On 16 Oct 2000, Chris G. Demetriou wrote:

> >  - At the moment, the upc driver reads the chip's configuration registers,
> >    and uses the results to locate the child devices.  Is this sensibly
> >    possible with an isa attachment?  If not, we have to fall back to
> >    probing for each device, which is grotty.
> 
> hence my comment about doing a direct-config variant of ISA, which is
> what you want if you don't want each device to probe.

What do you mean by "a direct-config variant of ISA" that makes it
different from what upc (or amiga supio) currently uses (if anything)?

> >  - Devices attached at isa are expected to call bus_space_map themselves,
> >    which means the relevant bus_space_tag_t has to contain enough
> >    information to locate the UPC in the system's I/O space.  This is
> >    probably only a problem if you use a very simple bus_space
> >    implementation, though.
> 
> I don't think i understand the issue you're facing.  do you have a
> non-flat I/O space, or what?

Well, at the moment, the arm26 calculates the I/O address as:
  handle + (offset << tag)

This means that a tag doesn't hold enough information to identify
somewhere in the address space.  This is arguably a bug in the arm26
bus_space though.

> if it's effectively flat, you could go the route where the I/O
> addresses are large numbers, rather than small numbers.  8-)

Could do.  I only use two or three bits of the tag at the moment, after
all.

-- 
Ben Harris                                                   <bjh21@netbsd.org>
Portmaster, NetBSD/arm26               <URL:http://www.netbsd.org/Ports/arm26/>