Ewout van Bekkum | 749342b | 2021-01-19 14:53:19 -0800 | [diff] [blame] | 1 | .. _module-pw_thread_freertos: |
| 2 | |
Ewout van Bekkum | b9b1d36 | 2021-05-14 17:16:07 -0700 | [diff] [blame] | 3 | ================== |
Ewout van Bekkum | 749342b | 2021-01-19 14:53:19 -0800 | [diff] [blame] | 4 | pw_thread_freertos |
Ewout van Bekkum | b9b1d36 | 2021-05-14 17:16:07 -0700 | [diff] [blame] | 5 | ================== |
| 6 | This is a set of backends for pw_thread based on FreeRTOS. |
Ewout van Bekkum | 749342b | 2021-01-19 14:53:19 -0800 | [diff] [blame] | 7 | |
Ewout van Bekkum | b9b1d36 | 2021-05-14 17:16:07 -0700 | [diff] [blame] | 8 | .. contents:: |
| 9 | :local: |
| 10 | :depth: 1 |
| 11 | |
| 12 | .. Warning:: |
| 13 | This module is still under construction, the API is not yet stable. |
| 14 | |
| 15 | ----------------------- |
| 16 | Thread Creation Backend |
| 17 | ----------------------- |
| 18 | A backend for ``pw::thread::Thread`` is offered using ``xTaskCreateStatic()``. |
| 19 | Optional dynamic allocation for threads is supported using ``xTaskCreate()``. |
| 20 | Optional joining support is enabled via an ``StaticEventGroup_t`` in each |
| 21 | thread's context. |
| 22 | |
| 23 | This backend always permits users to start threads where static contexts are |
| 24 | passed in as an option. As a quick example, a detached thread can be created as |
| 25 | follows: |
| 26 | |
| 27 | .. code-block:: cpp |
| 28 | |
| 29 | #include "FreeRTOS.h" |
| 30 | #include "pw_thread/detached_thread.h" |
| 31 | #include "pw_thread_freertos/context.h" |
| 32 | #include "pw_thread_freertos/options.h" |
| 33 | |
| 34 | pw::thread::freertos::StaticContextWithStack<42> example_thread_context; |
| 35 | void StartExampleThread() { |
| 36 | pw::thread::DetachedThread( |
| 37 | pw::thread::freertos::Options() |
| 38 | .set_name("static_example_thread") |
| 39 | .set_priority(kFooPriority) |
| 40 | .set_static_context(example_thread_context), |
| 41 | example_thread_function) |
| 42 | } |
| 43 | |
| 44 | Alternatively when ``PW_THREAD_FREERTOS_CONFIG_DYNAMIC_ALLOCATION_ENABLED`` is |
| 45 | enabled, dynamic thread allocation can be used. The above example could instead |
| 46 | be done as follows: |
| 47 | |
| 48 | .. code-block:: cpp |
| 49 | |
| 50 | #include "FreeRTOS.h" |
| 51 | #include "pw_thread/detached_thread.h" |
| 52 | #include "pw_thread_freertos/context.h" |
| 53 | #include "pw_thread_freertos/options.h" |
| 54 | |
| 55 | void StartExampleThread() { |
| 56 | pw::thread::DetachedThread( |
| 57 | pw::thread::freertos::Options() |
| 58 | .set_name("dyanmic_example_thread") |
| 59 | .set_priority(kFooPriority) |
| 60 | .set_stack_size(42), |
| 61 | example_thread_function) |
| 62 | } |
| 63 | |
| 64 | |
| 65 | Module Configuration Options |
| 66 | ============================ |
| 67 | The following configurations can be adjusted via compile-time configuration of |
| 68 | this module, see the |
| 69 | :ref:`module documentation <module-structure-compile-time-configuration>` for |
| 70 | more details. |
| 71 | |
| 72 | .. c:macro:: PW_THREAD_FREERTOS_CONFIG_JOINING_ENABLED |
| 73 | |
| 74 | Whether thread joining is enabled. By default this is disabled. |
| 75 | |
| 76 | We suggest only enabling this when thread joining is required to minimize |
| 77 | the RAM and ROM cost of threads. |
| 78 | |
| 79 | Enabling this grows the RAM footprint of every ``pw::thread::Thread`` as it |
| 80 | adds a ``StaticEventGroup_t`` to every thread's |
| 81 | ``pw::thread::freertos::Context``. In addition, there is a minute ROM cost to |
| 82 | construct and destroy this added object. |
