uC-OS-III Features os_cfg.h

Compile-time configuration allows users to determine which features to enable and those features that are not needed. With compile-time configuration, the code and data sizes of µC/OS-III (i.e., its footprint) can be reduced by enabling only the desired functionality.

Compile-time configuration is accomplished by setting a number of #define constants in a file called os_cfg.h that the application is expected to provide. You simply copy os_cfg.h into the application directory and change the copied file to satisfy the application’s requirements. This way, os_cfg.h is not recreated from scratch.

The compile-time configuration #defines are listed below as per the sections and order found in os_cfg.h.

Miscellaneous Options

OS_CFG_APP_HOOKS_EN

When set to DEF_ENABLED, this option specifies that application-defined hooks can be called from µC/OS-III’s hooks. This allows the application code to extend the functionality of µC/OS-III. Specifically:

Application hook functions could be declared as shown in the code below.

It’s also up to a user to set the value of the pointers so that they point to the appropriate functions as shown below. The pointers do not have to be set in main() but, you can set them after calling OSInit().

Note that not every hook function need to be defined, only the ones the user wants to place in the application code.

Also, if you don't intend to extend µC/OS-III’s hook through these application hooks, you can set OS_CFG_APP_HOOKS_EN to DEF_DISABLED  to save RAM (i.e., the pointers).

OS_CFG_ARG_CHK_EN

OS_CFG_ARG_CHK_EN determines whether the user wants most of µC/OS-III functions to perform argument checking. When set to DEF_ENABLED, µC/OS-III ensures that pointers passed to functions are non-NULL, that arguments passed are within allowable range, that options are valid, and more. When set to DEF_DISABLED, those arguments are not checked and the amount of code space and processing time required by µC/OS-III is reduced. You would set OS_CFG_ARG_CHK_EN to DEF_DISABLED if you are certain that the arguments will always be correct.

µC/OS-III performs argument checking in close to 50 functions. Therefore, you can save a few hundred bytes of code space by disabling this check. However, you should always enable argument checking until you are certain the code can be trusted.

OS_CFG_CALLED_FROM_ISR_CHK_EN

OS_CFG_CALLED_FROM_ISR_CHK_EN determines whether most of µC/OS-III functions are to confirm that the function is not called from an ISR. In other words, most of the functions from µC/OS-III should be called by task-level code except “post” type functions (which can also be called from ISRs). By setting this DEF_ENABLED, µC/OS-III is told to make sure that functions that are only supposed to be called by tasks are not called by ISRs. It’s highly recommended to set this to  DEF_ENABLED  until you are absolutely sure that the code is behaving correctly and that task-level functions are always called from tasks. You can set this to  DEF_DISABLED  to save code space and, of course, processing time.

µC/OS-III performs this check in approximately 50 functions. Therefore, you can save a few hundred bytes of code space by disabling this check.

OS_CFG_DBG_EN

When set to DEF_ENABLED, this configuration adds ROM constants located in os_dbg.c to help support kernel aware debuggers. Specifically, a number of named ROM variables can be queried by a debugger to find out about compiled-in options. For example, a debugger can find out the size of a OS_TCB, µC/OS-III’s version number, the size of an event flag group (OS_FLAG_GRP), and much more.

OS_CFG_DYN_TICK_EN

When set to DEF_ENABLED, µC/OS-III will use a dynamic ticking mechanism instead of the traditional continuous tick. This allows µC/OS-III to sleep until a task needs to be awakened, instead of waking up every 1/OS_CFG_TICK_RATE_HZ seconds to find no that no tasks need to be awakened. This can be used to save power since the scheduler is run only when strictly necessary.

Note that the use of this feature requires a proper Board Support Package (BSP) that implements the API described in Board Support Package.

OS_CFG_INVALID_OS_CALLS_CHK_EN

When set to DEF_ENABLED, µC/OS-III will validate the call and check that the kernel is indeed running before performing the function. You would set OS_CFG_INVALID_OS_CALLS_CHK_EN to DEF_DISABLED if you are sure that the OS functions will be called only once OSStart() has been called. 

µC/OS-III performs this check in more than 40 functions. Therefore, you can save a few hundred bytes of code space by disabling this check.

