[Info-vax] Y3K for PDP-11 Operating Systems

[Johnny Billquist]

On 2011-05-10 11.45, Bob Koehler wrote:
> In article<iqbllp$u0i$1 at Iltempo.Update.UU.SE>, Johnny Billquist<bqt at softjar.se>  writes:
>>
>> I'm pretty sure that on later machines, MOVTUC is an emulated
>> instruction, so you don't want to use it unless you really want the
>> special features. For the simple C string case, having that translation
>> table is a small memory cost, but it also hurts performance.
>> But from a purity point of view, yes, MOVTUC should also be able to do it.
>
>     IIRC, LOCC and MOVCx are in the same VAX instruction subset as
>     MOVTUC.  And the rules were you can do all of a subset in hardware,
>     or none of the subset in hardware, but you couldn't break it up.
>
>     For example, IIRC, MV II did none of the string instructions in
>     hardware.

The MVII don't follow later rules about what to emulate and what to do 
in hardware. Those rules came later, and perhaps partly as an analysis 
after the MVII. As such, the MVII do not have LOCC in hardware, nor 
CMPCx, or a bunch of other string instructions that are "now" required. 
But it does have some other instructions that are very optional.

But actually, MOVTUC is in the group of instructions never required to 
be implemented, and which can be handpicked one by one, so it's not even 
in a group of instructions.

MOVCx and LOCC on the other hand are in the required group of 
instructions. So they are not even optional.

(Check chapter 11 of the VARM (DEC STD 032))

	Johnny