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authorSebastian Huber <sebastian.huber@embedded-brains.de>2016-12-21 10:55:46 +0100
committerSebastian Huber <sebastian.huber@embedded-brains.de>2016-12-21 11:08:32 +0100
commite7f40f04d39d3d87d30b50a02bab90a72a9dae61 (patch)
tree1b7ef47bf387ad1ff158d827aa9746aa321c5538
parentf5170100f1a2fe449c327cb6786c4f3202cf07e8 (diff)
downloadrtems-docs-e7f40f04d39d3d87d30b50a02bab90a72a9dae61.tar.bz2
Rework Clock Driver chapter
Update #2737.
-rw-r--r--bsp-howto/clock.rst237
1 files changed, 137 insertions, 100 deletions
diff --git a/bsp-howto/clock.rst b/bsp-howto/clock.rst
index f1d4c3b..55c94ac 100644
--- a/bsp-howto/clock.rst
+++ b/bsp-howto/clock.rst
@@ -17,75 +17,126 @@ system.
clock tick work properly. See the *Clock Manager* chapter of the *RTEMS
Application C User's Guide* for more details.
-- An optional time counter to generate timestamps of the uptime and wall clock
- time.
+- An optional `timecounter <http://www.freebsd.dk/pubs/timecounter.pdf>`_ to
+ provide timestamps of the uptime and wall clock time with higher resolution
+ than the clock tick.
The clock driver is usually located in the :file:`clock` directory of the BSP.
-Clock drivers should use the :dfn:`Clock Driver Shell` available via the
-:file:`clockdrv_shell.h` include file.
-
-Clock Driver Shell
-==================
-
-The :dfn:`Clock Driver Shell` include file defines the clock driver functions
-declared in ``#include <rtems/clockdrv.h>`` which are used by RTEMS
-configuration file ``#include <rtems/confdefs.h>``. In case the application
-configuration defines ``#define CONFIGURE_APPLICATION_NEEDS_CLOCK_DRIVER``,
-then the clock driver is registered and should provide its services to the
-operating system. A hardware specific clock driver must provide some
-functions, defines and macros for the :dfn:`Clock Driver Shell` which are
-explained here step by step. A clock driver file looks in general like this.
+Clock drivers must use the :dfn:`Clock Driver Shell` available via the
+`clockdrv_shell.h <https://git.rtems.org/rtems/tree/c/src/lib/libbsp/shared/clockdrv_shell.h>`_
+include file. This include file is not a normal header file and instead
+defines the clock driver functions declared in ``#include <rtems/clockdrv.h>``
+which are used by RTEMS configuration file ``#include <rtems/confdefs.h>``. In
+case the application configuration defines
+``#define CONFIGURE_APPLICATION_NEEDS_CLOCK_DRIVER``, then the clock driver is
+registered and should provide its services to the operating system. The clock
+tick interval is determined by the application configuration via
+``#define CONFIGURE_MICROSECONDS_PER_TICK`` and can be obtained via
+``rtems_configuration_get_microseconds_per_tick()``.
+
+A hardware-specific clock driver must provide some functions, defines and
+macros for the :dfn:`Clock Driver Shell` which are explained here step by step.
+A clock driver file looks in general like this.
.. code-block:: c
/*
- * A section with functions, defines and macros to provide hardware specific
+ * A section with functions, defines and macros to provide hardware-specific
* functions for the Clock Driver Shell.
*/
- #include "../../../shared/clockdrv_shell.h"
-Initialization
---------------
+ #include "../../../shared/clockdrv_shell.h"
Depending on the hardware capabilities one out of three clock driver variants
must be selected.
-- The most basic clock driver provides only a periodic interrupt service
- routine which calls ``rtems_clock_tick()``. The interval is determined by
- the application configuration via ``#define CONFIGURE_MICROSECONDS_PER_TICK``
- and can be obtained via ``rtems_configuration_get_microseconds_per_tick()``.
- The timestamp resolution is limited to the clock tick interval.
+Timecounter
+ The variant which provides all features needs a free running hardware
+ counter and a periodic clock tick interrupt. This variant is mandatory in
+ SMP configurations.
-- In case the hardware lacks support for a free running counter, then the
- module used for the clock tick may provide support for timestamps with a
- resolution below the clock tick interval. For this so called simple
- timecounters can be used.
+Simple Timecounter
+ A simple timecounter can be used if the hardware provides no free running
+ hardware counter and only a periodic hardware counter synchronous to the
+ clock tick interrupt is available.
-- The desired variant uses a free running counter to provide accurate
- timestamps. This variant is mandatory on SMP configurations.
+Clock Tick Only
+ The most basic clock driver provides only a periodic clock tick interrupt.
+ The timestamp resolution is limited to the clock tick interval.