OS_CFG_ISR_POST_DEFERRED_EN

Warning, this feature is DEPRECATED and will be removed in a future release of µC/OS-III.

When set to  DEF_ENABLED , OS_CFG_ISR_POST_DEFERRED_EN reduces interrupt latency since interrupts are not disabled during most critical sections of code within µC/OS-III. Instead, the scheduler is locked during the processing of these critical sections. The advantage of setting this to DEF_ENABLED is that interrupt latency is lower, however, ISR to task response is slightly higher. It is recommended to set OS_CFG_ISR_POST_DEFERRED_EN to DEF_ENABLED  when enabling the following services, since setting this to  DEF_DISABLED  would potentially make interrupt latency unacceptably high:

The compromise to make is:

OS_CFG_ISR_POST_DEFERRED_EN set to  DEF_ENABLED

Short interrupt latency, longer ISR-to-task response.

OS_CFG_ISR_POST_DEFERRED_EN set to  DEF_DISABLED

Long interrupt latency (see table above), shorter ISR-to-task response.

OS_CFG_OBJ_TYPE_CHK_EN

OS_CFG_OBJ_TYPE_CHK_EN determines whether most of µC/OS-III functions should check to see if the function is manipulating the proper object. In other words, if attempting to post to a semaphore, is the user in fact passing a semaphore object or another object by mistake? It is recommended to set  OS_CFG_OBJ_TYPE_CHK_EN to DEF_ENABLED until absolutely certain that the code is behaving correctly and the user code is always pointing to the proper objects. You would set this to DEF_DISABLED  to save code space as well as data space.

µC/OS-III object type checking is done nearly 40 times, and it is possible to save a few hundred bytes of code space and processing time by disabling this check.

OS_CFG_TS_EN

When OS_CFG_TS_EN is set to DEF_ENABLED, it enables the timestamp facilities provided by µC/CPU. This allows the user and the kernel to measure the time between various events. For example, the time spent by a task pending on an object, the maximum interrupt disable time (if CPU_CFG_INT_DIS_MEAS_EN is set to  DEF_ENABLED), the time the scheduler is locked, etc. This option is mostly useful in profiling and performance measurement contexts. To save space and processing time, set this option to  DEF_DISABLED .

Note that to use the timestamp facilities the µC/CPU Board Support Package should implement the functions described in cpu_bsp.c and cpu_bsp.h.

OS_CFG_PEND_MULTI_EN

Warning, this feature is DEPRECATED and will be removed in a future release of µC/OS-III.

When this option is set to DEF_ENABLED, it allows the user to pend on multiple objects (message queues and semaphores only) at once.

OS_CFG_PRIO_MAX

OS_CFG_PRIO_MAX specifies the maximum number of priorities available in the application. Specifying OS_CFG_PRIO_MAX to just the number of priorities the user intends to use, reduces the amount of RAM needed by µC/OS-III.

In µC/OS-III, task priorities can range from 0 (highest priority) to a maximum of 255 (lowest possible priority) when the data type OS_PRIO is defined as a CPU_INT08U. However, in µC/OS-III, there is no practical limit to the number of available priorities. Specifically, if defining OS_PRIO as a CPU_INT16U, there can be up to 65536 priority levels. It is recommended to leave OS_PRIO defined as a CPU_INT08U and use only 256 different priority levels (i.e., 0..255), which is generally sufficient for every application. You should always set the value of OS_CFG_PRIO_MAX to even multiples of 8 (8, 16, 32, 64, 128, 256, etc.). The higher the number of different priorities, the more RAM µC/OS-III will consume.

An application cannot create tasks with a priority number higher than or equal to OS_CFG_PRIO_MAX. In fact, µC/OS-III reserves priority OS_CFG_PRIO_MAX-2 and OS_CFG_PRIO_MAX-1 for itself; OS_CFG_PRIO_MAX-1 is reserved for the Idle Task OS_IdleTask(), if used. Additionally, do not use priority 0 for an application since it is reserved by µC/OS-III’s ISR handler task. The priorities of the application tasks can therefore take a value between 2 and OS_CFG_PRIO_MAX–3 (inclusive).

