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* SUPPORT, LICENSE: New files. * Numerous files touched as part of merging the 4.5 branch onto the mainline development trunk and ensuring that the script that cuts snapshots and releases works on the documentation.
133 lines
3.9 KiB
Perl
133 lines
3.9 KiB
Perl
@c
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@c COPYRIGHT (c) 1988-2002.
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@c On-Line Applications Research Corporation (OAR).
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@c All rights reserved.
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@c
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@c $Id$
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@c
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@chapter Clock Driver
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@section Introduction
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The purpose of the clock driver is to provide a steady time
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basis to the kernel, so that the RTEMS primitives that need
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a clock tick work properly. See the @code{Clock Manager} chapter
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of the @b{RTEMS Application C User's Guide} for more details.
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The clock driver is located in the @code{clock} directory of the BSP.
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@section Clock Driver Global Variables
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This section describes the global variables expected to be provided by
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this driver.
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@subsection Major and Minor Number
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The major and minor numbers of the clock driver are made available via
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the following variables.
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@itemize @bullet
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@item rtems_device_major_number rtems_clock_major;
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@item rtems_device_minor_number rtems_clock_minor;
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@end itemize
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The clock device driver is responsible for declaring and
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initializing these variables. These variables are used
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by other RTEMS components -- notably the Shared Memory Driver.
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@b{NOTE:} In a future RTEMS version, these variables may be replaced
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with the clock device driver registering @b{/dev/clock}.
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@subsection Ticks Counter
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Most of the clock device drivers provide a global variable
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that is simply a count of the number of clock driver interrupt service
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routines that have occured. This information is valuable when debugging
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a system. This variable is declared as follows:
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@example
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volatile rtems_unsigned32 Clock_driver_ticks;
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@end example
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@section Initialization
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The initialization routine is responsible for
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programming the hardware that will periodically
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generate an interrupt. A programmable interval timer is commonly
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used as the source of the clock tick.
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The device should be programmed such that an interrupt is generated
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every @i{m} microseconds, where @i{m} is equal to
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@code{BSP_Configuration.microseconds_per_tick}. Sometimes the periodic interval
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timer can use a prescaler so you have to look carefully at your user's
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manual to determine the correct value.
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You must use the RTEMS primitive @code{rtems_interrupt_catch} to install
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your clock interrupt service routine:
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@example
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rtems_interrupt_catch (Clock_ISR, CLOCK_VECTOR, &old_handler);
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@end example
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Since there is currently not a driver entry point invoked at system
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shutdown, many clock device drivers use the @code{atexit} routine
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to schedule their @code{Clock_exit} routine to execute when the
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system is shutdown.
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By convention, many of the clock drivers do not install the clock
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tick if the @code{ticks_per_timeslice} field of the Configuration
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Table is 0.
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@section System shutdown
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Many drivers provide the routine @code{Clock_exit} that is scheduled
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to be run during system shutdown via the @code{atexit} routine.
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The @code{Clock_exit} routine will disable the clock tick source
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if it was enabled. This can be used to prevent clock ticks after the
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system is shutdown.
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@section Clock Interrupt Subroutine
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It only has to inform the kernel that a ticker has elapsed, so call :
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@example
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@group
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rtems_isr Clock_isr( rtems_vector_number vector )
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@{
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invoke the rtems_clock_tick() directive to announce the tick
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if necessary for this hardware
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reload the programmable timer
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@}
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@end group
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@end example
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@section IO Control
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The clock driver must supply a handler for the IO control device driver
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entry point. This functionality is used by other components -- notably
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the Shared Memory Driver to install a wrapper for the clock interrupt
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service routine. The following shows the functionality required:
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@example
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@group
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rtems_device_driver Clock_control(
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rtems_device_major_number major,
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rtems_device_minor_number minor,
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void *pargp
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)
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@{
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error check the argument pointer parameter
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if the command is "ISR"
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invoke the clock interrupt service routine
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else if the command is "NEW"
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install the requested handler
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@}
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@end group
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@end example
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