RTOS Threads Analysis

Memfault automatically detects what RTOS your system is running. For uploaded coredumps, it will attempt to extract backtraces for all threads in the system and optionally determine what state each thread is in and the stack usage high water mark.

In order for this to work correctly, the coredump must capture the RTOS' thread state variables, all thread control blocks as well as the stack memory of each thread. The following sections list for each RTOS what needs to be captured. See the documentation on Coredump Collection for details on how to set up additional coredump capturing regions.

FreeRTOS

Required

These variables must be captured in the coredump. On top of this, the memory of all task control blocks (TCB_t) must be captured. Because FreeRTOS TCBs double as linked list nodes, all TCBs must be captured.

• uxCurrentNumberOfTasks
• pxCurrentTCB
• pxReadyTasksLists
• xDelayedTaskList1
• xDelayedTaskList2
• xPendingReadyList
• uxTopReadyPriority
• xSchedulerRunning

note

There were several releases of FreeRTOS that did not include uxTopUsedPriority, see this GitHub issue:

https://github.com/FreeRTOS/FreeRTOS-Kernel/issues/33#issue-583304006

If the version of FreeRTOS in use doesn't include the fix, add the sample file (for example, this copy) and relevant linker flags.

Optional

• xTasksWaitingTermination
• xSuspendedTaskList

To enable stack usage high water marking, the configCHECK_FOR_STACK_OVERFLOW configuration option must be enabled and the full stacks for each thread must be captured as well.

How to Capture the Required Variables

The memfault_freertos_ram_regions.c file contains details on selectively capturing the required variables.

note

Note that this is only necessary if all of RAM is not captured as part of the coredump (i.e. when coredump storage and bandwidth is limited).

The strategy has 2 parts:

1. update linker script to enclose the needed variables in a known region
2. update memfault_platform_coredump_get_regions() to include that region's data in a coredump region

See example implementations below.

GCC

Update the linker script (typically a file that ends with the .ld extension) to enclose the necessary .bss symbols with some exported symbols:

.bss (NOLOAD) :
{
    _sbss = . ;
    __bss_start__ = _sbss;
    __memfault_capture_bss_start = .;
    /* Place all objects from the FreeRTOS timers and tasks modules here.
       Note that some build systems will use 'timers.o' as the object
       file name, and some may use variations of 'timers.c.o' or
       'timers.obj' etc. This pattern should capture all of them. */
     *tasks*.o*(.bss COMMON .bss*)
     *timers*.o*(.bss COMMON .bss*)
    __memfault_capture_bss_end = .;

And then update memfault_platform_coredump_get_regions() to include those variables:

const sMfltCoredumpRegion *memfault_platform_coredump_get_regions(
    const sCoredumpCrashInfo *crash_info, size_t *num_regions) {
  int region_idx = 0;

  // any higher priority regions would go here, i.e. active stack

  // collect the FreeRTOS timer and task variables required for RTOS decode
  extern uint32_t __memfault_capture_bss_start;
  extern uint32_t __memfault_capture_bss_end;
  const size_t memfault_region_size = (uint32_t)&__memfault_capture_bss_end -
      (uint32_t)&__memfault_capture_bss_start;

  s_coredump_regions[region_idx] = MEMFAULT_COREDUMP_MEMORY_REGION_INIT(
    &__memfault_capture_bss_start, memfault_region_size);
  region_idx++;

  // remaining regions would go here. typically the
  // 'memfault_freertos_get_task_regions()' helper would be used to capture the
  // task data.
  region_idx += memfault_freertos_get_task_regions(&s_coredump_regions[region_idx],
      MEMFAULT_ARRAY_SIZE(s_coredump_regions) - region_idx);
  // remaining regions

IAR

Update the linker script (typically a file with a .icf extension) to include this line:

define block memfault_freertos { section .bss* object *tasks*.o*, section .bss* object *timers*.o* };

And then update memfault_platform_coredump_get_regions() to include that block:

// In the source file where memfault_platform_coredump_get_regions is defined add the following snippet
// Be sure to include additional sMfltCoredumpRegion entries in your regions array for the FreeRTOS regions
// created by the linker script and helper function
const sMfltCoredumpRegion *memfault_platform_coredump_get_regions(
    const sCoredumpCrashInfo *crash_info, size_t *num_regions) {
  int region_idx = 0;

  // any higher priority regions would go here, i.e. active stack

  // collect the block defined in the linker script
  const void *memfault_freertos_region_start = __section_start("memfault_freertos");
  const size_t memfault_freertos_region_size = __section_size("memfault_freertos");
  s_coredump_regions[region_idx] = MEMFAULT_COREDUMP_MEMORY_REGION_INIT(
     memfault_freertos_region_start, memfault_freertos_region_size);
  region_idx++;

  // remaining regions would go here. typically the
  // 'memfault_freertos_get_task_regions()' helper would be used to capture the
  // task data.
  region_idx += memfault_freertos_get_task_regions(&s_coredump_regions[region_idx],
      MEMFAULT_ARRAY_SIZE(s_coredump_regions) - region_idx);
  // remaining regions

Built-in FreeRTOS Metrics

The Memfault SDK has support for some built-in FreeRTOS Metrics:

• idle_task_run_time_percent (for both single- and dual-core systems)
• timer_task_stack_free_bytes

To enable these metrics, include the definition in the user heartbeat configuration file:

memfault_metrics_heartbeat_config.def

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Be sure to add the Memfault FreeRTOS Port files to your project, located here in the SDK: sdk/embedded/ports/freertos/src/

Zephyr

Required

These variables must be captured in the coredump:

• _kernel
• _kernel_openocd_offsets
• _kernel_openocd_size_t_size

Azure RTOS ThreadX

Required

These variables must be captured in the coredump:

• _tx_thread_current_ptr
• _tx_thread_created_ptr
• _tx_thread_created_count
• _tx_thread_system_state

Other RTOSs

Memfault also supports these other RTOSs: Argon, ChibiOS, Mynewt, NuttX, Quantum Platform, and Keil RTX5 / ARM mbedOS.