> On May 13, 2019, at 11:31 AM, Ethan Dicks <ethan.di...@gmail.com> wrote:
>
> On Mon, May 13, 2019 at 8:20 AM Paul Koning via cctalk
> <cctalk@classiccmp.org> wrote:
> ...
>> On the subject of custom chips: DEC used gate arrays a lot. For example
>> there is the Pro 380 in which much of the discrete chip logic from the Pro
>> 350 has been absorbed into one or two gate arrays, with all the unnecessary
>> flexibility of the original chips omitted.
>
> What sort of flexibility was omitted? I have both models and the
> board layout difference is obvious (there's so much room on the Pro380
> that it has a huge RAM field right on the mainboard instead of on two
> daughter cards (plus any on the CTI bus).
The 350 uses Intel chips for various functions, for example an interrupt
controller chip (from the original PC, I think?) that has a bunch of mode
choices. Some of them are typical Intel bad ideas, like edge triggered
interrupts. Also, vectors are programmable.
In the DEC software one choice was used and the others were not needed; for
example, interrupts are level triggered because that's the only right way to do
it. So in the 380, the gate array implements an interrupt controller that's
like the used settings of the 350 chips, but omitting all the other modes that
aren't used.
As a result, emulating a 380 is quite a lot easier than emulating a 350, unless
you make it a "380 style subset of the 350".
paul
