RX02 Bootstrap

From: Andreas Freiherr <Andreas.Freiherr_at_Vishay.com>
Date: Thu Feb 28 13:24:11 2002

Ben,

let me continue to be picky, as I often learn new things by trying to
really and thoroughly understand how something works. ;-)

> > > > Let me continue, and we can open a contest for writing the shortest
> > > > bootstrap! ;-)
> > >
> > > Hardware ... Reset button :)
> >
> > ... and then what...??? :-)
>
> Picky ...
> Well reset clear's the track,sector,head and DMA address registers.
> Clears the cpu's PC and sets the halt F/F and clears IRQ F/F.
> Then you jam 'read sector' into the disk controler. The DISK_DONE Irq
> clears
> the halt F/F.

Will work for some, but not all, media. RL01/RL02, for example, can be
done this way. I have seen a four-word bootstrap that indeed only
consists of putting the required command into the CSR and then WAITing.
Operating instructions: "let the program run for a few seconds, then
HALT and restart at address zero."

Will the IRQ really clear the halt F/F, causing the processor to resume
running? - I need to get my machines running soon, memory is fading...

Other disk types, such as the RXs, require loading of more than one
sector, and not many controllers are like the RK11 in that they
automatically increment sector counters.

What I wanted to point out is that you need to have some kind of
"handler" for the reset button if you want your PDP-11 to have a life
after that. I might call this "handler" a "bootstrap" :-) - And I
intended to have a PDP-11 processor execute the instructions, not a
human! ;-)

--
Andreas Freiherr
Vishay Semiconductor GmbH, Heilbronn, Germany
http://www.vishay.com
Received on Thu Feb 28 2002 - 13:24:11 GMT

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