>>>>> "David" == David  <David@ixibbs.iximd.com> writes:

  David> If ISA isn't native to SH4, what kind of buses are?  If the BBA "in a
  David> sence" is a PCI device then is PCI native to SH4.

I'm not sure what you mean by "native to SH4", but there is a "shb"
driver that handles the CPU bus.  Connected to this driver there is
for example a "g2bus" driver that handles the G2 bus.  Connected to
this is a "gapspci" driver, that handles the PCI bus created by the
SEGA glue chip in the BBA.  So the logical structure for the BBA looks
something like this (each "box" is physical chip):

 '-------`         '--------`         '--------`           '------`
 |       | CPU bus | System | G2 bus  |  GAPS  |  PCI bus  | RTK  |
 |  SH4  |=========|  ASIC  |=========|  PCI   |===========| 8139 |
 |       |  "shb"  |        | "g2bus" | bridge | "gapspci" | chip |
 `-------'         `--------'         `--------'           `------'
\-------------------------------/   \------------------------------/
       Inside Dreamcast                       Inside BBA

The "shb" driver is SH3/SH4 specfic, with some dreamcast enhancements
to handle the interrupt controller in the System ASIC.
The "g2bus" and "gapspic" drivers are dreamcast specific.  The driver
for the RTK8139 PCI is machine independent.


  // Marcus