PDP 11/45 light chaser

[Paul Koning]

>>>>> "Gooijen" == Gooijen H <Gooijen> writes:

 Gooijen> RE: PDP 11/45 light chaser
>>>>> "Gooijen" == Gooijen H <Gooijen> writes:

 Gooijen> The drawback of the light chaser program that uses the RESET
 Gooijen> instruction is that the heads load and unload of the RX02
 Gooijen> drive in my PDP-11/40.  That clunck-clunck sound is not
 Gooijen> pretty for a longer while ...

 >> So start up the KW11L clock, point its vector to an RTI, and use a
 >> WAIT instead of a RESET...
 >> 
 >> paul

 Gooijen> Hmm, I thought that the RESET instruction provides the ~100
 Gooijen> ms delay so that the lights are visible (on the 11/35 they
 Gooijen> are LEDs anyway) but this instruction also asserts the
 Gooijen> RESET/ (BUS INIT-L ?) signal.  That is what makes the RX
 Gooijen> drive clunk - at least that's what I thought.

Exactly right.  That's why I suggested WAIT -- it will pause until the
next interrupt, and leave the INIT line alone.  WAIT, of course, is
what you'd find in the idle loop in a real OS:

NULJOB:	MOV	R2,R1		; Reset delay counter
10$:	WAIT			; Now wait...
	SOB	R1,10$		;  for specified delay
	ROL	R0		; Shift the lights
	BR	NULJOB		;  and continue

     paul