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Kinetis K60 ARM Cortex-M4 Demo
The official FreeRTOS zip file download contains source code for all the FreeRTOS ports, and every demo application project. It therefore contains many more files than are required to build and run the Kinetis K60 demo. See the Source Code Organization section for a description of the downloaded files, and information on creating a new project.
This is a very simple configuration. It creates two tasks,
one software timer, and also uses a button interrupt.
The two tasks communicate via a queue. The receiving task toggles the blue LED each time a value is received.
Pressing user button SW2 generates an interrupt. The interrupt service routine for which resets a software timer, then turns the green LED on. The software timer has a five second period. The timer will expire when SW2 has not been pressed again for a full five seconds. The callback function that executes when the timer expires simply turns the green LED off again. Therefore, pressing SW2 will turn the LED on, and the LED will remain on until a full five seconds pass without the button being pressed again.
The Blinky build configuration uses the main-blinky.c source file. The Full build configuration uses the main-full.c source file.
This is a comprehensive configuration that creates lots of tasks,
queues, semaphores (of various types) and software timers.
The Full configuration creates the same tasks and timers that are created by the Blinky build configuration (although different LEDs are used). In addition to these, the Full configuration also creates a lot of tasks from the set of standard demo tasks, and a simple web server task.
The standard demo tasks don't perform any particular function. Their purpose is firstly to test the FreeRTOS port, and secondly to provide examples of how to use the FreeRTOS API functions.
The Full build configuration creates yet more timers that are neither part of the Blinky configuration, or the set of standard demo tasks. These additional tasks are described briefly below this table.
In total, the Full configuration creates nearly 40 tasks! Use the blinky build configuration if a simpler demo is required to get started with.
Software timers that are created by the Full build configuration, that are not part of either the Blinky demo, or the standard demo tasks, include:
The check timer period is initially set to three seconds. The check timer callback function checks that all the standard demo tasks are not only still executing, but are executing without reporting any errors. If the check timer discovers that a task has either stalled, or reported an error, then it changes its own period from the initial three seconds, to just 200ms.
The check timer callback function also toggles the orange/red LED each time it is called. This provides a visual indication of the system status: If the LED toggles every three seconds, then no issues have been discovered. If the LED toggles every 200ms, then an issue has been discovered with at least one task.
The last reported issue is latched into the pcStatusMessage variable, and displayed at the bottom of the "task stats" web page served by the embedded web server task.
All the simple LED flash timers do is toggle an LED each when the timer callback function is executed. The two timers share a callback function, so the callback function parameter is used to determine which timer actually expired, and therefore, which LED to toggle. Both timers use a different frequency, one toggles the blue LED and the other the green LED.
This is the task that runs the uIP TCP/IP stack. All network related processing is performed in this task, making the TCP/IP Flash and RAM footprint extremely small compared to other embedded TCP/IP implementations. The served web pages are demonstrated further down this documentation page.
Hardware set up
All demo functionality, with the exception of the web server, will run on a TWR-K60N512
tower processor module, in its default configuration. J6 must be across pins 2 and 3
if the TWR-K60N512 is used without the rest of the tower kit.
The demo was created and tested using a J-Link to both debug and power the module. Powering the module from a J-Link requires jumper J12 to be fitted. With this configuration, terminal IO (printf()) is sent to the terminal IO window inside the IAR Embedded Workbench IDE.
To use the web server, the TWR-SER module is also required, and both the TWR-SER and TWR-K60N512 modules require jumpers moving from their default positions. The jumper changes are required because the demo is configured to communicate with the PHY using RMII mode - which in turn necessitates that the clock routed to the PHY remains synchronised with that routed to the K60. The required jumper positions are shown in the table below. Incorrect jumper positions can cause the network functionality to be slow and erratic.
|TWR-K60N512||J6||Across pins 2 and 3|
|TWR-SER||J2||Accross pins 3 and 4|
|TWR-SER||J3||Accross pins 2 and 3|
|TWR-SER||J12||Across pins 9 and 10 only (only one jumper fitted).|
Web server configuration
The IP address used by the microcontroller board is set by the constants
configIP_ADDR0 to configIP_ADDR3. These are specified at the bottom of the
FreeRTOSConfig.h header file that is located in the project directory. Constants
that define the MAC address and the NET mask are located in the same place of
the same file.