To ensure proper operation of µC/OS-III and it's services, care should be taken when setting the priorities of other system task such as the Tick Task, the Statistics Task and the Timer Task in os_cfg_app.h.

To summarize, there are two priority levels to avoid in an application:

OS_CFG_SCHED_LOCK_TIME_MEAS_EN

When set to DEF_ENABLED ,  OS_CFG_SCHED_LOCK_TIME_MEAS_EN allows µC/OS-III to use the timestamp facilities (provided  OS_CFG_TS_EN is also set to  DEF_ENABLED) to measure the peak amount of time that the scheduler is locked. Use this feature to profile the application, the deployed application should set this to  DEF_DISABLED .

OS_CFG_SCHED_ROUND_ROBIN_EN

Set OS_CFG_SCHED_ROUND_ROBIN_EN to DEF_ENABLED  to use the Round Robin Scheduler. This is only useful when there is multiple tasks sharing the same priority, if this is not your case, set this option to DEF_DISABLED . See Round-Robin Scheduling for more information.

OS_CFG_STK_SIZE_MIN

OS_CFG_STK_SIZE_MIN specifies the minimum stack size (in CPU_STK elements) for each task. This is used by µC/OS-III to verify that sufficient stack space is provided for each task when the task is created. Suppose the full context of a processor consists of 16 registers of 32 bits. Also, suppose CPU_STK is declared as being of type CPU_INT32U, at a bare minimum, OS_CFG_STK_SIZE_MIN should be set to 16. However, it would be quite unwise to not accommodate for storage of local variables, function call returns, and possibly nested ISRs. Refer to the “port” of the processor used to see how to set this minimum. Again, this is a safeguard to make sure task stacks have sufficient space.

Event Flag Configuration

OS_CFG_FLAG_EN

When OS_CFG_FLAG_EN is set to DEF_ENABLED, it enables the event flag services and data structures. If event flags are not needed, set this to DEF_DISABLED. It reduces the amount of code and data space needed by µC/OS-III. Note than when OS_CFG_FLAG_EN is set to DEF_DISABLED , it is not necessary to enable or disable any of the other OS_CFG_FLAG_xxx options in this section.

OS_CFG_FLAG_DEL_EN

If your application needs to delete event flags with  OSFlagDel()  once they're created, set OS_CFG_FLAG_DEL_EN to DEF_ENABLED, if not, set this option to DEF_DISABLED. Critical applications should not delete kernel objects once the kernel is started.

OS_CFG_FLAG_MODE_CLR_EN

If your application requires to wait until a event is cleared, set OS_CFG_FLAG_MODE_CLR_EN to DEF_ENABLED, if not set this to DEF_DISABLED. Generally, you would wait for event flags to be set. However, the user may also want to wait for event flags to be clear and in this case, enable this option.

OS_CFG_FLAG_PEND_ABORT_EN

When OS_CFG_FLAG_PEND_ABORT_EN is set to DEF_ENABLED, it enables the generation of the function OSFlagPendAbort(). If your application does not require fault-aborts on event flags, set this option to DEF_DISABLED.

Memory Management Configuration

OS_CFG_MEM_EN

When OS_CFG_MEM_EN is set to DEF_ENABLED, it enables the µC/OS-III partition memory manager. If your application does not require the partitionned memory manager, set this to DEF_DISABLE to reduce µC/OS-III's code and data space usage.

Mutal Exclusion Semaphore Configuration

OS_CFG_MUTEX_EN

When OS_CFG_MUTEX_EN is set to DEF_ENABLED, it enables the mutual exclusion semaphore services and data structures. If your application does not require mutexes, set this option to DEF_DISABLED to reduce the amount of code and data space needed by µC/OS-III. When OS_CFG_MUTEX_EN is set to DEF_DISABLED, there is no need to enable or disable any of the other OS_CFG_MUTEX_XXX options in this section.

OS_CFG_MUTEX_DEL_EN

If your application needs to delete mutexes with  OSMutexDel ()  once they're created, set  OS_CFG_MUTEX_DEL_EN  to DEF_ENABLED, if not, set this option to DEF_DISABLED. Critical applications should not delete kernel objects once the kernel is started.

