The use of an ARM Cortex-M4 core in the new MSP432 microcontroller platform has brought the benefits of the huge, diverse and non-proprietary ARM ecosystem to MSP430 MCU users. One of the most popular components in that ecosystem is FreeRTOS – probably the most widely used and best-supported real time kernel [in its class] on the planet. Real Time Engineers Ltd. released a maintained FreeRTOS demo for MSP432 MCUs on the day TI’s new microcontroller platform was announced.
Figure 1 The FreeRTOS command line used in the FreeRTOS MSP432 demo
The FreeRTOS demo targets the MSP-EXP432P401R LaunchPad Development Kit, and pre-configured build projects are provided for both the IAR and Keil tools – two of the most popular mid-priced development environments for ARM microcontrollers. Also, and for the first time, there is now a FreeRTOS Cortex-M port for TI’s own ARM compiler, along with a maintained demo for Code Composer Studio (CCS) IDE that uses the new port. FreeRTOS’s GCC and Tasking compiler ports for the Cortex-M4F will also work with MSP432 MCUs, although no pre-configured MSP432 MCU examples are provided for those compilers yet.
Updated FreeRTOS demos have also been created for, and will be maintained for, MSP430FR5969 MCUs. At the time of writing, the MSP430FR5969 MCU demo is only available from FreeRTOS’s public SVN repository, but it will be included in the next official FreeRTOS release.
Figure 2 The FreeRTOS StateViewer plug-in shipped with the IAR IDE
For the power-consumption-conscious, FreeRTOS has long included an option for tick suppression through its tick-less idle mode. Tick-less idling allows the tick interrupt to be turned off only when it is pre-determined that no tasks are scheduled to run for a fixed and user-configurable time into the future – typically three to ten ticks into the future depending on the time and energy required to enter then exit a deep sleep mode. Turning the tick interrupt off only during idle periods removes the need for the next task execution time to be determined, and then the clock re-programmed appropriately, on each context switch – reducing the processing overhead and the length of each task switch. Pre and post sleep hook functions enable calls into application specific sleep management libraries in order to determine the sleep mode that should be entered, or even to abort entry into a sleep mode at altogether (note the initial FreeRTOS demo uses the generic Cortex-M tick-less mode, rather than an implementation tailored specifically to use the low power features of MSP432 MCUs).
FreeRTOS has become the globally successful de facto standard for microcontrollers by offering a truly compelling value proposition, with complete peace of mind; it is professionally developed, strictly quality controlled, robust, supported, independent, cross platform, and free to embed in commercial products without any requirement to expose your proprietary source code. It has also removed all the common objections to using free software in commercial applications, including the risk of accidental IP infringement. Even so, some companies still insist that somebody is accountable for all the software that is incorporated into their products, and for those customers a very low-cost commercial license for FreeRTOS may be purchased from our partner company. Commercially licensed versions of FreeRTOS are fully indemnified, and sold under the OpenRTOS brand.
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