[Coco] CoCo 4/5 perspectives: close hardware emulation?

[Mark McDougall]

Joel Ewy wrote:

> The conventional wisdom is that it's infeasible for hobbyists to develop
> their own PCI cards.  But how difficult would it really be in comparison
> to things we're already suggesting.  I'm not suggesting hand-building
> our own PC boards, but just designing the simplest possible PCI card
> with nothing but the bus interface logic and a big flash ROM.  

A PCI card would be beyond most - not all - hobbyists - at least in terms of 
layout. Even at 33MHz, there are requirements in terms of maximum PCB trace 
lengths for the PCI signals.

Bus interface logic *requires* a PCI bridge chip - something from PLX for 
example.

Not quite sure what you're going to gain from loading from ROM on a PCI card 
- writing a custom boot loader to boot from HDD/CF would be a *much* cheaper 
and easier option and IMHO imperceptibly slower. With a custom boot loader 
and no OS, you're talking about loading a few MB worth of software at around 
100MB/s.

Besides, the PCI spec does not allow execution-in-place for expansion ROMs - 
the system needs to copy ROM contents into shadow RAM - and that's going to 
take time as well.

Regards,

-- 
|              Mark McDougall                | "Electrical Engineers do it
|  <http://members.iinet.net.au/~msmcdoug>   |   with less resistance!"