OS_CFG_MUTEX_PEND_ABORT_EN

When OS_CFG_MUTEX_PEND_ABORT_EN is set to DEF_ENABLED, it enables the generation of the function  OSMutexPendAbort(). If your application does not require fault-aborts on mutexes, set this option to DEF_DISABLED.

Message Queue Configuration

OS_CFG_Q_EN

When OS_CFG_Q_EN is set to  DEF_ENABLED , it enables the message queue services and data structures. If your application does not require mutexes, set this option to DEF_DISABLED to reduce the amount of code and data space needed by µC/OS-III. When OS_CFG_Q_EN is set to DEF_DISABLED, there is no need to enable or disable any of the other OS_CFG_Q_XXX options in this section.

OS_CFG_Q_DEL_EN

If your application needs to delete message queues with OSQDel() once they're created, set OS_CFG_Q_DEL_EN to DEF_ENABLED, if not, set this option to DEF_DISABLED. Critical applications should not delete kernel objects once the kernel is started.

OS_CFG_Q_FLUSH_EN

When OS_CFG_Q_FLUSH_EN is set to DEF_ENABLED, it allows your application to flush, or clear, a message queue with OSQFlush(). If this feature is not needed, set this option to  DEF_DISABLED .

OS_CFG_Q_PEND_ABORT_EN

When OS_CFG_Q_PEND_ABORT_EN is set to DEF_ENABLED, it enables the generation of the function OSQPendAbort(). If your application does not require fault-aborts on message queues, set this option to DEF_DISABLED.

Semaphore Configuration

OS_CFG_SEM_EN

When OS_CFG_SEM_EN is set to  DEF_ENABLED , it enables the semaphore services and data structures. If your application does not require semaphores, set this option to DEF_DISABLED to reduce the amount of code and data space needed by µC/OS-III. When OS_CFG_SEM_EN is set to DEF_DISABLED, there is no need to enable or disable any of the other OS_CFG_SEM_XXX options in this section.

OS_CFG_SEM_DEL_EN

If your application needs to delete semaphores with  OSSemDel ()  once they're created, set OS_CFG_SEM_DEL_EN to DEF_ENABLED, if not, set this option to DEF_DISABLED. Critical applications should not delete kernel objects once the kernel is started.

OS_CFG_SEM_PEND_ABORT_EN

When OS_CFG_SEM_PEND_ABORT_EN is set to DEF_ENABLED, it enables the generation of the function  OSSemPendAbort(). If your application does not require fault-aborts on semaphores queues, set this option to DEF_DISABLED.

OS_CFG_SEM_SET_EN

If your application needs to explicitly set the value of a semaphore with  OSSemSet()  at another time than it's creation, set OS_CFG_SEM_SET_EN to DEF_ENABLE, if not, set this option to DEF_DISABLED.

Monitor Configuration

OS_CFG_MON_EN

When OS_CFG_MON_EN is set to  DEF_ENABLED , it enables the monitor services and data structures. If your application does not require monitors, set this option to DEF_DISABLED to reduce the amount of code and data space needed by µC/OS-III.

OS_CFG_MON_DEL_EN

If your application needs to delete a monitor with OSMonDel()  once they're created, set OS_CFG_MON_DEL_EN to DEF_ENABLED, if not, set this option to DEF_DISABLED. Critical applications should not delete kernel objects once the kernel is started.

Task Management Options

OS_CFG_STAT_TASK_EN

OS_CFG_STAT_TASK_EN specifies whether or not to enable µC/OS-III’s statistic task, as well as its initialization function. When set to  DEF_ENABLED , the statistic task OS_StatTask() and the statistic task initialization function are enabled. OS_StatTask() computes the CPU usage of an application, the stack usage of each task, the CPU usage of each task at run time and more.

When enabled, OS_StatTask() executes at a rate of OS_CFG_STAT_TASK_RATE_HZ (see os_cfg_app.h), and computes the value of OSStatTaskCPUUsage, which is a variable that contains the percentage of CPU used by the application. OS_StatTask() calls OSStatTaskHook() every time it executes so that the user can add his own statistics as needed. See os_stat.c for details on the statistic task. The priority of OS_StatTask() is configurable by the application code (see os_cfg_app.h).