-Clock Tick Only Variant
-~~~~~~~~~~~~~~~~~~~~~~~
+Initialization
+==============
+
+Timecounter Variant
+~~~~~~~~~~~~~~~~~~~
+
+This variant is preferred since it is the most efficient and yields the most
+accurate timestamps. It is also mandatory in SMP configurations to obtain
+valid timestamps. The hardware must provide a periodic interrupt to service
+the clock tick and a free running counter for the timecounter. The free
+running counter must have a power of two period. The ``tc_counter_mask`` must
+be initialized to the free running counter period minus one, e.g. for a 17-bit
+counter this is ``0x0001ffff``. The ``tc_get_timecount`` function must return
+the current counter value (the counter values must increase, so if the counter
+counts down, a conversion is necessary). Use
+``RTEMS_TIMECOUNTER_QUALITY_CLOCK_DRIVER`` for the ``tc_quality``. Set
+``tc_frequency`` to the frequency of the free running counter in Hz. All other
+fields of the ``struct timecounter`` must be zero initialized. Install the
+initialized timecounter via ``rtems_timecounter_install()``.
+
+For an example see the `QorIQ clock driver
+<https://git.rtems.org/rtems/tree/c/src/lib/libbsp/powerpc/qoriq/clock/clock-config.c>`_.
.. code-block:: c
- static void some_support_initialize_hardware( void )
+ #include <rtems/timecounter.h>
+
+ static struct timecounter some_tc;
+
+ static uint32_t some_tc_get_timecount( struct timecounter *tc )
{
- /* Initialize hardware */
+ some.free_running_counter;
}
- #define Clock_driver_support_initialize_hardware() \
- some_support_initialize_hardware()
+ static void some_support_initialize_hardware( void )
+ {
+ uint64_t us_per_tick;
+ uint32_t counter_frequency_in_hz;
+ uint32_t counter_ticks_per_clock_tick;
- /* Indicate that this clock driver lacks a proper timecounter in hardware */
+ us_per_tick = rtems_configuration_get_microseconds_per_tick();
+ counter_frequency_in_hz = some_tc_get_frequency();
- #define CLOCK_DRIVER_USE_DUMMY_TIMECOUNTER
+ /*
+ * The multiplication must be done in 64-bit arithmetic to avoid an integer
+ * overflow on targets with a high enough counter frequency.
+ */
+ counter_ticks_per_clock_tick =
+ (uint32_t) ( counter_frequency_in_hz * us_per_tick ) / 1000000;
+
+ /*
+ * Initialize hardware and set up a periodic interrupt for the configuration
+ * based counter ticks per clock tick.
+ */
+
+ some_tc.tc_get_timecount = some_tc_get_timecount;
+ some_tc.tc_counter_mask = 0xffffffff;
+ some_tc.tc_frequency = frequency;
+ some_tc.tc_quality = RTEMS_TIMECOUNTER_QUALITY_CLOCK_DRIVER;
+ rtems_timecounter_install( &some_tc );
+ }
+
+ #define Clock_driver_support_initialize_hardware() \
+ some_support_initialize_hardware()
#include "../../../shared/clockdrv_shell.h"
Simple Timecounter Variant
~~~~~~~~~~~~~~~~~~~~~~~~~~
+For an example see the `ERC32 clock driver
+<https://git.rtems.org/rtems/tree/c/src/lib/libbsp/sparc/erc32/clock/ckinit.c>`_.
+
.. code-block:: c
#include <rtems/timecounter.h>
@@ -118,84 +169,56 @@ Simple Timecounter Variant
static void some_support_initialize_hardware( void )
{
- uint32_t frequency = 123456;
- uint64_t us_per_tick = rtems_configuration_get_microseconds_per_tick();
- uint32_t timecounter_ticks_per_clock_tick =
- ( frequency * us_per_tick ) / 1000000;
+ uint64_t us_per_tick;
+ uint32_t counter_frequency_in_hz;
+ uint32_t counter_ticks_per_clock_tick;
+
+ us_per_tick = rtems_configuration_get_microseconds_per_tick();
+ counter_frequency_in_hz = some_tc_get_frequency();
+ counter_ticks_per_clock_tick =
+ (uint32_t) ( counter_frequency_in_hz * us_per_tick ) / 1000000;
/* Initialize hardware */
+
rtems_timecounter_simple_install(
&some_tc,
- frequency,
- timecounter_ticks_per_clock_tick,
+ counter_frequency_in_hz,
+ counter_ticks_per_clock_tick,
some_tc_get_timecount
);
}
#define Clock_driver_support_initialize_hardware() \
- some_support_initialize_hardware()
+ some_support_initialize_hardware()
#define Clock_driver_timecounter_tick() \
- some_tc_tick()
+ some_tc_tick()
#include "../../../shared/clockdrv_shell.h"
-Timecounter Variant
-~~~~~~~~~~~~~~~~~~~
+Clock Tick Only Variant
+~~~~~~~~~~~~~~~~~~~~~~~
-This variant is preferred since it is the most efficient and yields the most
-accurate timestamps. It is also mandatory on SMP configurations to obtain
-valid timestamps. The hardware must provide a periodic interrupt to service
-the clock tick and a free running counter for the timecounter. The free
-running counter must have a power of two period. The ``tc_counter_mask`` must
-be initialized to the free running counter period minus one, e.g. for a 32-bit
-counter this is 0xffffffff. The ``tc_get_timecount`` function must return the
-current counter value (the counter values must increase, so if the counter
-counts down, a conversion is necessary). Use
-``RTEMS_TIMECOUNTER_QUALITY_CLOCK_DRIVER`` for the ``tc_quality``. Set
-``tc_frequency`` to the frequency of the free running counter in Hz. All other
-fields of the ``struct timecounter`` must be zero initialized. Install the
-initialized timecounter via ``rtems_timecounter_install()``.
