[rescue] [OT] S: IBM /370 or /390 card

[Andrew Back]

On 12/09/2023 22:45, Joshua Boyd via rescue wrote:
> On 9/12/23 16:37, Dave McGuire via rescue wrote:
>> On 9/12/23 16:25, Mouse via rescue wrote:
>>>>> Wasn't the XT/370 primarily made with 68000s with custom microcode?
>>>>> [...] I'd love to see someone work out how to redo that on a newly
>>>>> made board.
>>>> Since the 68K's control store is in mask ROM on the chip, I think
>>>> that would be a challenge.
>>>
>>> I can't imagine that there would be any difficulty beyond possible lack
>>> of documentation in reimplementing a 68k with writable microcode in a
>>> modern FPGA.
>>
>>    How I interpreted Josh's question was the modification of a 68K's
>> microcode.
> 
> 
> I was originally thinking modify the microcode in the chip, but making a
> cycle accurate microcode compatible 68K in an FPGA to run altered
> microcode would also be cool.  Extra cool if the FPGA's image was
> derived from a scan of the 68k silicon.

Yeah, so we can debate the ethics of preventing others from implementing 
a particular ISA, but imaging an actual silicon die for the purposes of 
copying that design verbatim is surely going to fall foul of the 
protection of mask works IP. Maybe in the US it doesn't apply to designs 
prior to The Semiconductor Chip Protection Act of 1984 — I have no idea 
— but it's not something I'd want to casually suggest doing.

Andrew