OS_StatTask() computes stack usage of each task created when the option OS_CFG_STAT_TASK_STK_CHK_EN is set to  DEF_ENABLED . In this case, OS_StatTask() calls OSTaskStkChk() for each task and the result is placed in the task’s TCB. The .StkFree and .StkUsed fields of the task’s TCB represent the amount of free space (in CPU_STK elements) and amount of used space (in CPU_STK elements), respectively.

When OS_CFG_STAT_TASK_EN is set to DEF_DISABLED, all variables used by the statistic task are not declared (see os.h). This, of course, reduces the amount of RAM needed by µC/OS-III when not enabling the statistic task.

OS_CFG_STAT_TASK_STK_CHK_EN

When set to DEF_ENABLED, this option allows the statistic task to call OSTaskStkChk() for each task created. Note that for this to happen, OS_CFG_STAT_TASK_EN must also be set to  DEF_ENABLED . However, you can call OSStatStkChk() from one of the tasks to obtain this information about the tasks.

OS_CFG_TASK_CHANGE_PRIO_EN

If your application needs to dynamically change a task's priority using OSTaskChangePrio()  , set OS_CFG_TASK_CHANGE_PRIO_EN to DEF_ENABLED. If not, set this option to DEF_DISABLED. Note that the new priority has to be available and not currently in-use by a kernel task.

OS_CFG_TASK_DEL_EN

If your application needs to delete tasks using OSTaskDel(), set OS_CFG_TASK_DEL_EN to DEF_ENABLED. If not, set this option to DEF_DISABLED. Note that critical applications should not delete tasks once the kernel is started.

OS_CFG_TASK_IDLE_EN

Setting OS_CFG_TASK_IDLE_EN to DEF_ENABLED allows µC/OS-III to create it's Idle Task at priority OS_CFG_PRIO_MAX-1. However, to save data space, it is possible to remove the Idle Task. To do so, set this option to  DEF_DISABLED. Doing so will move the functionality of the Idle Task within the OSSched() function. The same counters will be incremented and the same hooks will be called under the same circumstances.

OS_CFG_TASK_PROFILE_EN

To enable the performance profiling tools within µC/OS-III, set OS_CFG_TASK_PROFILE_EN to DEF_ENABLED. Doing so allows variables to be allocated in each task’s OS_TCB to hold performance data about each task. When enabled, each task will have variables to keep track of the number of times a task is switched in, the task execution time, the CPU usage percentage of the task relative to the other tasks and more. The information made available with this feature is highly useful when debugging, but requires extra RAM. To save data and code space, set this option to  DEF_DISABLED after your are certain that you application is profiled and works correctly.

OS_CFG_TASK_Q_EN

When OS_CFG_TASK_Q_EN is set to DEF_ENABLED, it  allows the generation of the OSTaskQ???() functions used to send and receive messages directly to and from tasks and ISRs. Sending messages directly to a task is more efficient than sending messages using a traditional message queue because there is no pend list associated with messages sent to a task. If your application does not require task-level message queues, set this option to DEF_DISABLED. Note that if this option is set to DEF_DISABLED , the  OS_CFG_TASK_Q_PEND_ABORT_EN configuration option is ignored.

OS_CFG_TASK_Q_PEND_ABORT_EN

When OS_CFG_TASK_Q_PEND_ABORT_EN is set to DEF_ENABLED, it enables the generation of the function OSTaskQPendAbort(). If your application does not require fault-aborts on task-level message queues, set this option to DEF_DISABLED.

OS_CFG_TASK_REG_TBL_SIZE

This constant allows each task to have task context variables. Use task variables to store such elements as “errno”, task identifiers and other task-specific values. The number of variables that a task contains is set by OS_CFG_TASK_REG_TBL_SIZE. Each variable is identified by a unique identifier from 0 to OS_CFG_TASK_REG_TBL_SIZE-1. Also, each variable is declared as having an OS_REG data type (see os_type.h). If OS_REG is a CPU_INT32U, all variables in this table are of this type. To disable the usage of task context variables, set this option to 0u.

