--background-- 
     AbortIO() 
     AddTime() 
     CmpTime() 
     GetSysTime() 
     ReadEClock() 
     SubTime() 
     TR_ADDREQUEST 
     TR_GETSYSTIME 
     TR_SETSYSTIME 

   TIMER REQUEST
	A time request is a non standard IO Request.  It has an IORequest
	followed by a timeval structure or an eclockval structure.

   TIMEVAL
	A timeval structure consists of two longwords.  The first is
	the number of seconds, the latter is the fractional number
	of microseconds.  The microseconds must always be "normalized"
	e.g. the longword must be between 0 and one million.

   ECLOCKVAL
	A eclockval structure consists of two longwords.  The first is
	the high order 32 bits of a 64 bit number and the second is the
	the low order 32 bits.  The 64 bit number is a count of "E" clock
	ticks.  The "E" clock frequency is related to the master clock
	frequency of the machine and can be determined by calling the
	ReadEClock() library like call.

   UNITS
	The timer contains five units -- two designed to accuratly measure
	short intervals, one that has little system overhead and is very
	stable over time, and two that work like an alarm clock.

   UNIT_MICROHZ
	This unit uses the programmable timers in the 8520s to keep track
	of its time.  It has precision down to about 2 microseconds, but
	will drift as system load increases.  The accuracy of this unit
	is the same as that of the master clock of the machine.  This unit
	uses a timeval in its timerequest.

   UNIT_VBLANK
	This unit uses a strobe from the power supply to keep track of its
	time or the "E" clock on machines without power supply strobes.
	It is very stable over time, but only has a resolution of that of
	the vertical blank interrupt.  This unit is very cheap to use, and
	should be used by those who are waiting for long periods of time
	(typically 1/2 second or more).  This unit uses a timeval in its
	timerequest.

   UNIT_ECLOCK
	This unit is exacly the same as UNIT_MICROHZ except that it uses
	an eclockval instead of a timeval in its timerequest.

   UNIT_WAITUNTIL
	This unit waits until the systime is greater than or equal to the
	time in the timeval in the timerequest.  This unit has the same
	resolution and accuracy as that of UNIT_VBLANK.

   UNIT_WAITECLOCK
	This unit waits until the E-Clock value as returned by ReadEClock()
	is greater than or equal to the eclockval in the timerequest. This
	unit has the same resolution and accuracy as that of UNIT_ECLOCK.

   LIBRARY
	In addition to the normal device calls, the timer also supports
	several direct, library like calls.

   BUGS
	In the V1.2/V1.3 release, the timer device has problems with
	very short time requests.  When one of these is made, other
	timer requests may be finished inaccurately.  A side effect
	is that AmigaDOS requests such as "Delay(0);" or
	"WaitForChar(x,0);" are unreliable.

   NAME
	AbortIO -- Remove an existing timer request.

   SYNOPSIS
	error = AbortIO( timerequest )
	D0               A1

	LONG AbortIO( struct timerequest * );

   FUNCTION
	This is an exec.library call.

	This routine removes a timerquest from the timer.  It runs in
	the context of the caller.

   INPUTS
	timerequest - the timer request to be aborted

   RETURNS
	0  if the request was aborted, io_Error will also be set to
	    IOERR_ABORTED.
	-1 otherwise

   NOTES
	This function may be called from interrupts.

   SEE ALSO
	exec.library/AbortIO()

   BUGS

   NAME
	AddTime -- Add one time request to another.

   SYNOPSIS
	AddTime( Dest, Source )
	         A0    A1

	void AddTime( struct timeval *, struct timeval *);

   FUNCTION
	This routine adds one timeval structure to another.  The
	results are stored in the destination (Dest + Source -> Dest)

	A0 and A1 will be left unchanged

   INPUTS
	Dest, Source -- pointers to timeval structures.

   NOTES
	This function may be called from interrupts.

   SEE ALSO
	timer.device/CmpTime(),
	timer.device/SubTime()

   BUGS

   NAME
	CmpTime -- Compare two timeval structures.

   SYNOPSIS
	result = CmpTime( Dest, Source )
	D0                A0    A1

	LONG CmpTime( struct timeval *, struct timeval *);

   FUNCTION
	This routine compares timeval structures

	A0 and A1 will be left unchanged

   INPUTS
	Dest, Source -- pointers to timeval structures.

   RESULTS
	result will be   0 if Dest has same time as source
	                -1 if Dest has more time than source
	                +1 if Dest has less time than source

   NOTES
	This function may be called from interrupts.

   SEE ALSO
	timer.device/AddTime(),
	timer.device/SubTime()

   BUGS
	Older version of this document had the sense of the return
	codes wrong; the code hasn't changed but the document has.

