[LMH]Raven Microcode Questions

[Steve Krueger]

Alastair,

I'm sorry I've been slow to answer.

I can indeed answer almost any question on the Explorer I microcode engine.

Nyef wrote:

>Hello all.
>
>Over the past couple weeks I've been working on figuring out how the 
>Raven (Explorer I) processor interprets it's microcode. I've got some of 
>it figured out, but I have a few questions.
>
>I'm figuring that the condition field of the jump instruction 
>selectively disables the main jump action, in favor of the abbrev-jump 
>field action (if specified).
>

You are right.  If the condition is true, the jump action specified by 
R, P and N bits is performed.  If false, the  jump action of the 
abbreviated jump field is performed.  Only 000 (And-Nop), 110 (And-Popj) 
and 111 (And-Popj-Xct-Next) are allowed in the abbreviated jump field of 
a jump or dispatch microinstruction.

>
>My first question is how do the condition and abbrev-jump fields 
>interact on alu and byte instructions? How does the condition field 
>operate on these instructions without the abbrev-jump field?
>
The abbreviated jump field is conditioned on the condition selected by 
the condition field.  Like:

    (And-Call-Illop If-Not-Tag-Equal (M-T) M+1 M-T A-R)

This does unary arithmetic on M-T while checking that the tag of M-T is 
equal to the tag of A-R).

>
>My second question is what is the encoding for where to store the data 
>when using the jump instruction to read I-Memory?
>
Ah, that one I'll have to look up.

The M-bus source is written to I<31:00>.  The A-bus source bits <23:00> 
are written to I<55:32>.

The write sequence must be:

(Call-Xct-Next write-target)
   (Popj-Inhibit-Xct-Next A-Reg1 M-Reg2 WRITE-IRAM)

This writes into the I-Ram at write-target with I<55:32> coming from 
A-Reg1<23:00> and I<31:00> coming from M-Reg2<31:00>.

>
>I'm sure there are more questions waiting in the wings. Oh well.
>
>If someone could shed some light on these subjects it would be much 
>appreciated.
>
Again, sorry it took me so long.

    -Steve