| 83 | |
| 84 | ``PW_THREAD_JOINING_ENABLED`` gets set to this value. |
| 85 | |
| 86 | .. c:macro:: PW_THREAD_FREERTOS_CONFIG_DYNAMIC_ALLOCATION_ENABLED |
| 87 | |
| 88 | Whether dynamic allocation for threads (stacks and contexts) is enabled. By |
| 89 | default this matches the FreeRTOS configuration on whether dynamic |
| 90 | allocations are enabled. Note that static contexts **must** be provided if |
| 91 | dynamic allocations are disabled. |
| 92 | |
| 93 | .. c:macro:: PW_THREAD_FREERTOS_CONFIG_DEFAULT_STACK_SIZE_WORDS |
| 94 | |
| 95 | The default stack size in words. By default this uses the minimal FreeRTOS |
| 96 | stack size based on ``configMINIMAL_STACK_SIZE``. |
| 97 | |
| 98 | .. c:macro:: PW_THREAD_FREERTOS_CONFIG_DEFAULT_PRIORITY |
| 99 | |
| 100 | The default stack size in words. By default this uses the minimal FreeRTOS |
| 101 | priority level above the idle priority (``tskIDLE_PRIORITY + 1``). |
| 102 | |
| 103 | FreeRTOS Thread Options |
| 104 | ======================= |
| 105 | .. cpp:class:: pw::thread::freertos::Options |
| 106 | |
| 107 | .. cpp:function:: set_name(const char* name) |
| 108 | |
| 109 | Sets the name for the FreeRTOS task, note that this will be truncated |
| 110 | based on ``configMAX_TASK_NAME_LEN``. This is deep copied by FreeRTOS into |
| 111 | the task's task control block (TCB). |
| 112 | |
| 113 | .. cpp:function:: set_priority(UBaseType_t priority) |
| 114 | |
| 115 | Sets the priority for the FreeRTOS task. This must be a value between |
| 116 | ``tskIDLE_PRIORITY`` or ``0`` to ``configMAX_PRIORITIES - 1``. Higher |
| 117 | priority values have a higher priority. |
| 118 | |
| 119 | .. cpp:function:: set_stack_size(size_t size_words) |
| 120 | |
| 121 | Set the stack size in words for a dynamically thread. |
| 122 | |
| 123 | This is only available if |
| 124 | ``PW_THREAD_FREERTOS_CONFIG_DYNAMIC_ALLOCATION_ENABLED`` is enabled. |
| 125 | |
| 126 | Precondition: size_words must be >= ``configMINIMAL_STACK_SIZE`` |
| 127 | |
| 128 | .. cpp:function:: set_static_context(pw::thread::freertos::Context& context) |
| 129 | |
| 130 | Set the pre-allocated context (all memory needed to run a thread). The |
| 131 | ``StaticContext`` can either be constructed with an externally provided |
| 132 | ``std::span<StackType_t>`` stack or the templated form of |
| 133 | ``StaticContextWithStack<kStackSizeWords>`` can be used. |
| 134 | |
| 135 | |
| 136 | ----------------------------- |
| 137 | Thread Identification Backend |
| 138 | ----------------------------- |
| 139 | A backend for ``pw::thread::Id`` and ``pw::thread::get_id()`` is offerred using |
| 140 | ``xTaskGetCurrentTaskHandle()``. It uses ``DASSERT`` to ensure that it is not |
| 141 | invoked from interrupt context and if possible that the scheduler has started |
| 142 | via ``xTaskGetSchedulerState()``. |
| 143 | |
| 144 | -------------------- |
| 145 | Thread Sleep Backend |
| 146 | -------------------- |
| 147 | A backend for ``pw::thread::sleep_for()`` and ``pw::thread::sleep_until()`` is |
| 148 | offerred using ``vTaskDelay()`` if the duration is at least one tick, else |
| 149 | ``taskYIELD()`` is used. It uses ``pw::this_thread::get_id() != thread::Id()`` |
| 150 | to ensure it invoked only from a thread. |
| 151 | |
| 152 | -------------------- |
| 153 | Thread Yield Backend |
| 154 | -------------------- |
| 155 | A backend for ``pw::thread::yield()`` is offered using via ``taskYIELD()``. |
| 156 | It uses ``pw::this_thread::get_id() != thread::Id()`` to ensure it invoked only |
| 157 | from a thread. |