🚀 go-pugleaf

In <1989Jan26.210550.10129@gpu.utcs.toronto.edu> Bard Fowles (anakin@gpu.utcs.
.toronto.edu) dares to write:

>        Oops! I'm afraid I don't pull *BERR if the Coprocessor ain't there.
>Does anyone else. Boy ya learn something new every day. I must admit that
>this makes perfect sense, Dale. Atleast his machine would GURU instead of
>going off to la-la land. I humbly appologise.
>
>                                        Brad
>
>BTW Valentin, does the board work now with the 881 installed?

Like a charm! Even at 20Mhz with an Insider board under it. Due to the
Insider's clock, the Lucas board gets to ride very high, so I can't put the
RF shield back properly, but then who cares about the neighbor's TV reception?
You know, I lost a month of my life on the missing 68881 problem. I still can't
believe I did not realize what was going on when I noticed that *SENSE was
unconnected.

For people who can't afford to buy a 68881, I think that straightening out
horizontally pin 18 on PAL U4 (*CPCS) and wire wrapping the socket's pin to
Vcc through an unused SIP resistor should do the trick. Thus *CPCS will never
get asserted, and the CPU space address will be handled by the rest of the
Amiga. If the address is way off, a *BERR signal will be asserted. Otherwise
some erroneous data will be fed to the CPU.

If this trick does not work, then I could post a Kickstart patch to take away
the problematic 68881 instructions. Patching Kickstart without the hardware
hack would work too, but the Amiga would then hang whenever the CPU encounters
an F-line instruction.

Another solution is for you to redesign the Lucas board and use the *SELECT
pin provided on the 68881.  :-)  That would also give you the opportunity to
fix the U9 problem and maybe add a 68851 socket. (Oh please, oh please)

Now a small question about the Lucas design. Could you not have connected the
DSACK0/DSACK1 pins of the 68881 directly to the 68020 like I see it done on
all Motorola manuals I have, instead of ORing them through your PALs? These
two pins are automatically put into high impedance mode by the 68881 when they
are not used by it.

Valentin

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"An  operating  system  without         Name: Valentin Pepelea
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