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commit 8c4553693bb481ce8e8c8d49157e845b51094cf9 Author: saramonteiro <[email protected]> AuthorDate: Thu Oct 8 12:36:47 2020 -0300 Documentation for the Timer Driver --- .../components/drivers/character/timer.rst | 271 +++++++++++++++++++++ 1 file changed, 271 insertions(+) diff --git a/Documentation/components/drivers/character/timer.rst b/Documentation/components/drivers/character/timer.rst index 6f2a90e..5430d62 100644 --- a/Documentation/components/drivers/character/timer.rst +++ b/Documentation/components/drivers/character/timer.rst @@ -16,3 +16,274 @@ locations: reside in ``arch/``\ *<architecture>*\ ``/src/``\ *<hardware>* directory for the specific processor *<architecture>* and for the specific *<chip>* timer peripheral devices. + +There are two ways to enable Timer Support along with the Timer Example. The first is faster and simpler. Just run the following command to use a ready config file with timer support and example included. You need to check if there's a timer config file for your specific chip. You may check it at the specific board's path: ``/boards/<arch>/<chip>/<variant>/config``. + +.. code-block:: console + + $ ./tools/configure.sh <variant>:timer + +And the second way is creating your own config file. To do so, follow the next instructions. + +Enabling the Timer Support and Example in ``menuconfing`` +--------------------------------------------------------- + + 1. Select Timer Instances + + To select these timers browse in the ``menuconfig`` using the following path: + + Go into menu :menuselection:`System Type --> <Chip> Peripheral Selection` and press :kbd:`Enter`. + + Then select one or more timers according to availability. + + 2. Enable the Timer Support + + Go into menu :menuselection:`Device Drivers --> Timer Driver Support` and press :kbd:`Enter`. Then enable: + + - [x] Timer Support + - [x] Timer Arch Implementation + + 3. Include the Timer Example + + Go into menu :menuselection:`Application Configuration --> Examples` and press :kbd:`Enter`. Then select the Timer Example. + + - [x] Timer example + + Below the option, it is possible to manually configure some parameters as the standard timer device path, the timeout, the sample rate in which the counter will be read, the number of samples to be executed, and other parameters. + +Timer Example +-------------- + +The previously selected example will basically consult the timer status, set a timer alarm interval, set a timer signal handler function to be notified at the alarm, which only increments a variable, and then it will start the timer. The application will periodically consult the timer status at the sample rate previously configured through the ``menuconfig`` to follow the time left until the timer expires. After the samples have been read, the application stops de timer. + +The `example code <https://github.com/apache/incubator-nuttx-apps/blob/master/examples/timer/timer_main.c#ref-example>`_ may be explored, its path is at ``/examples/timer/timer_main.c`` in the apps' repository. + +In NuttX, the timer driver is a character driver and when a chip supports multiple timers, each one is accessible through its respective file in ``/dev`` directory. Each timer is registered using a unique numeric identifier (i.e. ``/dev/timer0``, ``/dev/timer1``, ...). + +Use the following command to run the example: + +.. code-block:: console + + `nsh> timer` + +This command will use the timer 0. To use the others, specify it through a parameter (where x is the timer number): + +.. code-block:: console + + `nsh> timer -d /dev/timerx` + +Application Level Interface +---------------------------- + +The first necessary thing to be done in order to use the timer driver in an application is to include the header file for the NuttX timer driver. It contains the Application Level Interface to the timer driver. To do so, include: + +.. code-block:: c + + #include <nuttx/timers/timer.h> + + +At an application level, the timer functionalities may be accessed through ``ioctl`` systems calls. The available ``ioctl`` commands are: + +* TCIOC_START +* TCIOC_STOP +* TCIOC_GETSTATUS +* TCIOC_SETTIMEOUT +* TCIOC_NOTIFICATION +* TCIOC_MAXTIMEOUT + +These ``ioctl`` commands internally call lower-half layer functions and the parameters are forwarded to these functions through the ``ioctl`` system call. The return of a system call is the return of a function. +Since ``ioctl`` system calls expect a file descriptor, before using these commands, it's necessary to open the timer device special file in order to get a file descriptor. The following snippet demonstrates how to do so: + +.. code-block:: c + + /* Open the timer device */ + + printf("Open %s\n", devname); + + fd = open(devname, O_RDONLY); + if (fd < 0) + { + fprintf(stderr, "ERROR: Failed to open %s: %d\n", + devname, errno); + return EXIT_FAILURE; + } + +TCIOC_START +----------- + +The ``TCIOC_START`` command calls the ``start`` function, which is described below. + +.. c:function:: int start(void) + + The start function configures the timer, enables the interrupt if ``TCIOC_NOTIFICATION`` has already been called and finally starts the timer. + + :return: A Linux System Error Code for failing or 0 for success. + +This command may be used like so: + +.. code-block:: c + + /* Start the timer */ + + printf("Start the timer\n"); + + ret = ioctl(fd, TCIOC_START, 0); + if (ret < 0) + { + fprintf(stderr, "ERROR: Failed to start the timer: %d\n", errno); + close(fd); + return EXIT_FAILURE; + } + +TCIOC_STOP +---------- + +The ``TCIOC_STOP`` command calls the ``stop`` function, which is described below. + +.. c:function:: int stop(void) + + The stop function stops the timer and disables the interrupt. + + :return: A Linux System Error Code for failing or 0 for success. + +This command may be used like so: + +.. code-block:: c + + /* Stop the timer */ + + printf("\nStop the timer\n"); + + ret = ioctl(fd, TCIOC_STOP, 0); + if (ret < 0) + { + fprintf(stderr, "ERROR: Failed to stop the timer: %d\n", errno); + close(fd); + return EXIT_FAILURE; + } + +TCIOC_GETSTATUS +--------------- + +The ``TCIOC_GETSTATUS`` command calls the ``getstatus`` function, which is described below. + +.. c:function:: int getstatus(FAR struct timer_status_s *status) + + The getstatus function gathers the timer's current information. + + :param status: A writable pointer to a struct ``timer_status_s``. This struct contains 3 fields: ``flags`` (``uint32_t``), ``timeout`` (``uint32_t``) and ``timeleft`` (``uint32_t``). Bit 0 from `flags` indicates the timer's status, 1 indicates that the timer is running, zero it is stopped. Bit 1 from `flags` indicates if there's a callback registered. The `timeout` indicates the time interval that was configured to trigger an alarm, it is in microseconds. The `timeleft` interval indica [...] + + :return: A Linux System Error Code for failing or 0 for success. + +This command may be used like so: + +.. code-block:: c + + /* Get timer status */ + + ret = ioctl(fd, TCIOC_GETSTATUS, (unsigned long)((uintptr_t)&status)); + if (ret < 0) + { + fprintf(stderr, "ERROR: Failed to get timer status: %d\n", errno); + close(fd); + exit(EXIT_FAILURE); + } + + /* Print the timer status */ + + printf(" flags: %08lx timeout: %lu timeleft: %lu\n", + (unsigned long)status.flags, (unsigned long)status.timeout, + (unsigned long)status.timeleft); + +TCIOC_SETTIMEOUT +--------------- + +The ``TCIOC_SETTIMEOUT`` command calls the ``settimeout`` function, which is described below. + +.. c:function:: int settimeout(uint32_t timeout) + + The getstatus function sets a timeout interval to trigger the alarm and then trigger an interrupt. It defines the timer interval in which the handler will be called. + + :param timeout: An argument of type ``uint32_t`` with the timeout value in microseconds. + + :return: A Linux System Error Code for failing or 0 for success. + +This command may be used like so: + +.. code-block:: c + + /* Set the timer interval */ + + printf("Set timer interval to %lu\n", + (unsigned long)CONFIG_EXAMPLES_TIMER_INTERVAL); + + ret = ioctl(fd, TCIOC_SETTIMEOUT, CONFIG_EXAMPLES_TIMER_INTERVAL); + if (ret < 0) + { + fprintf(stderr, "ERROR: Failed to set the timer interval: %d\n", errno); + close(fd); + return EXIT_FAILURE; + } + +TCIOC_NOTIFICATION +------------------- + +The ``TCIOC_NOTIFICATION`` is used to configure the timer callback to notify the application via a signal when the timer expires. This command calls the ``setcallback`` function. Which will not be described here, since the application does not set a callback directly. Instead, the user should configure a signal handler to catch notifications, and then, configure a timer notifier to notify and to signal the previously configured signal handler. For a better performance, a separate pthread [...] + +In any case, this command expects a read-only pointer to a struct `timer_notify_s`. This struct contains 2 fields: ``pid`` (``pid_t``), that indicates the ID of the task/thread to receive the signal and ``event`` (``struct sigevent``), which describes the way a task will be notified. + +This command may be used like so: + +.. code-block:: c + + printf("Configure the notification\n"); + + notify.pid = getpid(); + notify.event.sigev_notify = SIGEV_SIGNAL; + notify.event.sigev_signo = CONFIG_EXAMPLES_TIMER_SIGNO; + notify.event.sigev_value.sival_ptr = NULL; + + ret = ioctl(fd, TCIOC_NOTIFICATION, (unsigned long)((uintptr_t)¬ify)); + if (ret < 0) + { + fprintf(stderr, "ERROR: Failed to set the timer handler: %d\n", errno); + close(fd); + return EXIT_FAILURE; + } + + +TCIOC_MAXTIMEOUT +------------------ + +The ``TCIOC_MAXTIMEOUT`` command calls the ``maxtimeout`` function, which is described below. + +.. c:function:: int maxtimeout(uint32_t *status) + + The maxtimeout function gets the maximum timeout value that can be configured. + + :param maxtimeout: A writable pointer to a variable of ``uint32_t`` type in which the value will be stored. + :return: A Linux System Error Code for failing or 0 for success. + +This command may be used like so: + +.. code-block:: c + + /* Get the maximum timer timeout */ + + printf("Get the maximum timer timeout\n"); + + ret = ioctl(fd, TCIOC_MAXTIMEOUT, (uint32_t*)(&max_timeout)); + if (ret < 0) + { + fprintf(stderr, "ERROR: Failed to reat the timer's maximum timeout: %d\n", errno); + close(fd); + return EXIT_FAILURE; + } + + /* Print the maximum supported timeout */ + + printf("Maximum supported timeout: %" PRIu32 "\n", max_timeout); + + +Those snippets were taken from the Example which provides a great resource to demonstrate how to use those ``ioctl`` commands. +
