Lisp, the machine language. Was Re: Hallelujah!

From: Buck Savage <hhacker_at_home.com>
Date: Sun Apr 4 16:57:32 1999

>> "Buck Savage" <hhacker_at_home.com> wrote:
>> > Actually, microcode is not compiled.
>>
>> All the microcode I've ever written was compiled. Of course, it was
>> compiled from special source languages defined for that explicit purpose.
>> No one with any sense would write a non-trivial amount of microcode any
>> other way.
>
>All the microcode I've ever written (or seen) was written in a special
>_assembly_ language. Or at least I'd class it as that as (a) one 'line'
>of microcode corresponded to one microinstruction and (b) the language
>statements were pretty close to the hardware definition.
>
>Here's a PERQ microinstruction :
>
>R0:=R0+R1, if neq goto(loop);
>
>The first 'phrase' defines the contents of
>X and Y fields (select particular registers)
>AMUX, BMUX fields (gate registers to ALU inputs, rather than, say gating
>a constant there)
>ALU field (do an addition operation)
>W field (we want to write it back to a register and not just set the flags)
>
>The second phrase sets the
>Condition field (to select the 'not equal' condition)
>Jump field (to do a got and not just a next instruction, say)
>SF and Z fields (to define the jump address).
>
>So the actual machine instruction is pretty close to the higher level
>version. OK, some fields (Z in particular) can be set by several
>different types of phrase, as the Z field is used for jump addresses and
>IO addresses and shifter control and constants and... Yes the assembler
>moans if you try to set it in 2 different ways in the same instruction.
>
>-tony
>

This is my experience as well. HP 21MX microcode is very similar. I will
dig up some examples and post it at a later time.

Thanks, Tony, for the examples and the clarification.

William R. Buckley
Received on Sun Apr 04 1999 - 16:57:32 BST