Read Timer (RDT)/OP=95


OP AF BF A Syllable

OP = 95

AF is the processor selection field. May be specified as an indirect field length. A literal flag will cause an Invalid Instruction (IEX = 21) fault.

BF is the variant and may be specified as an indirect field length. The following variants may be specified:

BF Description
00 Read Time of Day Timer
01 Read and Clear Processor Timers

A is the address of the memory location where the timer information is to be stored. Address may be indexed, indirect or extended. The final address controller must equal UN or cause an Invalid Instruction (IEX = 03) fault.


The Read Timer instruction is used to retrieve the current Time-Of-Day timer or the processor timers from the specified processor.

BF = 00 Read Time of Day Timer

The Read Time of Day Timer instruction will store the twenty digit Time of Day Timer at the memory location specified by the A address.

BF = 01 Read And Clear Processor Timers

The Read and Clear processor timers instruction will store the following accumulated processor times for the processor specified by the AF field at the memory location specified by the A address. Then the processor timers are reset to zero. The resolution of the processor timers is in microseconds. See Compatibility Notes A.36.

Information Digits
IDLE Mode Time 00 - 11
KERNEL Mode Time 12 - 23
INTERRUPTING Mode Time 24 - 35

This variant of the Read Timer instruction may only be executed with Privileged Enable set, or an Invalid Instruction (IEX = 02) fault is reported.

Detailed Description
  1. If the AF value equals “00”, then the processor times are for the current processor. Otherwise, the AF value contains the processor number of the processor for which the processor times are to be reported. However, if the processor number is greater than the allowable processors, the Overflow flag is set and the instruction terminates without further action.
  2. The processor timers for the selected processor are stored according to the above format in memory starting at the location specified by the resolved A address.
  3. The internal processor timers for these processor times are then reset to zero.

Note that these accumulated processor times are update by a processor upon entry into and/or exit from KERNEL Mode. As a result, the accumulated times for a processor not currently in KERNEL mode are only up-to-date as of the last time that processor was in KERNEL mode. In order to get completely up-to-date processor times it is therefore recommended that this instruction only be executed for a processor while that processor is in KERNEL mode.

Comparison and Overflow Flags

The Overflow Flag is set if the processor number specified in AF is greater than the number of allowable processors (BF=01). Otherwise the overflow flag is reset.

The Comparison Flags are not affected by this instruction.


Field overlap is not applicable to this instruction.


OP AF BF A Syllable
95 00 00 A Field UN
                    BEFORE                AFTER
  A FIELD           nnnnnnnnnnnnnnnnnnnn  20170627001234567890
  COMPARISON          nn                  unchanged
  OVERFLOW            nn                  0
instructions/rdt.txt · Last modified: 2017/06/27 11:15 by scott
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