5. Click the "Debug" button to commence debugging. The application will be downloaded to RAM and the debugger will break on entry to main().

RTOS Configuration and Usage Details

FreeRTOS ARM Cortex-A port specific configuration

Attention please!: Refer to the the page that provides instruction on using FreeRTOS on ARM Cortex-A embedded processors, paying particular attention to the value and meaning of the configMAX_API_CALL_INTERRUPT_PRIORITY setting, and the special notes regarding using the floating point unit with GCC.

Configuration items specific to this demo are contained in /FreeRTOS/Demo/CORTEX_A9_Zynq_ZC702/RTOSDemo/src/FreeRTOSConfig.h. The constants defined in this file can be edited to suit your application.

Interrupt vector table

By default, SDK projects define the interrupt vector table as part of the BSP. This makes it difficult to install the FreeRTOS handlers using the methods described on the page about running FreeRTOS on ARM Cortex-A embedded processors. Therefore this demo defines its own interrupt vector table in FreeRTOS_asm_vectors.S. The vector table defined by the BSP is replaced by the vector table defined in FreeRTOS_asm_vectors.S at run time by calling vPortInstallFreeRTOSVectorTable(), which in the demo, is done in the prvSetupHardware() function.

The vector table defined in FreeRTOS_asm_vectors.S is placed in a linker segment called .freertos_vectors, and the linker script lscript.ld places the .freertos_vectors segment at the beginning of the .text region.

[Application Defined] Interrupt service routines

This demo uses drivers provided by Xilinx to configure the interrupt controller, and install application defined interrupts. Examples can be found in FreeRTOS/Demo/CORTEX_A9_Zynq_ZC702/RTOSDemo/src/Full_Demo/serial.c and FreeRTOS/Demo/CORTEX_A9_Zynq_ZC702/RTOSDemo/src/Full_Demo/IntQueueTimer.c.

The Xilinx drivers require interrupt service routines (ISRs) to accept a void * parameter, although the parameter is not always used. The required ISR prototype is therefore:

    void Interrupt_Handler( void *pvUnusedParameter );
The interrupt handler called prvUART_Handler() in serial.c provides an example of an interrupt handler that does not use its parameter. The interrupt handler called prvTimerHandler() in IntQueueTimer.c provides an example of an interrupt that uses its parameter to determine which peripheral generated the interrupt, as in that case the same interrupt handler implementation is installed as the handler for more than one timer.

If an ISR causes a task of equal or higher priority than the currently executing task to leave the Blocked state then the ISR must request a context switch before the ISR exits. When this is done the interrupt will interrupt one RTOS task, but return to a different RTOS task.

The macros portYIELD_FROM_ISR() (or portEND_SWITCHING_ISR()) can be used to request a context switch from within an ISR. The following source code snippet is provided as an example. The example ISR uses a semaphore to synchronise with a task (not shown), and calls portYIELD_FROM_ISR() to ensure the interrupt returns directly to the task. The prvUART_Handler() and prvTimerhandler() functions already referenced provide further examples.

void Dummy_IRQHandler( void *pvUnusedInThisExample )
long lHigherPriorityTaskWoken = pdFALSE;

    /* The parameter is not used in this case. */
    ( void ) pvUnusedInThisExample;

    /* Clear the interrupt if necessary. */

    /* This interrupt does nothing more than demonstrate how to synchronise a
    task with an interrupt.  A semaphore is used for this purpose.  Note
    lHigherPriorityTaskWoken is initialised to pdFALSE. */
    xSemaphoreGiveFromISR( xTestSemaphore, &lHigherPriorityTaskWoken );

    /* If there was a task that was blocked on the semaphore, and giving the
    semaphore caused the task to unblock, and the unblocked task has a priority
    higher than or equal to the currently Running task (the task that this
    interrupt interrupted), then lHigherPriorityTaskWoken will have been set to
    pdTRUE internally within xSemaphoreGiveFromISR().  Passing pdTRUE into the
    portYIELD_FROM_ISR() macro will result in a context switch being pended to
    ensure this interrupt returns directly to the unblocked, higher priority,
    task.  Passing pdFALSE into portYIELD_FROM_ISR() has no effect. */
    portYIELD_FROM_ISR( lHigherPriorityTaskWoken );

Only FreeRTOS API functions that end in "FromISR" can be called from an interrupt service routine - and then only if the priority of the interrupt is less than or equal to that set by the configMAX_API_CALL_INTERRUPT_PRIORITY configuration constant (meaning a numerically higher value).

Resources used by FreeRTOS

Information is provided on the Using FreeRTOS on ARM Cortex-A Embedded Processors page. This demo is configured to generate the tick interrupt from the SCU timer.

Memory allocation

Source/Portable/MemMang/heap_4.c is included in the ARM Cortex-A demo application project to provide the memory allocation required by the RTOS kernel. Please refer to the Memory Management section of the API documentation for full information.


Note that vPortEndScheduler() has not been implemented.

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