+For an example see the `Motrola 68360 clock driver
+<https://git.rtems.org/rtems/tree/c/src/lib/libbsp/m68k/gen68360/clock/clock.c>`_.
.. code-block:: c
- #include <rtems/timecounter.h>
-
- static struct timecounter some_tc;
-
- static uint32_t some_tc_get_timecount( struct timecounter *tc )
- {
- some.free_running_counter;
- }
-
static void some_support_initialize_hardware( void )
{
- uint64_t us_per_tick = rtems_configuration_get_microseconds_per_tick();
- uint32_t frequency = 123456;
-
- /*
- * The multiplication must be done in 64-bit arithmetic to avoid an integer
- * overflow on targets with a high enough counter frequency.
- */
- uint32_t interval = (uint32_t) ( ( frequency * us_per_tick ) / 1000000 );
-
- /*
- * Initialize hardware and set up a periodic interrupt for the configuration
- * based interval.
- */
- some_tc.tc_get_timecount = some_tc_get_timecount;
- some_tc.tc_counter_mask = 0xffffffff;
- some_tc.tc_frequency = frequency;
- some_tc.tc_quality = RTEMS_TIMECOUNTER_QUALITY_CLOCK_DRIVER;
- rtems_timecounter_install( &some_tc );
+ /* Initialize hardware */
}
#define Clock_driver_support_initialize_hardware() \
- some_support_initialize_hardware()
+ some_support_initialize_hardware()
+
+ /* Indicate that this clock driver lacks a proper timecounter in hardware */
+
+ #define CLOCK_DRIVER_USE_DUMMY_TIMECOUNTER
#include "../../../shared/clockdrv_shell.h"
Install Clock Tick Interrupt Service Routine
---------------------------------------------
+============================================
The clock driver must provide a function to install the clock tick interrupt
service routine via ``Clock_driver_support_install_isr()``.
@@ -221,14 +244,14 @@ service routine via ``Clock_driver_support_install_isr()``.
}
#define Clock_driver_support_install_isr( isr, old ) \
- some_support_install_isr( isr )
+ some_support_install_isr( isr )
#include "../../../shared/clockdrv_shell.h"
Support At Tick
----------------
+===============
-The hardware specific support at tick is specified by
+The hardware-specific support at tick is specified by
``Clock_driver_support_at_tick()``.
.. code-block:: c
@@ -239,16 +262,16 @@ The hardware specific support at tick is specified by
}
#define Clock_driver_support_at_tick() \
- some_support_at_tick()
+ some_support_at_tick()
#include "../../../shared/clockdrv_shell.h"
System Shutdown Support
------------------------
+=======================
The :dfn:`Clock Driver Shell` provides the routine ``Clock_exit()`` that is
scheduled to be run during system shutdown via the ``atexit()`` routine. The
-hardware specific shutdown support is specified by
+hardware-specific shutdown support is specified by
``Clock_driver_support_shutdown_hardware()`` which is used by ``Clock_exit()``.
It should disable the clock tick source if it was enabled. This can be used to
prevent clock ticks after the system is shutdown.
@@ -261,12 +284,26 @@ prevent clock ticks after the system is shutdown.
}
#define Clock_driver_support_shutdown_hardware() \
- some_support_shutdown_hardware()
+ some_support_shutdown_hardware()
#include "../../../shared/clockdrv_shell.h"
+SMP Support
+===========
+
+In SMP configurations, the clock tick service must be executed for each
+processor used by RTEMS. By default, the clock tick interrupt must be
+distributed to all processors used by RTEMS and each processor invokes the
+clock tick service individually. A clock driver may delegate all the work to
+the boot processor. It must define ``CLOCK_DRIVER_USE_ONLY_BOOT_PROCESSOR`` in
+this case.
+
+Clock drivers must define
+``Clock_driver_support_set_interrupt_affinity(online_processors)`` to set the
+interrupt affinity of the clock tick interrupt.
+
Multiple Clock Driver Ticks Per Clock Tick
-------------------------------------------
+==========================================
In case the hardware needs more than one clock driver tick per clock tick (e.g.
due to a limited range of the hardware timer), then this can be specified with
@@ -285,7 +322,7 @@ x86 and it hopefully remains that way.
#include "../../../shared/clockdrv_shell.h"
Clock Driver Ticks Counter
---------------------------
+==========================
The :dfn:`Clock Driver Shell` provide a global variable that is simply a count
of the number of clock driver interrupt service routines that have occurred.