   NAME
	GetSysTime -- Get the system time. (V36)

   SYNOPSIS
	GetSysTime( Dest )
	            A0

	void GetSysTime( struct timeval * );

   FUNCTION
	Ask the system what time it is.  The system time starts off at
	zero at power on, but may be initialized via the TR_SETSYSTIME
	timer.device command.

	System time is monotonocally increasing and guarenteed to be
	unique (except when the system time is set back).

	A0 will be left unchanged.

	This function is less expensive to use than the TR_GETSYSTIME
	IORequest.

   INPUTS
	Dest -- pointer to a timeval structure to hold the system time.

   RESULTS
	Dest -- the timeval structure will contain the system time.

   NOTES
	This function may be called from interrupts.

   SEE ALSO
	timer.device/TR_GETSYSTIME,
	timer.device/TR_SETSYSTIME,

   BUGS

   NAME
	ReadEClock -- Get the current value of the E-Clock. (V36)

   SYNOPSIS
	E_Freq = ReadEClock( Dest )
	D0                   A0

	ULONG ReadEClock ( struct EClockVal * );

   FUNCTION
	This routine calculates the current 64 bit value of the E-Clock
	and stores it in the destination EClockVal structure. The count
	rate of the E-Clock is also returned.

	A0 will be left unchanged

	This is a low overhead function designed so that very short
	intervals may be timed.

   INPUTS
	Dest -- pointer to an EClockVal structure.

   RETURNS
	Dest -- the EClockVal structure will contain the E-Clock time
	E_Freq -- The count rate of the E-Clock (tics/sec).

   NOTES
	This function may be called from interrupts.

   SEE ALSO

   BUGS

   NAME
	SubTime -- Subtract one time request from another.

   SYNOPSIS
	SubTime( Dest, Source )
	         A0    A1

	void SubTime( struct timeval *, struct timeval *);

   FUNCTION
	This routine subtracts one timeval structure from another.  The
	results are stored in the destination (Dest - Source -> Dest)

	A0 and A1 will be left unchanged

   INPUTS
	Dest, Source -- pointers to timeval structures.

   NOTES
	This function may be called from interrupts.

   SEE ALSO
	timer.device/AddTime(),
	timer.device/CmpTime()

   BUGS

   NAME
	TR_ADDREQUEST -- Submit a request to wait a period of time.

   FUNCTION
	Ask the timer to wait a specified amount of time before
	replying the timerequest.

	The message may be forced to finish early with an
	AbortIO()/WaitIO() pair.

   TIMER REQUEST
	io_Message      mn_ReplyPort initialized
	io_Device       preset by timer in OpenDevice
	io_Unit         preset by timer in OpenDevice
	io_Command      TR_ADDREQUEST
	io_Flags        IOF_QUICK permitted (but ignored)
	tr_time         a timeval structure specifying how long the 
	                    device will wait before replying

   RESULTS
	tr_time         will be zeroed

   NOTES
	This function may be called from interrupts.

	Previous to 2.0, the tr_time field was documented as containing
	junk when the timerequest was returned.

   SEE ALSO
	timer.device/AbortIO(),
	timer.device/TimeDelay(),

   BUGS

   NAME
	TR_GETSYSTIME -- get the system time.

   FUNCTION
	Ask the system what time it is.  The system time starts off at
	zero at power on, but may be initialized via the TR_SETSYSTIME
	call.

	System time is monotonically increasing, and guaranteed to be
	unique (except when the system time is set backwards).

   TIMER REQUEST
	io_Message      mn_ReplyPort initialized
	io_Device       preset by timer in OpenDevice
	io_Unit         preset by timer in OpenDevice
	io_Command      TR_GETSYSTIME
	io_Flags        IOF_QUICK permitted

   RESULTS
	tr_time         a timeval structure with the current system
	                    time

   NOTES
	This function may be called from interrupts.

   SEE ALSO
	timer.device/TR_SETSYSTIME,
	timer.device/GetSysTime(),

   BUGS

   NAME
	TR_SETSYSTIME -- Set the system time.

   FUNCTION
	Set the system idea of what time it is.  The system starts out
	at time "zero" so it is safe to set it forward to the real
	time.  However, care should be taken when setting the time
	backwards.  System time is generally expected to monotonically
	increasing.

   TIMER REQUEST
	io_Message      mn_ReplyPort initialized
	io_Device       preset by timer in OpenDevice
	io_Unit         preset by timer in OpenDevice
	io_Command      TR_GETSYSTIME
	io_Flags        IOF_QUICK permitted
	tr_time         a timeval structure with the current system
	                    time

   RESULTS
	tr_time         will contain junk

   NOTES
	This function may be called from interrupts.

   SEE ALSO
	timer.device/TR_GETSYSTIME,
	timer.device/GetSysTime(),

   BUGS