mikpe.pdp10-tools/doc/Timers.txt

doc/Timers.txt
Copyright (C) 2015-2017  Mikael Pettersson

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PDP10 Timers
============

PDP6 / KA10 / KI10
------------------

- there is a clock tied to the AC power line frequency (50 or 60 Hz)
- the clock is part of the "processor conditions"
- CONO APR,E allows the clock interrupt to be enabled or disabled, and the entire group
  of processor conditions to be assigned an interrupt priority level
- on KI10, the clock has its own interrupt priority level assignment
- on PDP6 and KA10, the clock shares interrupt priority level with the other processor conditions
- CONI APR,E allows the current state of the processor conditions to be inspected
- KI10 also has a "timer", but it functions like a watchdog and is not usable as a clock

KL10
----

- 1 MHz time base, recorded in two words in the EPT
- 12-bit 100 kHz interval timer able to raise interrupts with programmable period
- CONO MTR,E assigns interrupt level to the interval timer, and enables or disables the time base
- CONO TIM,E assigns interrupt period to the interval timer, and enables or disables it
- CONI TIM,E reads the current contents of the interval timer, as well as its configuration data
- KL10 also has a "metering" system, similar to programmable performance monitoring counters

KS10/KD10
---------

- a 12-bit hardware millisecond counter, running at 4.1 MHz, overflow represents just under 1 ms
- a "time base" doubleword (36+35 bits) in "the workspace", with the low 12 bits corresponding
  to the hardware counter
- an "interval" word in "the workspace" able to represent intervals up to 2^23 ms (almost 140 minutes)
- WRTIM writes a doubleword to the time base (clearing the low 12 bits)
- RDTIM reads the time base, adds the hardware counter, and writes a doubleword
- WRINT writes a word to the interval register
- RDINT reads the interval register and writes a word
- WRAPR allows the interval done interrupt to be enabled, if so it shares priority level with
  several other "system conditions"

Jupiter/KC10
------------

- 12-bit 100 kHz interval timer able to raise interrupts with programmable period, identical to KL10
- WRTMB E similar to KL10 CONO MTR,E
- WRINT E equivalent to KL10 CONO TIM,E
- RDINT E equivalent to KL10 CONI TIM,E
- doubleword timebase, updated via a 16 bits 1usec hardware counter

XKL-1 / Toad-1
--------------

- interval timer: 8-bit hardware counter incremented every 128 usec, on overflow signals interrupt and
  reloads the interval (between 1 and 127, inclusive)
- WRITM E loads a new interval, assigns priority level, and optionally clears the timer
- interrupt vectors via an emulated XPCW using locations 100-103 in the EPT
- RDITM E reads the state of the timer (except for its current count)

- time base: a 60-bit count updated via a 16 bit 500 ns (2 MHz) hardware counter
- RDTIME E reads the time base as a doubleword
- WRTIME E writes a doubleword to the time base, except for the bits corresponding to the hardware counter
- looks Jupiter-like

- watchdog: a hardware decrementer with 32.8 millisecond intervals, except when the processor is halted
  or the watchdog is disabled (via WCTRLF E)
- WRKPA Y writes 18-bit immediate to the decrementer
- if the decrementer reaches zero, it signals a "keep-alive" interrupt which is very much like an NMI