The IP addresses used by the web browser and the Kinetis K60 development board must be compatible. This can be ensured by making the first three octets of both IP addresses the same. For example, if the web browser computer uses IP address 192.168.0.1, then the Kinetis K60 development board can be given any address in the range 192.168.0.2 to 192.168.0.254 (other than any addresses that already exist on the same network).
The MAC address assigned to the Kinetis K60 must be unique on the network to which it is being attached.
The web server demo was developed and tested using a point to point (cross over) cable. A standard Ethernet cable may also be suitable - but is untested.
Using the web server
The top of each served page includes a menu with links to every other page.
The served run time stats page - showing
how much CPU time each task has consumed
The served IO page used to turn an LED
on and off using a CGI script.
The IO page provides a simple interface to permit the yellow LED to be turned on and off from a web browser. Changes are sent to the target board whenever the "Update IO" button is clicked, or the page is refreshed.
Other served pages include TCP/IP statistics and a large JPG image. All the web pages are included in the downloaded binary image - which can make the binary image appear to be quite large (the jpg file by itself is in excess of 36K).
Cortex-M FreeRTOS port specific configuration
Configuration items specific to this demo are contained in FreeRTOS/Demo/CORTEX_Kinetis_K60_Tower_IAR/FreeRTOSConfig.h.
The constants defined in this file can be edited to suit your application. In particular -
This sets the frequency of the RTOS tick interrupt. The supplied value of 1000Hz is useful for testing the RTOS kernel functionality but is faster than most applications require. Lowering this value will improve efficiency.
See the RTOS kernel configuration documentation for full information on these configuration constants.
These are equivalents to configKERNEL_INTERRUPT_PRIORITY and configMAX_SYSCALL_INTERRUPT_PRIORITY, but presented in a form suitable for passing into the Freescale set_irq_priority() library function. The set_irq_priority() function expects priorities to be in the range of 0 to 15 - 0 being the highest priority and 15 being the lowest priority.
Interrupt safe FreeRTOS API functions must not be called from an interrupt that has a priority above that defined by configLIBRARY_MAX_SYSCALL_INTERRUPT_PRIORITY. Doing so will make your application unstable. This is the most common error when using FreeRTOS on ARM Cortex-M devices!
Attention please!: See the page dedicated to setting interrupt priorities on ARM Cortex-M devices. Remember that ARM Cortex-M cores use numerically low priority numbers to represent HIGH priority interrupts. This 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 will 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. Also, do not leave interrupt priorities unassigned, as by default they will have a priority of 0 and therefore the highest priority possible.
The lowest priority on a ARM Cortex-M core is in fact 255 - however different Cortex-M vendors implement a different number of priority bits and supply library functions that expect priorities to be specified in different ways. For example, on Kinetis microcontrollers, the lowest priority you can specify is in fact 15 - this is defined by the constant configLIBRARY_LOWEST_INTERRUPT_PRIORITY in FreeRTOSConfig.h. The highest priority that can be assigned is always zero.
It is also recommended to ensure that all four priority bits are assigned as being premption priority bits, and none as sub priority bits.
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.
Interrupt service routines
In this demo, interrupts are installed into the vector table inside the vectors.h
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 interrupt service routine.
Note that portEND_SWITCHING_ISR() will leave interrupts enabled.
This demo project provides examples of FreeRTOS interrupt service routines - namely vPort_E_ISRHandler() defined in main-full.c and main-blinky.c, and the three Ethernet interrupt handlers vEMAC_TxISRHandler(), vEMAC_RxISRHandler and vEMAC_ErrorISRHandler() defined in emac.c.
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_SYSCALL_INTERRUPT_PRIORITY configuration constant.
Resources used by FreeRTOS
FreeRTOS requires exclusive use of the SysTick and PendSV interrupts. SVC number #0 is also used.
Source/Portable/MemMang/heap_2.c is included in the K60 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