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119 lines
4.4 KiB
Plaintext
119 lines
4.4 KiB
Plaintext
/* DVHOST.TXT - The special HOST device
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*/
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/* $Id: dvhost.txt,v 2.3 2001/11/10 21:24:21 klh Exp $
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*/
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/* Copyright © 1997-1999, 2001 Kenneth L. Harrenstien
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** All Rights Reserved
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**
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** This file is part of the KLH10 Distribution. Use, modification, and
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** re-distribution is permitted subject to the terms in the file
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** named "LICENSE", which contains the full text of the legal notices
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** and should always accompany this Distribution.
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*/
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THE "HOST" DEVICE
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This is not a real device, nor is it anything that ever
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existed on a real PDP-10. Rather, it is a pseudo-device which serves
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as a simple API to request services or information from the emulator.
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It is called "HOST" to emphasize that its status or I/O represents
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communication with the native host platform that the emulator is
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running on.
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"HOST" DEVICE CONFIGURATION
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As for other devices, the DEVDEFINE command must be used
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(typically as a line in "klh10.ini") to associate the HOST device with
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either a unibus address (for the KS10) or a PDP-10 device number (for
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all other models). This needs to be a device number or address that
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is not otherwise used by something else, and any monitor modifications
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that refer to this device must use the same number or address.
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KL10 example:
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devdefine idler 700 host ; PDP-10 device 700
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where "host" specifies the HOST device; "idler" is a name
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of your own choosing, and 700 is simply a device number that
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does not conflict with any standard DEC devices.
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KS10 example:
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devdef idler ub3 host addr=777000
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where "host" specifies the HOST device; "idler" is a name
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of your own choosing, and "ub3" plus "addr=777000" specifies
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a unibus address that should not conflict with any standard
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DEC devices.
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There are currently no configuration parameters associated with the HOST
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device, and only one such device can be defined.
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KL10 "HOST" DEVICE USAGE
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Although any of the four basic PDP-10 I/O instructions (CONI,
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CONO, DATAI, DATAO) can be used with this device, only one specific
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instance is currently meaningful, and its use is very simple.
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IDLE FUNCTION: CONO <hstdev>,1
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The emulator process will enter an "idle" state with respect to the
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host system, until a PI (priority interrupt) event occurs. During
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this state no host CPU time is consumed emulating PDP-10 instructions,
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although device subprocesses are still free to run. Instruction
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execution will resume with a dispatch to the appropriate PI
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interrupt handler, which should eventually return to the next
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instruction following the CONO.
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All other I/O instructions will behave as if the device was
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non-existent. A CONO with an E != 1 will be a no-op, as will DATAO;
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CONI and DATAI simply read a zero word. However, new functions can
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obviously be readily added as the need arises.
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KS10 "HOST" DEVICE USAGE
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To invoke the "idle function" on the KS10, just write the
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value "1" to the device's unibus address. The exact IO instruction
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used to do this should not matter.
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MONITOR PATCHES FOR THE "IDLE" FUNCTION:
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In order to effectively use the HOST "idle" function, you must
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determine the right place to patch your monitor to use it -- the point
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in the scheduler where the system decides there isn't anything it can
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do and begins to run the "null job".
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For a TOPS-20 V7 monitor the most appropriate patch is to replace the
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instruction at SCDNL1-1 in SCHED.MAC (a JRST SCDNL2) with the "IDLE"
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function instruction. In context:
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SCDNUL: SETOM NULJBF
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SCDNL2: ...
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<null job stuff>
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JRST SCDNL1 ; Something to do.
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JRST SCDNL2 ; Replace with CONO <hstdev>,1
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; which will fall through when there's
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; any PI activity.
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SCDNL1: <start of sched cycle>
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...
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For a TOPS-10 monitor I would suggest replacing the instruction at
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NULCOD+1 in CLOCK1.MAC (a SOJG 6,1) with the "IDLE" function
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instruction. However, this has not been well tested and there may be
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a more appropriate place.
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You can verify whether this function is working by observing the
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process CPU usage on the host system. As long as the KN10 is not
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running the monitor's null job, the emulator will be using as much CPU
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time as possible -- as much as 95% on an otherwise lightly loaded
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single-CPU system. But when the monitor has nothing to run and the
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KN10 is effectively idle, the emulator's CPU usage should drop to
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perhaps 5%. It will never be completely zero because all monitors
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always maintain a clock interrupt that drives periodic updates and
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scheduler checks.
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