Date   : Thu, 11 Mar 2010 01:35:48 +0000
From   : theo@... (Theo Markettos)
Subject: Tube on the Archimedes

In article <4B981A03.2050302@...> you wrote:
> To make an assumption of my own, I would imagine the hardware part of 
> the system is fairly simple (in terms of an actual PC); a CPU and the 
> interface-glue chip. This support logic probably recognises certain 
> standard memory locations, so that when the parallel port hardware would 
> be accessed on a normal PC, it would generate some sort of interrupt to 
> bring in the emulation side of things to "read" the operation wanted, do 
> it, then push in the expected response.

Yes, that's pretty much how it works.  The gory details are explained in the
Aleph One PC card DDK if anyone wants to know.  Most of ISA address space is
emulated, though there are also some magic BIOS calls (used for quicker
access to things like the display).

> There are numerous similarities with how the TUBE operates (async slave 
> processor with I/O links to host), but it's an altogether different setup.

Tube is rather simpler, after all.

[snip]
>      Acorn has a history of dicking around when it comes to the serial
>      port - look at the A3xx series (messed up implementation blighted
>      us with special leads forevermore)

That was a bug in the particular type of 6551 they happened to fit to some
machines - the other brands they used later didn't have that problem.  I
don't think a hardware bug in the chip can be counted as Acorn's fault.

>      and the A3000 (no 6551, lame),
>      not to mention the RiscPC (combi-I/O chip can support *TWO* ports
>      but only one is actually present. Pah. Perhaps it looked too hard
>      to bodge the SerialDriver to support more than one port in a nice
>      manner? Pah again. And Pah-more for not supporting USB within the
>      machine. The fact the RiscPC came out in 1994 and USB was devised
>      in 1996 is like totally irrelevant. :-)

I was designing a combo-I/O podule in 1996/7 and wondered about adding USB. 
I think, given how complex it turned out to be, deciding not to was the
right decision.  And there weren't any devices you could buy then anyway :-)

Theo