Extremely CISC instructions

[Tony Duell]

On Wed, Aug 25, 2021 at 7:07 PM ben via cctalk <cctalk at classiccmp.org> wrote:
>
> On 2021-08-25 11:08 a.m., Josh Dersch via cctalk wrote:
>
> > (The Three Rivers PERQ included a similar "RASTEROP" instruction in its

Well, it might do.There is no requirement for the PERQ machine code
instruction set to include that, or any other particular instruction.

The PERQ loads its microcode from disk when it boots. The hardware
that the microcode runs on is pretty much RISC, for example all but
one class of instruction [1] execute in one microcycle. You can have
just about any machine code instruction defined in the microcode, yuu
could have the CRC or POLY instructions if you wanted them. I remember
a 'competiton' some years back for the shortest machine code ROT13
encoder/decoder, somebody submitted a 1-instruction solution for the
ERQ, the catch being tht of course it needed an extra bit of mcrocode
to implement that instruction.

[1] Those being the instructions that load the microcode control
store. These take 2 microcycles.

> > repertoire, which was similar to BITBLT but also allowed for various
> > logical operations to be applied to the source and destination.)

That was pretty much done in the hardware (the 'combiner PROMs'). The
microcode handled generating the memory addresses and starting the
appropriate overlapped memory cycles, the hardware aligned the words
(barrel shifter) and combined them with the appropriate logical
operation.

>
> All rendered useless if you move to gray or color. Sadly almost
> all monitors are landscape rather than portrait, so we may never see
> a good emulation of them.

Most PERQ2T2s were actually landscape (1280*1024 pixels)

But I'l skip the emulation. After all there are 3 classic PERQs and an
AGW3300 rather close to me here...

-tony