[LMH] Re: [LMH]CADR software/images?

Sat, 28 Aug 2004 12:36:32 -0500

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Brad Parker wrote:<br>
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 cite="mid200408272128.i7RLSPvV007461@mwave.heeltoe.com">
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I'm enjoying the notion of sucking the CADR netlist files into a modern
synthesis tool and using one of the cheap FPGA w/sdram eval boards to
fire up nuevo-cadr.  There's certainly enough ram in most modern parts
to hold all the microcode.  It's a sick idea but a fun one...

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<span style="font-family: monospace;">I'd be surprised if that would
work at all.&nbsp; The CADR has an interesting clocking scheme that is
"mostly synchronous".&nbsp; The main clock generation is by means of a pulse
delay line.&nbsp; The period is controlled by the type of the
microinstruction, which is used to select a tap for recycling the
pulse.&nbsp; Some microinstructions (DISPATCH) run slower than others.&nbsp;
Furthermore, the machine goes asynchronous when performing a memory
cycle.&nbsp; The clock stops completely in the processor once a memory
request has gone onto the bus.&nbsp; If you follow the memory ACK through
the schematics, it actually forms the pulse that goes back into the
delay line to clock the next cycle.<br>
<br>
All of that can be sorted out, but not be any automatic tool.<br>
<br>
All in all, the CADR processor architecture is unlike modern designs in
a lot of ways that are likely to result in poor automatic synthesis.<br>
<br>
I think the more interesting project would be a CADR-compatible design
in a modern style.&nbsp; It would use more pipelining and maybe larger
memory maps.&nbsp; It would have to run CADR microcode unchanged.&nbsp; It would
need to have all of the compatible peripherals so that the microcode
could access them.<br>
<br>
This discussion reminds me, I had started to write a description of
(some of the arcane aspects of) the CADR and how it was morphed into
Explorer I and Explorer II.&nbsp; I'll have to find that.&nbsp; Oh, and _that_
reminds me that I promised to let the the ex-AI Lab and LMI guys I ran
into this summer in Cambridge take a look at it for accurracy and
expansion.&nbsp; I guess I'd better get busy.<br>
<br>
&nbsp;&nbsp;&nbsp; -Steve<br>
<br>
<br>
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