Re: Creating several types from a base type and conversion

[Ken Roberts <alisonken1@gmail.com>]

On Friday, January 24, 2020 at 7:22:10 AM UTC-8, Simon Wright wrote:
> Ken Roberts <snip> writes:
> 
> > Based upon the hardware I worked on (and documentation for the 642
> > system), apparently it's BE based:
> >
> > Register representation on panel: R bits 29 .. 0
> >
> > where MSB is on the left and LSB on the right.
> 
> Looks LE to me.
> 
> If the panel shows
> 
> bit #   ...  5 4 3 2 1 0
> lit     ...  0 0 0 1 0 1
> 
> and the value represented is 5 then it's little-endian; bit 0 is the
> least significant bit.

My concern would be in bit shifting operations, that if a bit is shifted left 20 bits then:

start: 000000000000000000000000000001

end  : 000000000100000000000000000000

In one instruction for the 642, it combines two registers to make one 60-bit register for some operations, so representing both 30-bit and 60-bit register operations should be the same (assuming a 32-bit computer that should have both 32-bit and 64-bit operations).

At least that's what will have to be accomplished in the emulation.

As noted earlier, the first pass of what I'm working on is the software emulation, but the long-term goal is to fully emulate the 642 computer using register manipulations rather than just emulating the instructions.

At least for now, the target hardware for compiling the system will probably be a minimum 32-bit hardware (like the current intel 32/64 bit chipsets).

One of the USQ20 system is also an 18-bit computer (CP789) - but I don't plan on emulating that for a while yet (if at all - since the 789 was used to manage the KCMX, which was the interface to the older analog fire control systems and not really needed for what I'm initially targeting the project for).