9.7. SafeRTOS Usage and Migration Guidelines

This section provides information on migrating to SafeRTOS from FreeRTOS on PDK.

9.7.1. Overview of SafeRTOS

SafeRTOS is a functional safety, pre-certified, Real Time Operating System (RTOS) for embedded processors. It is a derivative of FreeRTOS. SafeRTOS is developped by WITTENSTEIN high integrity systems (WHIS) ®. SafeRTOS is based on the functional model of FreeRTOS, however, it is not the FreeRTOS kernel, and therefore, migration to SaferRTOS from FreeRTOS should be thought of as integrating a whole new RTOS.

9.7.2. SafeRTOS and the OS Abstraction Layer

SDK had already taken care of SafeRTOS recommendations when using SafeRTOS APIs. All drivers in the SDK are OS agnostic with the usage of OSAL APIs. This make sure TI drivers and SW built on top of FreeRTOS can be reused with SafeRTOS.

The Processor SDK provides an Operating System Abstraction Layer(OSAL). OSAL tries to take in all the OS specific function calls and provides a uniform view to the application. For the migration from FreeRTOS to SafeRTOS, OSAL takes in all the required changes. If OSAL is not used by the application, then the application needs to take care of the required changes for the migration to SafeRTOS. IF not using the OSAL, then please refer the WHIS documentation on FreeRTOS to SafeRTOS migration which can be found here: <SAFERTOS_INSTALL_DIR>/Documentation/Manuals/`Upgrading from FreeRTOS to SafeRTOS.pdf`.

Following sections discuss about key care-abouts when migrating from FreeRTOS to SafeRTOS in Processor SDK using the OSAL.

9.7.3. SafeRTOS migration from FreeRTOS

Changes in R5 Applications due to SafeRTOS migration

  • SafeRTOS provides Freedom From Interferance(FFI), by virtue of which tasks can be created in User Mode, or in Privileged Mode. Also, two task specific MPU regions can also be provided.
  • To provide FFI support, SafeRTOS owns the MPU configuration.

  • This means, the application needs to use SafeRTOS APIs to configure various MPU regions.

  • For programming the MPU regions in FreeRTOS, CSL structure, `CSL_ArmR5MpuRegionCfg` was used, which the applications could override and provide their own configurations.

    • OSAL SafeRTOS provides a structure implementation for configuring the MPU regions that is very similar to the CSL counterpart in FreeRTOS: `xMPU_CONFIG_PARAMETERS`. The default MPU configurations is defined in `gMPUConfigParms`, which is weakly defined here: <SDK_INSTALL_DIR>/pdk/packages/ti/osal/src/safertos/SafeRTOS_mpu_r5f.c. This definition of the MPU table can also be overriden by the application.
  • SafeRTOS applications have only 9 programmable MPU regions as opposed to 16 configurable MPU regions in FreeRTOS.
  • SafeRTOS reserves MPU configurations for the following:
  • 1 Global region.
  • 3 Kernel specific regions.
  • 1 Task stack region.
  • 2 Task specific regions.
  • The task stack needs to be an entry in the MPU configuration table. This mandates the task stack to be aligned with the stack size.
  • To enable CCS debugging, user needs to set permission for the portmpuREGION_SYS_CONFIGURATION to READ_WRITE in the <SAFERTOS_INSTALL_DIR>/source_code_and_projects/SafeRTOS/portable/199_TI_CR5/portmpu.h Refer WHIS Documentation at <SAFERTOS_VERSION> EVAL - TI CLANG <BOARD>-<ISA> readme.rtf in <SAFERTOS_INSTALL_DIR> for more details.

Common changes due to SafeRTOS migration

  • For all the cores, the linker command files need to take care of the additional sections that SafeRTOS requires.
    • The common linker files can be found in <PSDK_RTOS>/pdk/packages/ti/build/<SOC>/linker_<ISA>_safertos.<cmd or lds>.
    • User can refer this linker file as a reference for creating new linker command files.
    • The SafeRTOS demo linker file can also be referred which can be found in: <SAFERTOS_INSTALL_DIR>/source_code_and_projects/demo_projects/SafeRTOS_<BOARD>_<ISA>_Demo/linker_core_<ISA>.lds

9.7.3.1. Limitations

  • OSAL FreeRTOS had an implemention for the LoadP API, which calculates the CPU and Task load. For SafeRTOS this implementation is not provided in the OSAL.
    • For Load measurements / run-time stats, please refer WHIS SafeRTOS User Guide, or contact WHIS.
  • CCS ROV is not supported for SafeRTOS.
    • SafeRTOS debug awareness is supported in Lauterbach.