@c
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@c
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@c COPYRIGHT (c) 1988-2002.
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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 On-Line Applications Research Corporation (OAR).
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@c All rights reserved.
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@c All rights reserved.
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@c
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@c
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@c clock.t,v 1.9 2002/01/17 21:47:44 joel Exp
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@c clock.t,v 1.9 2002/01/17 21:47:44 joel Exp
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@c
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@c
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@chapter Clock Driver
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@chapter Clock Driver
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@section Introduction
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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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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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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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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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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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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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@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 section describes the global variables expected to be provided by
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this driver.
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this driver.
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@subsection Major and Minor Number
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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 major and minor numbers of the clock driver are made available via
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the following variables.
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the following variables.
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@itemize @bullet
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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_major_number rtems_clock_major;
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@item rtems_device_minor_number rtems_clock_minor;
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@item rtems_device_minor_number rtems_clock_minor;
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@end itemize
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@end itemize
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The clock device driver is responsible for declaring and
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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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initializing these variables. These variables are used
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by other RTEMS components -- notably the Shared Memory Driver.
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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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@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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with the clock device driver registering @b{/dev/clock}.
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@subsection Ticks Counter
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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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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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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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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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a system. This variable is declared as follows:
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@example
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@example
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volatile rtems_unsigned32 Clock_driver_ticks;
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volatile rtems_unsigned32 Clock_driver_ticks;
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@end example
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@end example
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@section Initialization
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@section Initialization
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The initialization routine is responsible for
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The initialization routine is responsible for
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programming the hardware that will periodically
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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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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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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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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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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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@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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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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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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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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your clock interrupt service routine:
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@example
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@example
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rtems_interrupt_catch (Clock_ISR, CLOCK_VECTOR, &old_handler);
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rtems_interrupt_catch (Clock_ISR, CLOCK_VECTOR, &old_handler);
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@end example
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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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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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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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to schedule their @code{Clock_exit} routine to execute when the
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system is shutdown.
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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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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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tick if the @code{ticks_per_timeslice} field of the Configuration
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Table is 0.
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Table is 0.
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@section System shutdown
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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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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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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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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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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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system is shutdown.
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@section Clock Interrupt Subroutine
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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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It only has to inform the kernel that a ticker has elapsed, so call :
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@example
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@example
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@group
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@group
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rtems_isr Clock_isr( rtems_vector_number vector )
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rtems_isr Clock_isr( rtems_vector_number vector )
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@{
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@{
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invoke the rtems_clock_tick() directive to announce the tick
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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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if necessary for this hardware
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reload the programmable timer
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reload the programmable timer
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@}
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@}
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@end group
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@end group
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@end example
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@end example
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@section IO Control
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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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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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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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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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service routine. The following shows the functionality required:
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@example
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@example
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@group
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@group
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rtems_device_driver Clock_control(
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rtems_device_driver Clock_control(
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rtems_device_major_number major,
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rtems_device_major_number major,
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rtems_device_minor_number minor,
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rtems_device_minor_number minor,
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void *pargp
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void *pargp
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)
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)
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@{
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@{
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error check the argument pointer parameter
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error check the argument pointer parameter
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if the command is "ISR"
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if the command is "ISR"
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invoke the clock interrupt service routine
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invoke the clock interrupt service routine
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else if the command is "NEW"
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else if the command is "NEW"
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install the requested handler
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install the requested handler
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@}
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@}
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@end group
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@end group
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@end example
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@end example
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