OS_CFG_TASK_STK_REDZONE_EN

While debugging, it is useful to determine if a task overflowed it's stack space. To do so, set OS_CFG_TASK_STK_REDZONE_EN to DEF_ENABLED. Then, every time a task is switched in after an interrupt, it's stack is checked. If the monitored zone located at the end of a task's stack is corrupted, a software exception is thrown. To disable this feature, set this option to DEF_DISABLED. Note that the effectively usable stack space is the task stack size minus OS_CFG_TASK_STK_REDZONE_DEPTH.

OS_CFG_TASK_STK_REDZONE_DEPTH

The default monitored zone, located at the end of a task's stack, is 8 CPU_STK elements long. To change the size of the monitored zone, change this option accordingly. If OS_CFG_TASK_STK_REDZONE_EN is set to DEF_DISABLED, this value is ignored.

OS_CFG_TASK_SEM_PEND_ABORT_EN

When OS_CFG_TASK_SEM_PEND_ABORT_EN is set to DEF_ENABLED, it enables the generation of the function OSTaskSemPendAbort(). If your application does not require fault-aborts on task-level semaphores, set this option to DEF_DISABLED.

OS_CFG_TASK_SUSPEND_EN

If your application requires the ability to explicitly suspend and resume the execution of tasks, set OS_CFG_TASK_SUSPEND_EN to DEF_ENABLED. Doing so, allows the generation of the OSTaskSuspend() and OSTaskResume() functions used to suspend and resume tasks, respectively. Note that other effects are additive with the suspension. For example, if a suspended task is pending on a semaphore that becomes available, the task will not run until it's explicitly resumed with OSTaskResume(). Also, the suspension of a task can be nested. To resume a task, you must call OSTaskResume() the same number of times  OSTaskSuspend() was called. If your application does not require this feature, set this option to DEF_DISABLED.

OS_CFG_TASK_TICK_EN

To keep the traditional behavior, set OS_CFG_TASK_TICK_EN to DEF_ENABLED. If your application does not require any form of timeouts or time keeping, either with timeouts on kernel objects or delayed execution times, you may set OS_CFG_TASK_TICK_EN to DEF_DISABLED. Doing so, removes all time keeping facilities from µC/OS-III. Removing the Tisk Task from µC/OS-III allows the user to save code and data space. However, the users looses the ability to use timeouts and delays.

Task Local Storage Configuration

OS_CFG_TLS_TBL_SIZE

If your application requires task local storage, set OS_CFG_TLS_TBL_SIZE to a non-null value. This value will determine the size of the Task Local Storage Table (TLS_Tbl, member of OS_TCB) present in each task. To disable TLS, set this option to 0u.

Time Management Options

OS_CFG_TIME_DLY_HMSM_EN

If your application requires the ability to delay a task for a specified number of hours, minutes, seconds and milliseconds, set OS_CFG_TIME_DLY_HMSM_EN to DEF_ENABLED. This will allow the generation of the OSTimeDlyHMSM() function. Otherwise, set this option to DEF_DISABLED.

OS_CFG_TIME_DLY_RESUME_EN

When OS_CFG_TIME_DLY_RESUME_EN is set to DEF_ENABLED, it allows applications to resume a previously delayed task, using the function OSTimeDlyResume(), without waiting for the entire delay. If you do not require this feature, set this option to DEF_DISABLED.

Timer Management Options

OS_CFG_TMR_EN

When OS_CFG_TMR_EN is set to DEF_ENABLED, it enables the timer management services. If your application does no require programmable timers, set this option to DEF_DISABLED to reduce µC/OS-III's required code and data space.

OS_CFG_TMR_DEL_EN

If your application needs to delete timers with OSTmrDel()  once they're created, set OS_CFG_TMR_DEL_EN to DEF_ENABLED, if not, set this option to DEF_DISABLED. Critical applications should not delete kernel objects once the kernel is started.

µC/Trace Configuration

TRACE_CFG_EN

Although not specifically part of µC/OS-III, µC/Trace, a Windows-based RTOS Event Analyzer (i.e. tool) that is fully integrated in the latest version of µC/OS-III. µC/Trace functionality is enabled by setting TRACE_CFG_EN to DEF_ENABLED . You will need to have purchased the µC/Trace product in order to set TRACE_CFG_EN to DEF_ENABLED  or else your compiler will complain about missing macros and functions. Consult the Micrium website for details and availability of this highly useful tool.