Cray CRAY-1 - Page 195

PROGRAMMABLE CLOCK OPTION
Cray Research provides as a standard option a programmable clock thay may
be used tc ~easure tile duration of intervals accurately. A periodic inter-
I rupt can be generated with intervals selected under monitor program control.
The clock frequency ;s 80 Mhz. Intervals from 12.5 nanoseconds to
53.7 seconds are
possible; however, intervals shorter than about 100
microseconds are not practical due to the monitor overhead involved in
processing the
interrupt.
INSTRUCTIONS
Provided with the clock are four additional instructions made possible by
redefining the k designator for the 0014 instruction. The option also
makes available two additonal registers: the interrupt interval register
(II) and the interrupt countdown counter (ICD).
0014j4
0014j5
0014j6
0014j7
Enter interrupt interval (II) register with (Sj)
Clear
the programmable clock interrupt request
Enable the
programmable clock interrupt request
Disable the
programmable clock interrupt requests
INTERRUPT INTERVAL REGISTER
The interrupt interval (II) register is a 32-bit register that can be
loaded with a binary value equal to the number of clock periods that are
to elapse
between programmable clock interrupt requests. The interrupt
interval is transferred from the lower 32 bits of the Sj register into
both the interrupt interval register and the interrupt countdown (ICD)
counter when the 0014j4 instruction is executed. This interval value is
held in the register and repeatedly sampled by the interrupt countdown
counter until another 0014j4 instruction is received to change the interval
value.
2240004
6-23
E-01