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.
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