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A time request is a non standard IO Request. It has an IORequest
followed by a timeval structure or an eclockval structure.
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.
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.
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.
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.
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
This unit is exacly the same as UNIT_MICROHZ except that it uses
an eclockval instead of a timeval in its timerequest.
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.
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.
In addition to the normal device calls, the timer also supports
several direct, library like calls.
In the V1.2/V1.3 release, the timer device has problems with
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