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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada,sci.electronics.basics
Subject: Re: Z80 trst circuit
Date: Fri, 29 Jan 2016 15:55:34 -0600
Organization: JSA Research & Innovation
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Xref: news.eternal-september.org comp.lang.ada:29285
 sci.electronics.basics:22633
Date: 2016-01-29T15:55:34-06:00
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"Luke A. Guest" <laguest@archeia.com> wrote in message 
news:2084722069.475747788.515903.laguest-archeia.com@nntp.aioe.org...
> Randy Brukardt <randy@rrsoftware.com> wrote:
>
>>> Do you have Any advice re this?
>>
>> Not really. Ada 2012 is way different than the subset of Ada 83 that we 
>> had
>> on the Z80. I don't remember off-hand precisely what Ada features were
>> available on that compiler; I know we had some software floating point, 
>> and
>> certainly not any tasking. But certainly there wasn't anything like 
>> tagged
>> types, or dispatching, or preconditions.
>
> You can definitely do multitasking on Z80, I've seen projects that do it,
> they use memory banking to implement it though.

It's surely possible; we did it on the 8086 using early MS-DOS, and that's 
essentially the same sort of hardware (with a 16-times bigger address 
space). And it's the address space that's the problem; our task runtime 
takes up approximately 32K on the 8086, but of course on a pure 16-bit 
processor that would leave almost no space for the program. (The rest of the 
runtime was around 4K, if I remember right.) I'm sure you could do better 
with a Ravenscar task supervisor (that of course didn't exist in 1984), but 
it still would be a substantial amount of the code space available.

We used the equivalent of memory banking to expand the data space on 8086 
processors (it allows our 16-bit compilers to compile programs about 3 times 
larger than they otherwise could), but using that with code would be very 
difficult. <Shivers>

                        Randy.